Snowfall forecast update

Now that the mesoscale features are becoming more clear and based on latest trends here is updated snowfall map:

Quick hitting storm system to bring snow to southern New England 12/29-12/30/12

An area of low pressure is currently working up the east coast and will be undergoing fairly rapid cyclogenesis over the next 12-18 hours.  This storm will have a solid amount of moisture associated with it, however, the storm will be a fast mover and the strongest lift will only be over the region for a brief amount of time.  Because of these two factors this will help to prevent this storm from dropping much more significant snowfall totals across the region.  If this storm were to move slower we could be looking at widespread amounts of 8''+ across much of the region.  

The storm will be tracking just to the south of southern New England and sliding northeastward towards the southeastern Canadian coastline.  This track will ensure cold air stays locked in place for pretty much the entire region meaning precipitation will be all snow.  It's possible, however, that locations along the CT/RI coastline and along the Cape begin as either a mix of rain/snow or a mix with sleet.  With this potential for mixing across these locations snowfall totals may be held back a bit.

Snowfall will begin breaking out anytime after noon-1 PM as snow flurries/showers ahead of the system move through the region.  While this will be a quick hitting system the height of the storm conditions will be very messy.  Snowfall rates of 1-2'' per hour are likely, perhaps even isolated 3''/HR rates where the strongest banding sets up.  The timeframe for the heaviest snowfall should be between 6 PM-12 AM.  This is when most of the accumulations will occur.  While snowfall will continue through the rest of the evening and overnight hours snowfall rates should be much more modest, below 1''/HR rates.  Snowfall will begin exiting the region from SW to NE beginning around 1-2 AM.

Winds may become a bit gusty as well across portions of the region, especially the southeast coast where winds could gust upwards of 25-35 mph.  While not significant this could lead to some isolated pockets of tree damage or perhaps power outages but this is not expected to be a significant issue.

Below is the forecasted snowfall map.  The area of 5-9'' is where the strongest lift/banding is expected to setup.  It's possible we could see some isolated amounts of 10'' somewhere within this area.  

Significant Storm to Impact New England 12/26/12-12/27/12

Currently there is an area of low pressure located across the Gulf coast states right around LA.  This area of low pressure has been slowly strengthening throughout the afternoon.  This system is already rather potent as it has been responsible for producing severe weather and tornadoes from eastern TX through LA/MS/AL and will continue to produce severe weather across these areas overnight as well as FL and then CS/NC/VA tomorrow as the system continues to deepen.

As the area of low pressure begins to track more northeastward following the spine of the Appalachian Mountains and the main piece of energy associated with the system strengthens we will begin to see a trough developing within the mid and upper level jet streams as depicted by the image below:

 When looking at the orientation of the developing trough we notice that the trough isn't developing in a north-south fashion but a more northwesterly to southeasterly fashion and looking at the image on the right we see a sharply negatively-tilted trough.  The combination of these two features means that there will be very little room for a storm track off-shore.  The rising heights will also allow for the winds in the middle and lower levels of the atmosphere out ahead of the system to shift more southerly and southeasterly.  With the system expected to undergo rapid cyclogenesis (strengthening) allowing for a rapid increase in the mid and low level wind fields this will allow for warmer air to quickly advect into portions of southern New England meaning many locations will see a quick transition from snow to sleet/freezing rain and then eventually rain.  Area to the north and west of the low pressure's center should pretty much remain all snow or see some mixing of sleet/freezing rain.  With this said the heaviest snowfall totals will be located across central/northern New England.

In addition to the mess of precipitation we will be dealing with this system is also expected to produce a period of strong/damaging winds, especially across the coastal areas of CT/RI/SE MA where a warmer low-level airmass will allow for better mixing of the lower atmosphere and where the wind fields will be much stronger.  There will be some very intense lift associated with this system as well so some rumbles of thunder certainly can't be ruled out either.

As usual with out winter storms this forecast will be very, very tricky as many of the thermal profiles, especially during the onset of the storm are very close to either being all snow or a mix of snow/sleet.  High temperatures tomorrow across the region are only expected to get into the mid-30's with dewpoints slowly creeping through the mid-20's.  As the onset of the precip shield starts progressing into the region evaporative cooling will 1) work to increase the moisture content of the atmosphere and 2) Allow for the surface temperatures to drop.  So essentially how warm the temperatures get tomorrow will play a big role in the precip type at the onset across many locations.  We then take a look at the thermal structure of the lower atmosphere.  Out ahead of the system we really don't have a great deal of cold air in place across our region or to our north.  Temperatures from about 925-700mb are only around -3C to -5C and there isn't any strong high pressure system to our north to allow for colder air to stay in place or drain down into our region.  This means that as the system continues to work towards the coast eventually warm air will overspread areas to the south and east of the storm's center allowing for a transition from snow-sleet-freezing rain-rain.  With this let's break down each aspect of the storm into further details and for each state:

Snowfall:

CT:

Precipitation is expected to first start working into CT between 1-3 PM with activity first occurring across the southwest corner of the state and spreading north and east through the remainder of the afternoon.  As of now, thermal profiles are rather tricky as several forecast soundings are very close to being either all snow or a mix of snow/sleet, especially across southern CT.  While surface temperatures are expected to range in the mid-30's or so temperatures aloft from 925-700mb are expected to range from -3C to -5C or so.  This really isn't all that impressive and should make for any snow that is falling to be rather wet.  This also poises difficulties with the forecast as if the precip is on the light side we could be looking more at more of a mixture.  Going with this I would expect everyone to begin as either snow or a mix of snow/sleet (with the mix more likely the closer to the coast you go).  As mentioned above the level of cold air in place isn't all that great and there is no high pressure to our north to reinforce colder air into the region.  We will begin to see warmer air work into the state rather quickly, especially across the coast and this will work to keep snowfall totals across the coast to a minimum and only about a few inches across the interior.  Some locations across the northwest corner of the state where cold air may hang in longer could pick up several inches of snow.  

RI:

Snowfall totals across RI should be kept to a minimum as well and accumulations are expected to remain under 1'' for the entire state.

MA:

As we work into MA this is where snowfall totals will begin to vastly increase, especially across the western and central portions of the state and outside of the CT River Valley in southern Hamden County.  Areas to the east of Worcester county in eastern MA are expected to receive little in the way of snowfall as warmer air will quickly work into these areas.  Areas to the west of Worcester County will have the potential to receive significant snowfall accumulations and snowfall could be on the wet side.  There will also be areas of sleet/freezing rain but we'll look at this hazard a bit further down.

NH/VT/ME

These states will be getting hit the hardest by snowfall accumulations as they will be to the north and west of the storm's center.  Snowfall accumulations here will be rather significant, however, b/c the aitrmass will be a touch colder snow should be more on the dry side.

Freezing rain/icing potential:

CT:

Some locations across interior CT could face a brief period of freezing rain between the transition of snow to rain.  As of now this hazard doesn't look to be a major issue, however, there could be a glaze of accumulation to perhaps just under a tenth of an inch of ice accretion.  With perhaps a few inches of wet snow accumulating, this could add a little extra weight to the snow allowing for the possibility of downed limbs or power lines.

MA:

There could be a corridor across central/southern MA where there is a several hour period of freezing rain, however, at this point it's tough to say if this will actually occur.  If this does occur the potential would exist for a few tenths of an inch of ice accretion.  With the potential for higher snowfall accumulations across these areas the risk for downed limbs/power lines would certainly be increased.  This will have to be watched as we get closer.

Rainfall:

For areas across southern CT/RI/eastern MA rainfall will be the main precipitation concern.  Rainfall totals of 1-2'' can be expected and this could lead to pockets of flash flooding/poor drainage flooding.

Strong/Damaging Winds:

With a very strong low-level jet working into the region we will be looking at a period of very strong winds, especially across southern CT/RI/SE MA where the core of the low-level jet will be located and where a warmer low-level airmass will lead to a little more in the way of mixing.  Across these areas winds will be sustained between 25-35 mph with wind gusts as high as 55 mph.  With heavy rains and a somewhat saturated ground this could lead to pockets of tree damage/power outages.  Elsewhere across the region winds should be sustained from 15-25 mph with wind gusts as high as 35-45 mph possible, especially across the higher elevations.

The height of the storm will be occurring during the overnight hours of Wednesday into Thursday lasting through mid-AM before the storm finally begins to taper down.  Below are graphics of what to expect:

Quick snowfall update

After looking at things this AM I probably should have stuck with my original snowfall call.  Given that, here is the original snowfall map with some slight additions, mainly to add an area where some locally higher amounts may occur to due heavier banding. 

Updated snowfall forecast for 11/27/12...looks like more snow

Yet another touch and complex snowfall forecast for our region as latest computer model guidance has trended stronger with the developing wave of low pressure tomorrow which will be sliding just to the south of our region.  With computer forecast models now deepening and strengthening the system quicker and closer to the coast, this will allow for more in the way of moisture and stronger lift to at least work into a portion of the region.  Given this it does appear some of the snowfall totals from the previous forecast will have to be bumped up a bit.

The highest uncertainty with this forecast will be out across eastern MA.  Computer forecast models have have the combination of strongest lift and highest moisture over this area, however, signals of an inverted trough setting up across SE MA could actually allow for warmer marine air to contaminate the lowest 2000' of the atmosphere giving this area more in the way of rain or a mix of rain/snow, cutting down snowfall totals.  On the western side of this boundary is where the highest snowfall totals are going to occur as on the western side these locations will still be under the strongest lift/highest moisture and will also be cold enough to support all or mainly all snow.  The million dollar question (and is always the million dollar question) is where this boundary, known as the "coastal front" sets up.

Snowfall should begin breaking out in the early to mid morning hours and start off light in intensity.  In fact, for much of the storm's duration the intensity will only range from light to moderate, with the exception being some areas from SE CT into RI and interior SE MA where stronger lift aloft will allow for more periods of higher intensity snows (possibly in the range of 1'' to 1.5'' per hour).  Snow will be ongoing throughout much of the afternoon and overnight periods when the system will finally begin to wind down as it moves off to the north and east.  Some leftover flurries are still possible on Wednesday, especially across eastern southern New England.

Areas along the RI/SE MA coast will also experience a mix of rain/snow, especially during the afternoon hours when temperatures in the lowest 1000-1500' of the atmosphere are a touch on the warm side and especially when the precip rates are very light.  During bursts of heavier precipitation, any precip would be mainly snow.

Given the above this is what I would expect:

:

 

Tuesday, November 27th, 2012 light snowfall event

A weak wave or perhaps multiple weak waves of energy will ride along a boundary just to our south throughout the day on Tuesday extending into early Wednesday.  While some computer models eventually develop these waves into a somewhat unorganized but juicy storm, the weather pattern for this "cyclogenesis" (development/deepening of a low pressure system) to occur close to the coast is not favorable, therefore, these waves will remain weak.

Several computer models are showing some decent moisture being associated with these waves (at least decent enough to lead to the production of snow) as well as lift just strong enough to lead to the development of precipitation, and given the thermal temperature profiles of the atmosphere we should be looking at mainly snow, though areas along the coast may have to deal with some mixing.

While one of the more reliable computer models shows very little, if any precipitation making it into the region, several other computer models are in agreement that we will see a period of light snow spreading into the region.  However, given the one more reliable computer model keeping everything offshore leads me to feel that I wouldn't not be surprised if many of us nothing more than flurries.

Given this, the best shot at "accumulating" snow will be well to the south and east of the MA Pike and any accumulations should generally remain around an inch or so with a few locations perhaps picking up 2-3'', especially if we see some heavier bands work in.  Since this system will be occurring more in the daytime with the sun angle not quite at it's lowest yet, surface temperatures may warm up into the mid-30's.  This should really help to prevent much in the way of accumulations of non-grassy surfaces, especially considering the snowfall intensity will not be all that heavy.  If we were dealing with higher intensity snowfalls these mid-30's surface temps would not be an issue.

Snowfall should begin during the morning hours of Tuesday and virtually go on and off throughout the entire day and lasting into the overnight hours with perhaps a few flurries leftover very early Wednesday AM.

Below is the forecast map:

 

Snowfall Total Update

What a winter storm...wow!  The mesoscale features and processes involved with them storm have been incredible and when dealing with winter storms and snowfall forecasts it is these features which can absolutely kill snowfall forecasts b/c our computer models just aren't fine enough to pick up on these features in their entirety.  Anyways, we have seen some VERY impressive banding set up from central NJ up through the NYC area and into SW CT along with another band (although a bit less impressive) across SE CT into RI.  The banding from NJ to SW CT just does not want to move and models continue to indicate this band will sit over these areas for at least several more hours before rotating through the rest of the state.  once it begins to rotate through the rest of the state the band will begin to run into some much drier air advecting in from the north resulting in weakening of the band and keeping the more impressive snowfall totals across the SW part of the state.   It should also be noted isolated power outages are possible as well as winds continue to gust.  Here is updated snowfall map.

Nor'easter to bring snow/sleet/rain/strong winds/coastal flooding 11/7-11/8

We are a little more than a week removed from the devastating impacts Hurricane Sandy left behind and unfortunately it appears much of the Northeast will be impacted by a strong coastal storm.  Thankfully, this system will be nothing similar to that of Sandy, however, this storm will present issues, especially along the coastal plain from NJ up through SNE where strong/damaging winds will occur along with more coastal flooding and for the areas that were severely impacted from Sandy this is the last thing they need.

This will be a very challenging forecast as this system will not only be presenting us with rain but with snowfall/sleet and perhaps even some freezing rain as well and pining down who exactly sees snow and how much will be real difficult.  There were be alot of impacts from this storm so let's get right to it and break it all down!

Snowfall

Over the past few days computer forecast models have trended colder, and colder with the airmass preceding the storm and for a duration of the storm and with this much of the region with the exception of the coastal plain will receive minor accumulations of snowfall with the highest totals occurring across the Northwest Hills of CT into the Berkshires of MA.  It's also possible many locations within the snow zone will mix with sleet or even completely change over to sleet at some point during the storm and there could be some pockets of freezing rain as well.  The snow will be very wet and heavy meaning it will cling to trees/power lines.  While accumulations are expected to be on the lower side, we will still deal with some  pockets of tree damage and power outages, especially when combined with the potential for strong winds...more on this below.

Rainfall

While much of the coastal Plain will be mostly rain some mixing or brief periods of snow is possible across some of these locations.  Rainfall amounts should generally be in the 0.50'' to 1.50'' range and with this the threat for flash flooding will be on the lower side, however, the normal typical flood prone areas could see pockets of flooding.

Damaging Winds

Winds will be the biggest issue right along the coastal plain from NJ up through southern CT/southern RI and right into far SE MA.  Across these areas winds will be sustained anywhere from 25-35 mph with wind gusts as high as 60 mph.  Across far inland areas winds aren't expected to be this strong but they may gust as high as 30-40 mph.  With the forecast for strong winds this will lead to pockets of tree damage/power outages, especially across the coastal Plain..more on this below.

Power Outages:

Across inland locations where minor accumulations of wet snow are expected along with gusty winds there will be pockets of tree damages and power outage but nowhere near to the degree that we experienced with Sandy.  Across the coastal Plain where winds are expected to be much stronger power outages will be more on the scattered side than isolated side and this is certainly not good news at all for the restoration process in areas still experiencing outages and issues from Sandy.

Coastal Flooding

Coastal flooding is once again expected from NJ up through coastal CT/RI/SE MA as higher than normal tides will coincide with the height of the storm leading to high storm surge...storm surge in spots can be anywhere from 4-6' which is terrible for the areas that were heavily damaged/destroyed by Sandy.

Precip will begin across NJ/NYC area overnight tonight and slowly spread northward into southern New England by early to mid afternoon.  The heaviest of the precip is expected to occur within a window of about  6-8 hours then the system is expected to weaken which will decrease precipitation rates.  While the storm will be a slow mover and stall this will allow precip to occur on and off into much of Thursday.  Below is a map with snowfall amounts as well as other impacts expected with the storm:

Updates to Hurricane Sandy

During the overnight hours Hurricane Sandy actually strengthened.  For the better part of the past few days Hurricane Sandy remained steady with maximum sustained winds of about 75 mph with gusts in the 85-90 mph range.  As Hurricane Sandy continued to move in a NE direction she went over the warm waters of the Gulf Stream and with this she strengthened.  Hurricane Aircraft hunters have found that maximum sustained winds have increased to 85 mph with wind gusts as high as 105-110 mph and a central pressure of 946mb which ties the record for lowest pressure recorded north of Cape Hatteras, NC and when all said and done Sandy will be the Queen in this regards.  With this let's get right into the specifics...

Coastal Flooding/Beach Erosion  

It's now becoming more likely that the coastline of central/northern NJ northward into the lowest suburbs of NYC to the south facing shore of Long Island to western coastal CT will experience catastrophic storm surge of record levels and extremely damaging coastal flooding.  This will be a life threatening situation to anyone who was told to evacuate who chose not to.  Any buildings right along the water are likely to experience extreme damage or complete destruction.  Elsewhere across coastal CT/RI/E MA/NH/ME significant coastal flooding/storm surge is expected and will also pose a threat to property on the water front.  If you know anyone in an area which was told to evacuate and chose not to get the word to them to evacuate before it's too late and time is basically running out for them to do so safely.

Damaging Winds  

We are looking at widespread damaging winds all the way from NJ up to the US/Canadian Border.  We will be looking at widespread damaging winds lasting as long as 24-36 hours which will lead to widespread tree/power line damage and widespread power outages, potentially lasting for several days in the hardest hit spots.  The strongest wind gusts are expected to occur across the CT coast/RI coast/SE MA where winds could gust as high as 75-85 mph.  Here, during the peak sustained winds could be in the 45-55 mph range.

Rain/Flood Threat

We aren't looking at much in the way of rainfall as the bulk of the rain will be off to our west and southwest.  With that said we could see some spots pick up 1-2'' of rainfall with some isolated amounts of 3-4''.  With this the flooding threat will be real low, however, areas along rivers/streams/brooks may experience some flooding and especially the typical flood prone areas.

Thunderstorm/Tornado Threat

Typically with landfalling tropical system you induce the threat for isolated tornadoes.  While that potential did look extremely low leading up to the event, there have been some changes which have lead to a slight increase in the potential.  Later on this afternoon we will be experiencing some cold air advection in the mid-levels of the atmosphere along with increasing temps/dewpoints in the lower levels of the atmosphere...this will lead to a slight increase in instability and with that we can't rule out the potential for low topped t'storms and given the very strong wind shear there is a low threat for an isolated tornado.  If we are to get t'storms they will have the potential to mix down much stronger winds locally as well.  This potential will have to be CLOSELY watched.

Breaks/Peaks of Sun

There will be a dry slot moving into the region later on...with this dry slot comes the potential for some breaks or peak of sunshine.  If you happen to witness any sunshine today DO NOT let that get your guard down.  Any sunshine will only INCREASE the damaging wind potential and the winds we experience.  The sun would warm the atmosphere enhancing mixing allowing for much stronger winds to mix down.  If this occurs we could locally increase the gusts by as much as 10 to even 20 mph.

Below are graphics of all the mentioned threats:

Coastal Flooding/Storm Surge

Damaging Winds

T'storm/tornado threat

Update on Hurricane Sandy impacts

Latest computer model data continues to indicate the much of NJ/NYC/LI/CT/RI/SE MA will see the most extreme impacts from Hurricane Sandy when taking into account coastal flooding and damaging wind potential.  When looking at rainfall/flash flooding associated with the rainfall that threat will exist more to our southwest/west, however, we will still deal with some isolated flash flooding here.  Given latest guidance here are the hazards at hand:

Coastal Flooding/Beach Erosion

We are looking at major to perhaps catastrophic coastal flooding/beach erosion.  While significant coastal flooding will occur from the Jersey shore following the coastline up through southern ME the potential for catastrophic flooding looks to exist from the lower suburbs of NYC extending into western areas of Long Island South along coastal CT as well as the south shore of Long Island sound.  For these mentioned areas the difference between significant coastal flooding/beach erosion occurring and catastrophic coastal flooding/beach erosion occurring will all depend on exactly when Sandy makes landfall.  The National Hurricane Center is forecasting Sandy to make landfall around 2:00 AM in central NJ, however, some latest models are actually speeding up the timing of Sandy meaning she could make landfall several hours earlier than that.  Forecasted high tides tomorrow night are around midnight, meaning if we see a landfall closer to the high tides that will be the worst case scenario in terms of coastal flooding/beach erosion as we'd be looking about storm surge as high as 10-12'...which would be record and historic levels.  A landfall hours several hours earlier would likely result in storm surge being a few feet less which would probably negate catastrophic type of damage.  Either way you slice it, the coast is in for bad times.  Looking at substantial damage and/or complete destruction to any buildings along the shore along with significant flooding damage.  For anyone who has decided to disobey evacuations in areas ordered to do so this will be a life threatening situation.  

Damaging Winds

Pretty much all of New England is forecasted to experience widespread damaging winds from Sandy as well will be located in the portion of the storm with the strongest winds. As of now it appears the strongest sustained winds will be across southern CT/RI/SE MA where sustained winds during the height of the storm will be as strong as 45-55 mph with wind gusts as high as 65-75 mph.  Even coastal NH/ME could experience similar conditions.  Elsewhere across CT/MA up through MA and into central VT/NH during the height of the storm winds will be sustained between 35-45 mph with wind gusts as high as 55-65 mph.  Across central/northern VT/NH extending into southern ME during the height of the storm wind will be sustained between 25-35 mph with wind gusts as high as 50-60 mph.  It should be noted that if Sandy ends up making landfall further north than forecasted (which is still certainly possible) we could increase these winds by as much as 10-20 mph, especially across CT/RI/SE MA.  Not only will we be dealing with winds of this magnitude but the duration of the damaging winds will be very, very long.  In fact, we could be dealing with damaging winds for as long as 24-36 hours.  In the end this will lead to widespread wind damage with downed trees/power poles/power lines and widespread power outages.  For the areas that get hit hard power outages of at least 3-4 days could be expected.

Rainfall/Flood threat

While the heaviest and most extreme rainfall totals and flooding will occur well to our west/southwest where as much as 5-10'' of rainfall could occur rainfall/flooding is not expected to be a major issues here, in fact, rainfall totals aren't expected to exceed 4'' and totals this high should be more if an isolated occurrence.  Given this flooding will not be a widespread issue, however, can't rule out some isolated flooding, especially areas near rivers/streams/brooks or the typical flood prone areas.

We are already beginning to see impacts from the storm with increased waves/surf and winds have been slowly increasing as well.  As we work through the evening/overnight conditions will deteriorate very rapidly as winds will begin to vastly increase.  We will be impacted through Tuesday, however, by then the winds will have subsided as Sandy will be weakening over land but we can't rule out on and off showers.  This is a very dangerous storm with impacts to life and property and everyone should have taken the appropriate measures.

Below is a graphic:

Historic Storm in Sandy to impact the Northeast

Before we get into the gist of things I would like to begin by saying while we have expectations for Sandy and expecting extreme impacts in the end we just really don't know what will happen.  What is going on right now is in uncharted territory.  Sandy, being a tropical system is defined as a warm-core system, this means that as you move closer to the center of the storm the temperatures increase.  Typically, as tropical systems gain latitude and approach our neck of the woods they begin to transition form being a warm-core system to more of a cold-core system.  This just means that as you draw closer to the center of the system temperatures no longer increase but begin to decrease.  Some tropical computer models have actually been suggesting that Sandy may actually remain a warm-core system much further north than usual and the transition process will be slower than what we typically see.  This alone actually isn't really uncharted, however, when you take into account the developing trough to our west and it's interaction with Sandy this is where we get into the uncharted territory.

We see troughs phase with systems moving up the coast several times throughout the year, however, we have never really seen such a deep trough associated with the Polar Jet phase with a warm-core system...once this phasing takes place Sandy will actually begin moving either due west towards the US coast or moving towards the US Coast in a more northwesterly direction...this is uncharted.  This phasing will rapidly intensify Sandy to become a MONSTER storm and lead to the build up of incredibly high waves, possibly as high as 25-35' crashing into the coast line from southern NJ up through eastern southern New England.

With this said, with what computer models are showing and with what we understand about meteorology and how the atmosphere we would expected to see some extremely damaging impacts from Sandy for much of the region.  Because we really have nothing to compare this too this does make it difficult to really have a true understanding of how this will unfold.  Now that this was said let's get down and dirty.

As mentioned above, Sandy which is a very large in size will eventually be tugged in west towards the coast by a deepening trough associated with the Polar Jet and phase.  Once this phasing occurs Sandy will undergo what is called rapid bombogenesis...this is just a fancy word for saying she will rapidly intensify.  As Sandy continues to grow in size and phase with the trough/Polar Jet the wind fields just above the surface will expand, this will mean winds just above the surface will be very strong and for a quite a distance away from the storm's center.  In fact, computer models are generating wind speeds of anywhere from 60 knots to as much as 100 knots as close as 2000-3000ft above the surface!  This is absolutely remarkable to see winds of that caliber so close to the surface.  With Sandy increasing in size and very strong winds over the ocean wave heights will rapidly build.  As Sandy continues to close in on land very high waves will begin crashing into much of the eastern sea board from the Carolina's to the outer Cape.  This system will also be loaded with moisture so there will be some extremely heavy rainfall as well.

The one question we are still faced with is where Sandy will make landfall.  We are still uncertain as to exactly where Sandy will make landfall.  Some computer guidance suggests she will make landfall around southern NJ/DE area while other computer models suggest she will make landfall further northward...around northern NJ or perhaps even near NYC.  While the first mentioned scenario would still probably bring major impacts to the entire region the second scenario would bring extreme issues to the region.  While the computer models are giving us uncertainties within the track based on the pattern setup along with other factors I would think we see a landfall closer to the northern NJ/NYC solution meaning we would see the worst case scenario across our region.  With this said we will now break down all the hazards and what we should expect from each:

Coastal Flooding:

It's appearing extremely likely we will see at least major coastal flooding from NJ up to Long Island Sound, coastal MA and coastal MA.  In fact, we may be looking at the potential for catastrophic coastal flooding/beach erosion across the areas as wave heights could potentially exceed 25-35'.  When taking into account a full moon and high tides, if the highest wave heights occur during high tide we would be looking at catastrophic coastal flooding across many coastline areas causing substantial damage and destruction to any buildings that are located right along the coast.

Damaging Winds:

Damaging winds can be expected even a far distance from the Sandy's center.  In fact, the threat for damaging winds should extend as far north as portions of VT/NH.  Depending on exact landfall, areas across NJ/SE NY/coastal CT/RI/SE MA could see sustained winds as strong as 40-50 mph with wind gusts exceeding 60-70 mph with gusts as high as 80 mph possible.  A bit further inland we could see sustained winds of 30-40 mph with gusts as high as 50-60 mph and perhaps even as high as 70 mph...this would include all of CT up through central MA.  Further north from here sustained winds of 25-35 mph is possible with gusts as high as 45-50 mph possible.  For the higher elevations of northern New England above 1000' and especially 2000' winds could gusts as high as 65-75 mph.  Not only will we be looking at the potential for such strong sustained winds and extremely strong wind gusts but the duration of these winds could last for up to 24-hours, although the higher end range of the gusts should be closer to 8-12 hours.  Winds of this magnitude for such a long duration would lead to widespread tree damage/power line damage resulting in widespread power outages and leaving some people in the dark for days.

Torrential Rains/Inland Flooding:

The heaviest rainfall totals are expected to be to our southwest and west where as much as 5-8'' of rainfall can be expected, however, across New England some areas will receive as much as 4-6'' of rainfall.  What we have to watch for are areas just to the east of the Berkshire Mountains, Worcester Hill, Green Mountains, and White Mountains as SE/E winds would lead to upsloping, making for areas of very intense rainfall rates leading to higher totals.  While the inland flooding threat doesn't appear to be too extreme we certainly will see areas of flooding, especially along rivers/streams/brooks.

Impacts from Sandy may begin as early as tomorrow evening (however, waves/surf will begin increasing as early as tonight) as winds begin to slightly pick up and bands of heavy showers move into the region.  The worst of Sandy is expected to occur between late overnight Sunday, lasting through all of Monday and into the first part of Tuesday.  This is expected to be a very dangerous storm causing numerous issues across a very large area.  Below is a graphic showing where the main hazards exist:

Hurricane Sandy to bring major impacts to much of the Northeast

As we continue to draw closer to the end of the weekend and beginning of next week confidence continues to rapidly increase that much of the East coast, from the Carolina's up through New England will be experiencing extreme issues.  While technically Sandy may be classified as a strong Tropical Storm or weak Hurricane by the time she gets up this way DO NOT and I stress DO NOT take that as this being any less extreme.  Strong blocking in the northern Atlantic will help prevent Sandy from escaping out to sea and keep her closer to the East Coast.  At the same time the Polar Jet working through the central US will rapidly amplify developing a very deep trough.  Computer models indicate Sandy will phase "combine" with this Polar Jet/Trough and once this occurs Sandy will undergo rapid intensification.

Sandy will create extreme issues up and down the East Coast with extremely damaging coastal flooding/beach erosion, very strong/damaging winds, widespread power outages, and numerous tree/power line damage.

For us here in southern New England there remain two possible scenarios;

1) Over the past few days there has been a set of computer models which have Sandy making landfall around the Delmarva or even as far south as MD.  In this scenario the worst conditions across southern New England would be across the coast where serious coastal flooding would occur along with very strong wind gusts leading to tree/power line damage across the coastal Plain.  Further inland, the effects would be much more minimal, besides heavy rain and isolated flash flooding winds would be a non-issue with the exception of a few strong gusts potentially leading to isolated power outages.

2) There is another camp of computer models which have Sandy making landfall further north, possibly as far north as NYC/western LI area or northeastern NJ.  This would be the worse case scenario for southern New England.  In this scenario we would be looking at extreme coastal flooding/beach erosion posing a threat to building close to the water.  There would be widespread damaging winds; both sustained and gusts, leading to widespread power outages and tree/power line damage.  We'd be looking at a several hour or more period of very intense winds.

Of these two scenarios which should we expect?  Unfortunately computer models seem to be converging on solution number two.  It's becoming quite apparent that a landfall further north will end up being the outcome and this would pose a significant risk to much of southern New England.  While it's still very possible a further south landfall occurs everyone should begin (if not already) preparing for a very damaging storm.  Anyone living close to the coast should evacuate as the risk for coastal flooding could pose a threat to lives.  With the potential for a prolonged period of damaging winds everyone should stock up on extra non-perishable food items, water, batteries, flashlights, and radios.  While the less extreme solution could certainly verify it's much better to be fully prepared now rather than being caught off guard.

By tomorrow evening more specifics will be given, especially with regards to how strong we can expect the winds to be.

What's up with Sandy? Potential for major impacts along the East Coast

If you haven't heard about Hurricane Sandy by now you will very, very shortly.  sandy developed in the southern Caribbean south of Cuba/Jamaica and actually rapidly intensified over the island to a very strong Category 2 Hurricane.  Below is the forecasted track of Sandy by the National Hurricane Center:

The National Hurricane Center is forecasting Sandy to remain a Hurricane to just east of the Carolina's while weakening and eventually weakening to a Tropical Storm just off the Jersey coast.  Now you may think that b/c it's expected to weaken to a Tropical Storm it won't be that bad here...that assumption would be 100% false.  In this case there will be a trough associated with the Polar Jet Stream working eastward through the United States.  Below is a graphic from one of the computer forecast models (the GFS) for 7:00 AM Sunday showing the trough:

You will also notice an area circled in red.  These two highlighted features will prove to be EXTREMELY important with what Sandy does as she travels northward.  First we will take a look into the area highlighted in red:

This area circled in red is showing another area of low pressure.  b/c of the position and location of this low pressure this is referred to as a "blocking" low.  When low pressures are situated in this location they are referred to as blocking lows b/c they virtually can inhibit storm systems from drifting out into the open Atlantic and keep them closer to the US Coast.  In the end it's all going to come down to the strength and even location of the blocking.  If the blocking is on the stronger side that will vastly increase the chances that Sandy will have to track closer to the East coast.  If this block is on the weaker side this would give Sandy the chance to actually work out more towards the Atlantic.  At this time, however, it appears that this block will remain strong enough to prevent Sandy from escaping to the east and into the open Atlantic.

As far as the trough goes, this trough is important b/c eventually the trough is expected to phase with or "combine" with Sandy, it's just a matter of where this occurs.  Computer models are starting to come together in agreeing that this phasing will occur much earlier rather than later...possibly somewhere just off the Carolina coastline.  Once Sandy phases with this trough along with the Polar Jet Sandy will under go rapid and severe intensification.  

What to take off this as of now?

It's still a bit too early to panic and worry, however, if computer models at this time tomorrow continue to hint at this potential hard it will be time to start preparing for major impacts form this system.  These impacts would include:

• Severe coastal flooding/beach erosion.  Coastal flooding could be extremely serious, and could be a major hazard to any structures located close to the waters.  
• Damaging Winds.  A rapidly deepening system along with an area of high pressure to our north and blocking low to our northeast would create a very strong pressure gradient over the region enhancing the potential for very strong/damaging winds.  Potential for widespread tree damage/power outages would be likely, especially with many trees still having leaves on them and the ground being very saturated leading to weakened tree roots.
• Torrential Rains/inland flooding.  The potential would exist for over several inches of rainfall across the entire region leading to rapidly rising streams/rivers/brooks.  Heavy rainfall rates over a prolonged period of time would eventually lead to areas of inland flooding, especially along rivers/streams/brooks.  

Again, at this point it's still a bit too early to really get into the specifics but the potential and confidence is increasing that there will be serious impacts along the East coast but it's unclear as to what areas will receive the most severe impacts.  All of these details will continued to be narrowed down and answered over the coming days.

If you're looking to prepare the best thing you can do is just stock up on some extra food (especially canned foods and such in case you lose power), bottled water, batteries, flashlights, candles, blankets, and radios.  

impacts could begin as early as Sunday evening, however, it appears it would be more overnight Sunday through early Tuesday but these details will also be ironed out as we get closer.  

End of October storm?

We are now entering the third week of October and the transition from summer to autumn is already well underway as the leaves have gone through the color changing process and trees are beginning to lose their leaves.  While the weather during this third week of the month will be quite tranquil with temperatures running above-average for the most part unsettled weather looms on the doorstep.

In the southern Caribbean, Tropical Storm Sandy has developed south of Jamaica is is expected to slowly track northward over the next several days.  

(National Hurricane Center graphic of Tropical Storm Sandy and it's expected movement through Saturday)

Medium/long range computer models all indicate that Sandy will continue slowly tracking to the north through the remainder of the week and next weekend into the western Atlantic just east of the United States.  While some computer guidance does suggest slight strengthening of Sandy over the course of this period it doesn't appear all that likely she will reach hurricane strength as atmospheric conditions don't appear to be very favorable.  Eventually she will be working into an area of enhanced wind shear and some drier air streaming off the United States and both will eventually inhibit her from going through rapid/intense strengthening.  

While Sandy is slowly making her journey northward some interesting developments will be ongoing across the United States, the central/northern Atlantic Ocean, as well as in and around the Aleutians near Alaska and how these developments unfold across the aforementioned areas will impact what happens with Sandy and where she heads once she gets into the Atlantic.  First, we will take a look at the United States and how the computer models evolve the developing upper air pattern over the United States.

As we move towards the weekend computer models show a developing trough associated with the Polar Jet Stream working into the northwestern portion of the United States sliding an Arctic cold front eastward.  There is agreement within the computer models that as this trough works through the country the trough will begin to amplify and strengthen causing it to dig further south.  In response to the digging trough across the central United States a ridge would be developing across the eastern United States extending northward into eastern Canada.  How this trough develops and how strong (or how far south it digs) will play a major role in what happens with Sandy as it moves into the western Atlantic.  We'll get more into why a bit further down.

Now onto the central/northern Atlantic and the potential developments there.  Computer models are showing the continued weakening area of high pressure located over the Azores as the area of low pressure that is situated between Greenland and Iceland.  When this occurs this leads to what is known as a "blocking pattern".  This is termed blocking b/c the weaker area of low pressure located between Greenland/Iceland leads to ridging in the northern Atlantic, this can prevent storm systems from escaping out to sea and keep them closer to the east coast.  The strength of this northern Atlantic ridging will also play a major role in what happens with Sandy.  

When looking across the northern Pacific Ocean up around the Gulf of Alaska computer models are also struggling with the handling and placement of the Aleutian Ridge.  This will have major impacts upstream as the strength/placement of the Aleutian ridge will vastly impact the strength of the troughing across the central United States which would affect the strength of the riding across the eastern United States and western Atlantic. Now to tie these three paragraphs together!

Below is an ensemble mean showing the 500mb height anomalies across North America Saturday evening.  The image is displaying a fairly deep trough across the central United States with a massive ridge along the east coast and western Atlantic:

  

Below is an ensemble mean showing the 500mb height anomalies across the entire northern Hemisphere Saturday evening...for this graphic we will just focus on the highlighted area showing the ridging in and around the Aleutian Islands near Alaska: 

Below is an ensemble mean showing the 500mb height anomalies across the entire northern Hemisphere Saturday evening...for this graphic we will pay attention to the highlighted area across the northern Atlantic near eastern Canada and south of Greenland:

In the end the strength/placement of the Aleutian ridge will play a major role in how the upper air pattern across the United States develops.  The stronger the Aleutian ridge and the more the center of the ridge is placed over the Aleutians the stronger the ridging just west of the western United States will be and the deeper the trough across the central United States will become which will result in a much stronger ridge across the east coast and western Atlantic.  The weaker the Aleutian ridge and if it becomes further displaced from being centered over the Aleutian Islands this would flatted the ridging west of the United States and prevent the trough along the central United States from deepening too far south leading to a more flat ridge along the east coast of the United States and western Atlantic which would affect the strength of the blocking in the northern Atlantic.  The strength of the northern Atlantic blocking will be highly crucial as well as the stronger the blocking the less chance there is of Sandy escaping and moving into the Atlantic and a much higher chance of Sandy staying closer to the east coast and working northward.  

Over the past few days several medium and long-range forecast models have been showing that the riding in and around the Aleutians may be strong enough allowing for deeper troughing in the central United States and stronger ridging across the eastern United States and western Atlantic creating stronger blocking allowing for Sandy to work very close to the east coast.  By early next week, some of the models have Sandy actually interacting and phasing "combining" with the trough and the associated Polar Jet.  in this scenario we would see a rapidly intensifying storm system.  

What should we make of all this...

The first thing to keep in mind here is this is all 7+ days out there and the accuracy of computer models in that range is very, very low.  In this range, often times computer models will tend to dig those troughs too deep as they get to crazy with the strength of factors like blocking and ridging (or troughing) around the Aleutians.  Computer models also LOVE to go phase happy with systems in the Atlantic and troughs along the East coast.  So until we get closer (inside of 4-days) we shouldn't take much out of these extreme solutions.

With this said the pattern does appear that it will become at least favorable for a period of unsettled weather, somewhere in the Monday-Wednesday timeframe with at the least potential for some periods of rain across the Northeast.  As we move further through the week and closer to next week details will become much more clear as to how the pattern will evolve and what potential impacts we may see.  

 

Anniversary of the October 3rd, 1979 Windsor Locks Tornado.

CT is no stranger to tornadoes, in fact since official records have been kept since 1950 CT has had 91 confirmed tornadoes (as of 2011) for an average of 1.49 per year.  Typically our tornadoes are on the weaker side and usually don't produce much damage outside of downed trees/power poles.  Very rarely do they produce much in the way of significant structural damage, except of course when a tree happens to fall on a building.  Of the 91 confirmed tornadoes only 4 of them have been rated as an F3 and 2 have been rated as an F4.  (Note: Since the implication of the Enhanced-Fujita scale (EF) in February of 2007 CT has not had a tornado rated higher than an EF2).  Most of the tornadoes that occur in CT occur during the months of June-July-August, this is when the combination of heat/humidity can lead to large amounts of instability which is a main ingredient in the development of tornadoes.  Typically when one thinks of October in CT you don't think about thunderstorms, severe weather or tornadoes, you think fall; changing leaves, cooler temperatures and a transition from summer to winter.  However, on Wednesday, October 3rd, 1979 arguably the strongest and most damaging tornado in modern history occurred across portions of Windsor, Windsor Locks, and Suffield, CT.  Not only was the timing incredibly rare for this area but to get such a damaging event from the storm system was even more impressive.

Leading up to October 3rd, 1979 a trough was developing and deepening across southern Canada and the northern Plains of the United States.  With each progressing day the trough continued to sharpen and deepen  dragging a cold front through the heart of the country.  Out ahead of this trough, however, there was another developing system.  On Monday the 1st a diffuse occluded front was draped from northern TX all the way northeastward through the Ohio Valley and just west of PA/NY into Canada.  By Tuesday this boundary had shifted eastward and an area of surface low pressure began developing across the Ohio Valley and slide eastward across the boundary into the Northeast prompting a warm front to shit northward towards southern New England.  Early Wednesday morning (as the graphic shows below) the low pressure had continued to deepen as it northeastward.  At 7:00 AM EST the warm front was located just south of Long Island.  As the morning and early afternoon hours went on and the surface low continued to deepen and move northeast the warm front would eventually end up over northern CT.  This would pump in warmer and more humid air into CT.

During the morning hours a secondary area of low pressure which had developed across North Carolina began working it's way northward and was soon riding up along where the warm front and cold front intersected.  By mid afternoon this feature had finally reached CT and the warm front was lifting through the state.  As the warm front moved through temperatures jumped well into the 70's with the dewpoints not too far behind.  The graphic below shows the 500mb level at 4 PM (an hour after the tornado touchdown); the secondary low was situated just west of CT with the warm front draped across northern CT with the cold front also just to the west of CT.  This placed the entire state in the "triple point" or where the warm front  cold front meet to create an occluded front.  Air associated with the triple point rises very quickly and vigorously and wind shear is quite strong as well.  Associated with this system was a vigorous piece of energy located at 500mb which was associated with very strong mid level wind fields.

With the warm front located across northern CT winds at the surface and just above the ground had switched over to a more southeasterly wind direction (helping to usher in warmer temps and higher dewpoints) while winds from 2000ft on up where more southwesterly with speeds increasing with height.  This yielded to large amounts of 0-1km helicity which meant there was a good deal of atmospheric spin.

According to some reports there were a few breaks of sunshine which occurred across portions of northern CT early on in the afternoon.  This short duration of sun helped to locally spike temperatures upward a bit.  With the combination of a very warm and moist low-level airmass in place along with cold temps in the mid-levels of the atmosphere this lead to some steep mid-level lapse rates which helped to boost up instability values.

During the mid to late morning hours a thunderstorm (which then developed into a supercell) which had developed just south of Long Island Sound was moving due northward and by early afternoon it had made it's way northward into CT.  As the supercell taped into the enhanced shear and pocket of higher instability it quickly strengthened.  Finally around 3:00 PM EST a very large and rain wrapped tornado touched down in the the Poquonock section of Windsor, CT.  Several buildings, including the elementary school were heavily damaged.  The tornado then continued to move through Windsor into Windsor Locks where it heavily damaged the Bradley Air Museum as well as causing major destruction to dozens aircraft and then into Suffield and then finally into the Feeding Hills section of Agawam, MA.  Between Windsor, Windsor Locks, and Suffield dozens of buildings were severely destroyed with several completely wiped off their foundation. When the tornado was all said and done 3 people were killed with hundreds more injured.  The 3 causalities made this the first killer tornado in the state of CT since the killer Wallingford tornado of 1878.  It is also believed the Windsor Locks tornado is the strongest tornado to hit the state in modern history and may only be rivaled by the 1878 Wallingford tornado.  The tornado caused more than $200 million in damage in 1979 USD (that works out to be about $640 million in today's money!).  To this day the Windsor Locks tornado which received a rating of a strong F4 still ranks as the 9th most costliest tornado in recorded history.  This was also the first tornado to be ranked this high on the Fujita scale since records had been kept beginning in 1950.

All in all you would never expect to get such a damaging tornado from this system.  Normally you'd see weak tornadoes (which there were a few in PA/NJ earlier on in the morning) but to expect such a strong tornado would be nuts.  While wind shear was certainly impressive along with helicity it is believed that just a little bit of heating just prior to the storm helping to boost up instability along with terrain enhancement (the storm was moving due south to north through the CT Valley and low-level winds usually are enhanced in valleys) helped to create an environment that was perfect enough for the developed of a violent tornado.  The supercell thunderstorm which was moving left to the mean wind flow "left mover" also helped for the storm to further utilize the strong wind shear in place yielding to even locally higher amounts of helicity.  Besides this F4 tornado there has been one other tornado ranked as an F4, that occurred on July 10th, 1989 and moved through Hamden, CT and diminishing just prior to hitting downtown New Haven.  Although this was rated as an F4 it is believed that this tornado was actually weaker than this.  To this day, the Windsor Locks tornado remains king for deadliest/strongest tornado in modern history to hit CT but going back in history it still sits below the great Wallingford tornado of 1878.

Another potent late fall-like system to affect the Northeast 9/18/12

Yet another rather intense weather system is expected to affect much of the Northeast and mid-Atlantic states tomorrow as an unseasonably strong cold front will once again interact with a fairly warm and very moist airmass.

A rapidly deepening trough will be working eastward through the eastern United States dragging a cold front along with it.  At the same time an area of surface low pressure is expected to develop across the TN Valley region and work northward along the cold front swinging a warm front northward.  Computer models are generally in agreement that this warm front will lift northward through the NYC area and then stall across central CT.  South of the warm front the airmass will become very moist with dewpoints potentially rising into the lower 70's as far north as the NYC area and even into portions of southern CT.  North of here dewpoints will be into the mid and upper 60's.  Where the lower 70's dewpoints occur this will yield to an airmass which will become marginally unstable.  Computer forecast models develop anywhere between 500-1000 J/KG of MLcape.

Wind fields aloft are expected to become quite strong for this time of year.  Computer models are generating a 45-55 knot low-level jet working into the region, however, computer models have slowed down on the timing of the core of this jet getting into southern New England.  The mid-level jet is expected to increase to 60-70 knots with a 80-90 knot ULJ moving nearly overhead as well.

The combination of modest instability along with very strong wind fields aloft will yield to the potential for some strong to even severe t'storms tomorrow and there will be two storm modes we may have to deal with.

1) With the northward movement of the warm front the potential will exist for isolated low-topped supercells to develop.  Very similar to what we saw occur last Saturday where two confirmed tornadoes were confirmed in the NYC area.  This potential is dependent on how buoyant the boundary layer can become and how much instability can develop.  Where dewpoints get into the lower 70's this would be enough to yield a very buoyant boundary layer and be enough to create modest instability.  The best potential for this will likely be from NJ up through NYC area and into extreme southwestern portions of CT.

2) Narrow low-topped squall line associated with the cold front.  Extreme forcing along the front and a moisture rich airmass is expected to lead to the development of a very narrow low-topped squall line.  While thunder/lightning may be limited this line could be strong enough to bring down some of those stronger winds aloft yielding to a threat of damaging winds.  This line would move through eastern NY/southern New England probably after 9-10 PM.

With the main piece of shortwave energy expected to move north-northeasterly this means eventually the developing line will begin to ourtun the stronger forcing and dynamics aloft.  We actually saw this occur last Saturday as well which was a main reason for the line rapidly weakening as it approached southern New England.  As this line moves through central/eastern PA into SE NY and towards southern New England it will once again weaken.

With such strong winds aloft tomorrow and just above the surface tomorrow will be quite breezy as well, even without shower/t'storm activity.  Winds could gust as high as 30-40 mph region wide with the strongest winds occurring across the coast and areas above 1500'.  In fact, for elevations above 1500-2000' winds at the peak of the event could gust as high as 60-70 mph...perhaps even upwards of 80 mph!  This will likely happen across the Berkshires and into the Green/White mountains of VT/NH!

Torrential rains will be likely tomorrow as well and this could lead to pockets of flash flooding.

Below is a graphic indicating areas of greatest wind and severe weather potential.

Saturday, September 8th, 2012 severe weather threat

Severe weather across this part of the country starts to become less uncommon as you move through August and into September, however, we are by no means immune to it!  A developing and strengthening storm system will provide us with the potential for some strong to severe thunderstorms on Saturday along with some torrential rains.

A sharpening and deepening trough will slide eastward dragging along a cold front with it.  At the same time an area of surface low pressure is expected to develop and rapidly intensify as it moves northward from the Tennessee Valley through western PA/NY and into southern Canada.  This will allow a warm front to move northward through southern New England allowing for an unseasonably warm and moist airmass to advect into the region.  Even with limited sunshine tomorrow temperatures should range from the upper 70's to lower 80's with dewpoints creeping perhaps into the lower 70's.  This combination of warm temperatures and high dewpoints will lead to at least a marginally unstable airmass.  some computer models are indicating the possibility of several breaks of sunshine tomorrow across the entire region.  if this does occur and we can get a period of strong solar heating than the possibility of moderate instability will exist.

A piece of powerful shortwave energy is expected to round the base of the deepening and strengthening trough.  With the shortwave interacting with the trough we will see winds aloft increase.  Computer models are forecasting a low-level jet in excess of 30-35 knots with a mid-level jet of 45-55 knots and an upper-level jet streak of 90-100 knots placing the region in the right entrance region of the upper level jet.  Computer models are also forecasting a great deal of helicity thanks in part to directional shear in the lowest 2km of the atmosphere and strong speed shear.

Given the presence of strong forcing/lift associated with the cold front and approaching trough and the potential for at least weak instability a squall line is expected to develop just out ahead of the cold front.  Given the presence of very strong winds aloft, strong atmospheric mixing, and no inversion in the boundary layer this squall line would have the potential to produce strong to even damaging winds from it's entire journey from NY/PA all the way to the New England coastline.

We will have to keep an eye out for any discrete storm development out ahead of the main line as well.  Given the presence of high helicity and long/curved hodographs as observed on skew-t soundings if enough instability materializes the potential will exist for isolated tornadoes as well.  This threat could be further enhanced across the Hudson Valley of NY extending into southern VT as well as the CT River Valley.  This potential will be monitored extremely closely.

If discrete development does develop it could happen as early as 3-4 PM with the main line moving through during the late evening and early overnight hours.  While instability will decrease with the loss of daytime heating storng dynamics and forcing should help to sustain the line some as it gradually weakens with eastward progression, however, still possessing the threat for strong winds.

Given the presence of high dewpoints and lots of low-level moisture torrential rains will be likely as well, potentially leading to pockets of flash flooding.

While the entire region will be at risk for strong to severe storms the area with the greatest potential will be from eastern PA/NY extending into southern VT and through central CT/MA.

***Significant Widespread Severe Weather Outbreak Likely Across Parts of the Northeast into Western Southern New England 7/26/12***

Several computer forecast models are coming into agreement that a fairly significant widespread severe weather event will unfold tomorrow across portions of the Northeast extending into western southern New England.  The potential for destructive winds, extremely large hail, and perhaps tornadoes are all possible from central PA to SE NY/N NJ and extreme western MA/CT.

An approaching mid/upper level trough which is not all that well defined will be sliding eastward.  Associated with this trough is a surface area of low pressure and a pretty strong piece of shortwave energy.  As the trough approaches weak height falls will begin to occur and the surface area of low pressure will initially be further deepening.  In response to the weak height falls and some continued deepening of the surface low early on, a warm front will be lifting northward and finally stalling out somewhere around the VT/NH/MA border.  South of the warm front a very warm and very moist airmass will work into place.  Dewpoints will be climbing through the mid to upper 60's...possibly even getting to 70F or a few ticks higher!  With 925mb temps climbing between +22C and +25C and 850mb temps climbing to around +20C full sunshine and full mixing would yield surface temperatures in the mid to upper 90's.  It appears likely there will be some cloud debris to begin the day and b/c there are uncertainties to how quickly we will get rid of these clouds we will likely not achieve maximum heating.  However, we should yield enough sunshine for temperatures to get into the mid to upper 80's...perhaps even some lower 90's across NE PA/SE NY/N NJ where cloud cover initially may be much less of an issue.

Some computer forecast models also are hinting at an elevated mixed-layer plume to advect into the region from the upper Mid-west and some forecast soundings to verify this.  It is very interesting to note, however, this elevated mixed-layer plume is actually located a bit more shallow in the atmosphere compared to where we normally see them located.  Normally with elevated mixed-layers you will find them from about 800mb up through 550mb or so.  This elevated mixed-layer plume looks to exist from about 850mb up to only 700mb or so.  Since elevated mixed-layers are associated with some pretty dry air it's preferred to have them located a bit higher aloft b/c this keeps the dry air toward the mid-levels of the atmosphere and keeps the low-levels of the atmosphere very moist.  Having the elevated mixed-layer plume this shallow could allow for drier air to end up mixing into the lower levels of the atmosphere drying things out a bit which could reduce low-level instability.  Given how the low-level flow is expected to be from the southwest and remain southwesterly this should keep a belt of strong moisture flowing into the lower levels preventing the drier air from working in.  The elevated mixed-layer plume being so shallow may also lead to some fairly poor lapse rates in the 700-500mb level.  Normally with elevated mixed-layers you have very steep >7-7.5 C/KM 700-500mb lapse rates as temperatures from 700mb to 500mb drop fairly significantly.  With the elevated mixed-layer plume so shallow the difference in 700mb and 500mb temps my not be as good as they normally would be, however, computer models continue to show that lapse rates here should still be on the order of 6.5-7 C/KM.

With the approaching trough/surface area of low pressure progged to be sub 1000mb and strong piece of shortwave energy wind fields aloft will also vastly increase and we will be dealing with dynamics we'd typically in the early spring or fall months.  Computer models are forecasting a low-level jet in the 925/850mb levels to be on average about 20-30 knots coming in from the southwest...helping to keep funneling in low-level moisture.  The mid-level jet at the 700/500mb levels is also expected to increase to as much as 35-40 knots at 700mb to 45-55 knots at the 500mb level with winds here turning to a more westerly direction.  The region will also be in the Right fornt quadrant of a 85-90 knots upper-level jet max with upper level winds over the region of about 50-60 knots coming from a more westerly/west-north-westerly direction.  500mb wind speed values of 45-55 knots should yield to about 35-45 knots of vertical shear.  With all this said there will be a great deal of both speed and directional shear present.  We will also have to watch surface winds across the region, especially the valley locations where surface winds may back to the south or even south-south-east thus further increasing helicity, especially in the 0-1km and 0-2km level.  The presence of speed/directional shear will also yield to large amount of helicity with 0-3m helicity forecasted to be in the 200-400 m2s2 range and 0-1km helicity in the 150-300 m2s2 range.  This is VERY favorable for supercell t'storms as well as tornadoes.

With surface temperatures expected to climb well into the 80's with dewpoints nearing 70F under the presence of an elevated mixed-layer plume with 700-500mb lapse rates on the verge of 6.5-7 C/KM the potential for moderate instability to develop is there.  In fact, several computer models are generating as much as 2500-4000 J/KG of SBcape, 1500-3000 J/KG of MLcape, 2000-3000 J/KG of MUcape, LI values of -6C to -9C and Ncape values as high as 0.25.  This is all indicative of a moderately unstable airmass.

During the morning hours as the warm front lifts northward showers/t'storms are expected to develop as isentropic lift increase as well as low-level warmth and moisture leading to an increase in elevated instability.  In fact, a mesoscale convective system is possible.  Some strong to localized severe storms are possible with this feature as it's moving through.  After this complex, if one develops moves through the question then will become how quickly can we get rid of the cloud debris and how quickly can we receive sufficient heating to rapidly destabilize the atmosphere to achieve those instability values just lifted above?  It does appear that we will indeed clear out the cloud debris and by early afternoon we see sufficient heating allowing for a rapid jump in temperatures/instability.  Once this occurs we should begin seeing the development of t'storms; first across PA/NY and moving towards southern New England with further development expected there.


Several rounds of severe weather are expected tomorrow and lasting well through the evening and overnight hours as the front slowly drags eastward.  Early on in the afternoon through the early evening hours numerous supercell t'storms will be possible with the threat for destructive winds, very large hail as well as tornadoes.  Once we near evening and near sunset we start losing those stronger helicity values  and the severe threat should shift from tornadic supercells to bowing squall lines capable of destructive winds and large hail...an isolated tornado with these can't be ruled out either.  Torrential rains will also occur with any storm as well as vivid cloud-to-ground lightning.  Flash flooding will also be possible.  


Everyone is strongly urged to pay extremely close attention to updates and latest forecasts throughout the day and take each and every warning extremely seriously.  This is no run of the mill typical Northeast severe weather event and we have a much higher than normal threat for severe weather with the potential for tornadoes.  


Below is a graphic displaying the areas with severe weather potential and areas of heightened potential:

Active weather week on tap (7/23-7/27)

If you love low humidity than this past weekend was just for you.  After an intense round of t'storms moved through southern New England on Wednesday a much direr airmass has settled into southern New England. This is all about to change.  A developing southwesterly flow is working to bring in a much warmer and more moist low-level airmass into the region.  In fact, dewpoints across the region are slowly beginning to work their way into the lower 60's and by tomorrow mid to even upper 60's dewpoints will have worked into much of the region and by Tuesday we could be looking at dewpoints approaching 70F!  With a warmer low-level airmass moving into the region as well temperatures both Monday and Tuesday should reach the mid to upper 80's and possibly 90F in the hottest locations.  With the increased humidity and moisture the threat for t'storms will also increase and both Monday and Tuesday feature interesting potential across southern New England.  We will take a closer and more detailed look at each individual day.

Overnight Sunday into early AM Monday:

As dewpoints continue to increase through the evening and overnight period and PWATS increase as well we will begin developing some elevated instability across the region.  In fact, a few computer models also develop some fairly weak surface instability overnight into early AM.  Later on this evening/overnight computer models are showing a weak piece of shortwave energy moving through aloft in the mid-level flow.  Given the presence of developing elevated instability and perhaps some weak surface instability some showers and perhaps a few t'storms are possible during the overnight and early AM period.  Winds aloft are on the weak side and mid-level lapse rates aren't particularly steep and with not much in the way of instability severe weather is not expected overnight.  Any storm though will of course carry a lightning risk along with torrential downpours given the increasing moisture.

Monday afternoon/evening:

Several computer models are developing a lee trough just to the west of southern New England during the late morning and early afternoon hours.  With surface temperatures into the mid to upper 80's, dewpoints into the mid to upper 60's, and mid-level lapse rates around 6.5 C/KM the atmosphere may become moderately unstable tomorrow afternoon.  While initially winds aloft are on the weak side and mid-level lapse rates won't be particularly steep both do increase as the afternoon goes on.  By the afternoon mid-level lapse rates should be between 6.5-7 C/KM with deep layer shear increasing to around 30-35 knots by late afternoon/early evening.  Some models also develop a LLJ across the region which helps to increase low-level shear and helicity.  At this point it's a bit unclear as to exactly how tomorrow will unfold, however, given some of the pieces in place some thunderstorms are possible tomorrow afternoon and evening.  Given some of the favorable parameters some strong to severe storms can't be ruled out.  Some simulated radar models actually develop a squall line by late afternoon and move it through western CT late tomorrow evening so this will have to be watched.  While the main threat should be torrential downpours/isolated flash flooding given the presence of high moisture damaging winds and large hail are also possible in some of the stronger storms.

Tuesday:

Tuesday appears a bit interesting although it appears we will dodge what could be a much more widespread and significant severe weather outbreak.  Over the past few days computer models continue to be faster with the frontal passage and move the cold front through much of the region by mid to late morning.  Due to this winds in the boundary layer shift from southwest to a more westerly/northwesterly direction and we start drying out the mid levels of the atmosphere and this dry air mixes down to the lower levels thus preventing stronger instability from developing.  Shear/lapse rates are expected to be fairly impressive on Tuesday as well.  While a major chunk of southern New England looks to miss out the potential for severe weather may still exist across eastern MA as the front may not move through here until mid-afternoon or so.  This would allow for this area to destabilize much greater and have a great combination of strong winds aloft/instability.  It's possible eastern MA could see quite a decent severe weather event.  We'll still have to closely pay attention to this though as if the front does slow down by several more hours this could increase the threat for severe weather for areas further west.

After Tuesday all eyes turn to Friday as some computer models have a fairly impressive setup for severe weather across New England.  However, given this is still several days out and alot can change we won't get into the details now.  We'll worry about tomorrow and Tuesday first but it does appear to be an active week coming up.