Thursday Storm Update

Yesterday I had made a snowfall forecast and I'm just going to be flat out wrong, especially down across CT.  I jumped the gun too quickly and should have never made an initial forecast with snowfall amounts that high.  It was virtually irresponsible thinking on my part and knowing the red flags I should have been more conservative with my amounts.  Typically when going on the heftier side of amounts, I like to see a tremendous amount of consistency and agreement within the data and that was not the case.  With this said I will be reducing what I am expecting in terms of totals.  

When composing my initial forecast I thought there was credibility that we would see the system really strengthen off the NJ coast and continue to do so as it pushed up to the north and east.  While this would have initially pumped in some warmer air, the rapid strengthening would have led to dynamic cooling which would have quickly cooled the atmosphere and we would see a quick change back to snow and heavy snow.  This scenario, however, does not look like it will happen.  Instead, what we will see if the system strengthen as it's moving up along the SE MA coast and this will mean a massive snow event for a good part of northern New England.  

The highest snowfall totals look to occur across western portions of MA, perhaps down into extreme NW CT.  This is where the latest NAM and GFS computer forecast models indicate this is where the most intense lift will occur.  In this area during the height of the storm, snowfall rates could approach 1.5''/HR and perhaps even as much as 2'' per hour:

Down across the state of CT with the system tracking very close to the coast and no high pressure to the north to secure cold air in the lower levels of the atmosphere and down at the surface we will see warm air quickly surge into CT.  Colder air will remain in place a bit longer across NW CT and the hills of NE CT and this is where the higher totals will occur in the state.  

As the main surface low passes pretty much over CT and tracks northeast, it will begin to strengthen and a closed off circulation develops over the state of RI, this track will mean warmer air also surges northward into east-central and eastern MA so these areas will begin to transition over to rain as well.  West-central and western MA should remain mainly, if not, all snow and this area will receive the higher amounts.  

Down across CT, precipitation will begin between 9:30 AM and 10:30 AM and outside of the southern part of the state, precipitation will start off as snow and quickly change over to rain.  Expect precipitation to begin across RI and MA in the late morning to very early afternoon hours (developing from the SW first and working NE).  Winds will also become strong as well, especially across MA and perhaps RI as well where gusts of 45-55 mph will be possible leading to isolated pockets of power outages.  The precipitation begins to taper off across CT during the early evening hours and it is possible that the precipitation may even end as snow across parts of northern CT.  This could lead to an additional inch or two across some parts.  Across RI and MA everything begins to taper down during the mid-to-late evening hours.    

Below is my updated snowfall map...yes a far cry from what I was expecting yesterday afternoon:

Major Storm Expected on Thursday

We are tracking yet another storm system to impact southern New England during the day on Thursday lasting well into the overnight hours but there continues to be some uncertainties within the computer forecast models and that does lead to a challenging forecast at this time.  A couple of our computer forecast models are in agreement that as the system works up just off the coast that it will undergo rapid cyclogenesis (strengthening) and become quite a powerful storm.  Meanwhile, some other computer forecast models aren't as impressive with the system and have a much weaker and faster system.  If this isn't tough enough there will be a bit of uncertainty as to exactly where the rain/snow transition line pivots and this is critical because it could mean the difference between only maybe 1-2'' of snow and perhaps as much as 6-7'' of snow.  These details should be ironed out over the next 24-36 hours.

Both the NAM and European computer forecast models are actually in fairly good agreement with each other on a rapidly intensifying storm system just off the coast.  Unfortunately I am not able to post Euro images, however, I can go ahead and post some graphics from the NAM.  The 12z run of the NAM from the 27th of December shows a very strong piece of shortwave energy just south of southern New England by 7:00 PM EST Thursday evening:

The forecast is for this piece of shortwave energy to continue pushing to the northeast and undergoing further and rapid strengthening.  The image below is a forecast for 1:00 AM Friday morning:

This will allow the entire system t rapidly strengthen so the response will be a rapidly deepening surface low pressure and closed off circulations at 925mb, 850mb, and 700mb:

In comparison, the GFS computer forecast model valid for the same forecast time shows a weaker system than the NAM and Euro and actually doesn't really begin to strengthen the system until it reaches the Gulf of Maine. Also note how much quicker the GFS is than both the other models:

Each of these forecasts presents a different set of solutions that we could potentially see.  The GFS forecast model also tracks the system pretty much over southern New England.  What this does is allow much warmer air to work into much of the region within the lowest 3,000-4,000' of the atmosphere.  This would eventually lead from a transition from snow to sleet/rain across many locations, particularly south and east of the MA Pike.  The NAM, on then other hand, also brings in some warmth ahead of the system.  This is due to the fact that it rapidly strengthens the system well to our south and since the track is tucked closer to the coast warm air floods in ahead of the system.  However, as the system rapidly intensifies and develops those closed off circulations (and the track is just to our south and east), this induces what is called dynamic cooling and will help to rapidly cool off the lower levels of the atmosphere.  This would mean MUCH more snow for a larger chunk of the region (with the exception of the south coast where the track would still drive in warmer air here).  This is what we need to watch over the next 24-36 hours.

One thing presented on all models is the possibility for a period of moderate to heavy precipitation (whether it be snow or rain).  The GFS has a much shorter window for this probability than the NAM or Euro.  Taking a look at some bufkit profile soundings from the 12z NAM for a few select locations across southern New England we see

1) Snnowgrowth zone positioned right between 12,000 and 18,000' (purple/yellow contours)
2) Strong upwards vertical motion present within this zone (the red contours with negative values)
3) -15C temperature contour crossing through this zone (thin yellow line running horizontally)
4) High relative humidity values within this zone (not shown below as it would look too "messy")

All four of these combined indicate that the potential exists for moderate snowfall accumulations to occur for any areas that remain all or mainly snow.  The NAM shows INCREDIBLE upwards vertical motion across eastern portions of southern New England including the Boston area:

If the NAM/European computer forecast models are correct we would see a very intense band of snow setup just to the northwest of the tracks of the 925/850/700mb lows and this is where the axis of the highest snowfall totals would occur.  Snowfall rates could approach 1.5'' per hour and we would also be looking at the potential for strong winds as well with gusts as high as 40-50 mph.  Given the degree of lift and even some weak instability thanks to presence of steep mid-level lapse rates, some thundersnow can't be ruled out wither which would locally enhance snowfall rates as well.  If the GFS is correct we would be looking at a much weaker system across southern New England with not as much impacts.  Northeastern MA into northern New England would now see the higher impact as the system strengthens as it moves into the Gulf of Maine.

As of right now, given the consistency of the Euro/NAM thus far and the GFS has seemed to trend a bit in the direction of the Euro/NAM, I am leaning more towards a solution depicted by the NAM/Euro.  This of course can easily change as if they are too quick with the strengthening of the system we see higher likelihood for warmer air to invade.  So this what I'm expecting:

• Snow begins in the mid-to late morning hours, especially across CT and parts of RI and early afternoon the further north into MA one goes.  
• Snow may transition over to rain briefly, especially the south coast, as warmer air initially moves in ahead of the strengthening system
• Rain will then begin to transition back over to snow as the system strengthens and dynamic cooling cools the atmosphere aloft.  The coast, however, will remain more rain
• There will be a zone through the system as well in which snow transitions between sleet and perhaps some freezing rain.  This will be the cutoff between the higher and lower snow totals
• During the height of the storm winds could increase to 40-50 mph causing isolated pockets of power outages
• Snowfall rates could approach 1.5'' per hour and perhaps as high as 2'' per hour if there is any embedded thundersnow 
• The precipitation begins to taper off during the overnight hours of Thursday into Friday.
• Thursday rush hour commute looks to be very bad so expect a very slow commute with numerous delays.  

Below is my initial snow map but there is not a high amount of confidence with this due to concerns mentioned above.  Typically I would be more shy than not in going with lower snowfall totals, however, when the NAM and Euro tend to be in agreement more times than not that is a very good indication of what will verify.  This doesn't always work but as of right now I would lean this way:

Active Weather Period Over the Next 96-Hours

We are in store for one helluva roller-coaster ride weather wise over the next 96-hours and that ride begins well as I speak.  A powerful Arctic cold front is set to push through southern New England later on this evening and as this front plows through temperatures will really bottom out as lows tonight will be in the single digits to around 0 and even maybe slightly below-zero in some spots and that's without the wind chill.  While it has been quite gusty today the core of the strongest winds have yet to arrive.  There are some differences within the NAM computer forecast model and GFS forecast model as to what the higher end of the wind spectrum may be, however, both models are very impressive with the maximum wind gust potential.  Looking at some bufkit soundings from the latest afternoon run of the 4km NAM model across some selected locations across southern New England (Windsor Locks, CT, Worcester, MA, and Chatham, MA) the 4km NAM is suggesting that the maximum wind gust potential could be as high as 70-80 mph late this evening.  With this range we are talking about minimal category one hurricane-force gusts.  The NAM also has the profile mixing nearly dry adiabatically up to about 9,000' (~700mb) which is incredibly impressive.  Given how this may be a tad overdone and we have to consider friction, the extend of these winds are possibly a bit too high, however, 65-75 mph wind gusts are certainly possible and this is what the GFS model indicates for highest gust potential:

(NOTE:  I only showed 18z NAM bufkit soundings...even though the winds atop mixing layer are probably overdone b/c this was latest data available as 18z GFS bufkit was not out)

With winds increasing further this will not only set the stage for the possibility of scattered to numerous wind damage (downed trees/limbs and power lines) but with temperatures dropping further we will be looking at very dangerous wind chill values which could be as low as -10F to -20F.  Values these low can lead to frostbite in a short amount of time for any exposed skin.

While high temperatures on Friday will be much colder than today (not getting out of the teens in many locations) the winds will not be as strong as today, however, gusts could still get into the 20 mph range and we will once again deal with near dangerous wind chill values (as low as -10F).

One other note of interest with this brutal Arctic airmass is how close to the ground the stratosphere will be.  This point-and-click forecast sounding for a location in western MA for about 10:00 PM tonight morning shows the tropopause (layer which separates the troposphere from the stratosphere) being only around 9,000'-10,000ft off the ground...very impressive for these parts:

This brutal Arctic cold blast will be quite short lived, however, as late Friday night into the early part of Saturday our next weather system begins to impact the region.  Like with last Sunday into Monday we will once again see a developing storm system track well off to our north and west and this means we will eventually warm things up (and actually quite substantially) but before that happens we will have to deal with quite the wintry mess.  We are looking at accumulating snows for pretty much everyone (with the further north you go into southern New England the higher the potential totals) before everyone eventually transitions over to some sleet, freezing rain, and then some rain and then temperatures begin spiking up all the way into the 40's, 50's, and maybe even near 60F in some spots before the cold front pushes through Sunday night and some much colder air filters back in.

Given the extent of the airmass we will have in place it will take some time to really get the surge of warmer air into the region, thus we will begin as snow.  As always with these setups, the biggest question is how quickly does the warm air move in and how much precipitation falls as snow?  By 7:00 AM EST Saturday morning some shortwave energy moving through the jet stream aloft will be just off to our west which will help enhance the degree of atmospheric lift.  At the same time we'll have the main surface low pressure well off to our west across the Ohio Valley region:

  Due to the fact there will be no amplification of the jet stream/short wave energy (the short wave energy is also not really consolidated and compact) the system isn't expected to strengthen all that much and most of it's strength will really be from the influx of warmer/moist air from the Atlantic Ocean and cold dry air working around the backside of the system (creating a good thermal gradient which helps these systems intensify) so we aren't really looking at a powerful system.  In fact, the system may begin to weaken which will ultimately shut down the influx of warmer/moist air into the storm and the precipitation will begin to "shut off" and the axis of heavier precipitation moves off the coast:

Region wide temperatures will be certainly cold enough for precipitation to begin as snow and the first flakes should begin to fall during the overnight hours of Friday into Saturday (between 1:00 AM and 4:00 AM).  There will be some dry air in place initially, however, the profile will begin to saturate rather quickly.  As we move through the early part of Saturday morning some stronger atmospheric lift will push into the region and with this we will see periods of moderate to perhaps even some heavy snows.  At the highest snowfall rates may approach 1'' per hour and given we are looking at snowfall rations perhaps as much as 15:1 the snow will be quite fluffy and will accumulate rather quickly.  Looking at some bufkit profiles for a few locations across southern New England, initially snow growth may not be the greatest but they quickly become better (you want the yellow contours to be right between about 12,000-18,000ft with the -15C isotherm running through it ).  This is great for developing those fluffy flakes.  The next thing you want is to be able to lift parcels/moisture into this region and for that we look for those thin red contours (omega) which indicate vertical lift.  The more contours (and negative the number) the greater the lift.  Looking at these soundings we do have some red contours intersecting this great snow growth zone, however, not a great deal of red contours.  While lift will not be extremely heavy (this will preclude rates exceeding 1'' per hour) it will be sufficient for a period of moderate to perhaps heavy snow:

By early afternoon, however, much warmer air begins to filter into the region and as this warming occurs we will see a transition from snow to sleet/freezing rain, then rain beginning from south to north:

With all this said this is what I am expecting for snow.  Keep in mind that mainly everyone south of the MA Pike (and even a bit north of the Pike) will eventually transition over from snow to rain.  While some areas will see some freezing rain this should be be a major concern as the stay will be brief:

We aren't done just yet!  As Saturday progresses, we will continue to see a very strong push of warm-air advection, both at the surface and in the lower-levels of the atmosphere.  In fact, overnight Saturday into Sunday temperatures about 5,000' off the ground will be approaching the 50F mark and we will feel this warmth at the surface as well with temperatures rising into the 40's/50's and maybe near 60F in spots by 7:00 AM EST Sunday morning:

This warmth arrives just ahead of another cold front which will push through sometime mid-to-late afternoon.  With the warmth, however, just ahead of the cold front we will deal with yet another period of moderate to perhaps even heavy rain and we can't even rule of a thunderstorm as well, especially if some low-level instability develops thanks to the surge of warmth/moisture in the lower-levels of the atmosphere.  Once the cold front passes through we are back towards cold temperatures with overnight lows Sunday into Monday back into the teens/20's and high's on Monday only into the 20's.  This is certainly going to be a roller-coaster of a ride and certainly some active and very interesting weather!

Active Weather Pattern Continues With Arctic Blast

We have certainly entered a much more active weather pattern as of late and this looks to continue.  As we move through the next week not only will the weather pattern remain quite active but it will be rather bumpy with some pretty significant temperature trends.

First off, we will have a weak storm system which will affect southern New England tonight.  An area of low pressure will be developing off the coast of the mid-Atlantic and slide to our south and east.  At the same time an upper-level shortwave trough will be passing by off to our northwest.  This scenario will set the stage for some light snow showers, especially down across CT during the evening/overnight hours.  No accumulations are expected, however, some areas could get a coating of snow, especially if the low tracks a little further north.

Perhaps the biggest story over the next several days outside of the storm potential on Saturday will be extreme cold for this time of year.  An arctic cold front is expected to pass through southern New England late Wednesday evening and may be accompanied by some snow showers.  This will usher in some more cold air.  However, on Thursday a much stronger secondary cold front pushes through the region and this will usher in some extreme cold for this time of year.  While Wednesday night and Thursday will be quite cold, we feel the brunt of the cold Thursday night, Friday, and Friday night ahead of the next storm system.  In fact, computer forecast models are forecasting temperatures at 850mb (around 4500-5000') to be around -20C to -30C 7:00 AM EST Friday morning.  That is quite exceptional for this time of year:

This will yield overnight lows Thursday into Friday down into the single digits and perhaps even below-zero across the typical coldest locations.  Highs on Friday may even struggle to get out of the low 20's across many places and some spots could fail to reach 20F.  In addition to this cold we will have to deal with some pretty strong winds as well so windchill values will make it feel like it is well below-zero at times.  By Saturday things begin to change ahead of our next weather system and that looks to pose a bit of a mess, perhaps similar to what we dealt with Sunday night into Monday.

An area of surface low pressure associated with some shortwave energy will be tracking across the Great Lakes late Friday into Friday night.  As this occurs, a warm front will begin pushing northward towards southern New England.  As the warm front approaches we will see an increase in isentrpic lift associated with the warm front.  There are questions, however, with how much moisture we will have in place as the airmass will be quite dry, however, computer forecast models do show some saturation of the atmospheric profile so we may see a period of light snows develop overnight Friday.  Given how cold the airmass and ground will be snow will have zero problem sticking.  Given how the snows will be low-level produced the flakes should be tiny and we won't see heavy snowfall rates so these won't produce any big totals (maybe 1-2'').  The initial surge of warm-air advection at the surface may be rather slow through the first part of Saturday.  This is due to the possibility of a wave of low-pressure developing along the warm front:

Given how extreme the cold will be in the lower-levels of the atmosphere the warm-air advection early on will be rather weak as well until the low-level jet begins to increase and that will really accelerate the northward progression of much warmer air.  This is huge because this means a much longer time of the atmospheric profile being cold enough ti support snow.  With this in mind, while it is too early to throw out snowfall totals, many areas may be able to pick up at least 3-4'' of snow before we begin seeing a transition to sleet, freezing rain, and then plain rain.  Areas north of CT into MA have a much higher potential to pick up at least several inches of snow.  By early afternoon the low-level jet at 850mb is expected to reach 50-60 knots and this will vastly work to usher in much warmer air, both at the surface and in the lower-levels of the atmosphere:

 

As we move into Sunday things are looking rather interested ahead of the cold front associated with the low pressure system tracking across the Great Lakes  The surge of warmth ahead of the cold front looks quite impressive and temperatures could soar into the 50's to perhaps near 60F overnight Saturday into Sunday.  Computer forecast models suggest temperatures at 850mb will approach +10C very early Sunday morning:

 
This warmth will be very short lasting, however, as the cold front begins moving through during the late morning/early afternoon hours.  With the approach of the cold front we could see a period of heavy rainfall and perhaps even some thunder.  Once the cold front passes through temperatures will fall back very quickly as lows Sunday night into Monday will only be in the teens across the region.

We will certainly be experiencing some pretty drastic swings in the weather over the next week, especially with regards to temperatures.  For snow lovers, its very unfortunate the cold isn't producing snow, however, this is due to the fact that all the storms are tracking well west of us and that is allowing for warmer air to move in ahead of the storms.

Looking long-term there are growing signs that as we approach the Christmas holiday and first part of 2017 we will see a major shift in the overall hemispheric weather pattern and we may enter an average to even much-above average regime temperature wise.  This doesn't mean we won't see any sporadic cold shots but does mean overall we will be much warmer.  This certainly won't be good news for snow lovers.

Over the next few days as we approach the weekend we should be able to pin down details as to what to expect snowfall wise, whether we'll have issues with freezing rain, and when things transition over to rain.

Quick Storm Analysis

I will say I am pleasantly shocked that some snow has already began to fall across parts of CT and started as early as 2-3 PM.  Granted it was very light snow and tiny flakes but still indeed snow.  My main concern was the dryness of the atmosphere and how long it would take for the atmosphere to saturate .  Taking a look at a forecast sounding from the 4:00 PM EST (21z) run of the RAP computer forecast model timed for about 7:00 PM EST the atmosphere certainly becomes quite close to saturated from about 525mb down to the surface (note how the dewpoint (green) line and temperature (red) line are pretty much touching:

The snow that has been falling is related to the system, however, it's not necessarily from the system.  I say this because the focus of lift is completely different.  The snow which has fallen thus far has been the product of at least these two factors; 1) warm-air advection in the lowest levels of the atmosphere and 2) enhanced low-level lift from the nose of the 850mb jet:

Thanks to a very cold airmass in place and quite the cold ground, despite the fact the snow is falling very lightly and the flake size is very tiny (this is more like snow grains!) it is sticking.  In fact, some areas have a coating on the ground, including at Westside Campus at Western Connecticut State in Danbury, CT!  If there was more in the way of mid-level lift to lift parcels into the mid-levels of the atmosphere we would be seeing beautiful dendrites and big fluffy snow flakes.  Looking at the same 21z RAP we see very good dendritic snowgrowth right in the favorable area for snowgrowth (between -12C and -18C) with the -15C isotherm running right through this zone.  When you have these ingredients in place you get your perfect snowflakes which are big in size and these are the ones that accumulate quickly.  The only issue is there is no lift in this zone.  For upward vertical motion we want to see red contours but we do not have those present into this zone thus we aren't lifting air parcels or moisture into this zone so the end result is these little tiny snowflakes:

Currently the area of surface low pressure which is the main aspect of the system is still well off to our  west over the Ohio Valley region.  This low pressure will continue to strengthen but slide off to our north and west and with this track we will continue to see warm-air advection occur and warmer temperatures filter in.  Until then we will continue to see some snow and later on this evening/early overnight the flake size should increase as stronger mid-level lift slides in.  However, the timeframe for this bigger flake size and heavier snow rates will be brief (especially in CT) and snow totals will be down here.  I see no reason to make any changes to my map fro Friday night:

Sunday night/Monday Storm Update

Confidence continues to increase on another storm system hitting southern New England Sunday night and lasting through much of Monday.  However, latest trends indicate that the further southward you go in southern New England, the less in the way of snow you will see.  While we have a very cold airmass in place currently the storm tracking to our north and west will allow for a strong surge of warmer air to work into the region ahead of the storm.  With this many locations (especially south of the MA Pike) will see a quick transition to sleet, freezing rain, and even plain rain.  While I believe this is the more likely scenario, we can't completely rule out the possibility of more in the way of snow even further south in CT (away from the coast).  This will ultimately depend on the overall strength of the storm and there are some differences within the computer forecast models.

Both the NAM and GFS computer forecast models develop a fairly strong surface low just off to our north west and develops closed off circulations at 925mb, 850mb, and even at 700mb (to a degree).  This is a sign of a rather intense system.  With these lows also tracking to our north and west and with the system so strong it will yield a very strong southerly flow into the region which will bring a surge of much warmer air northward into our region both at the surface and lowest several thousand feet of the atmosphere:

The below images are from the GFS computer forecast model, however, the NAM model is similar

 
Unfortunately I am not able to post Euro graphics, however, the Euro model is far different than the GFS and NAM.  The Euro is not as intense with the system and doesn't really developed closed off circulations at 925mb and 850mb.  This would support less in the way of warm air advection meaning the colder airmass sticks around much longer and this would yield more snow.  This solution can't be ruled out, however, I don't think it is very likely.

There are also questions with regards to the exact timing of the precipitation.  While the front edge of the precipitation may be entering into CT by as early as 8-10 PM the air is still going to be be quite dry so initially the precipitation will evaporate before reaching the ground.  The air may not become saturated enough until close to midnight.  This evaporation and dry air will do a few things; 1) Produce cooling (the process of evaporation produces cooling) which will help keep the air cold enough to support snow 2) This will not offset the surge of warm air advection so if we are seeing strong warm air advection and precipitation is taking a while to reach the ground this leaves a short window for snowfall (especially south of the MA Pike).

Over the next day or so we should be able to fine tune the details on everything.  Based on things right now this is what I am expecting in terms of snowfall across southern New England.  While not likely a major issue, we may have to watch some areas for freezing rain which could yield a glazing.  Below is my map:

 

First Widespread Snowfall of the Season Sunday into Monday?

We have entered a very active weather pattern and this will continue at least through the next week and our next chance for a weather maker comes Sunday night into Monday as our computer forecast models have become in stronger agreement for a storm system to impact southern New England Sunday night into Monday.  This system could also produce the first widespread snowfall of the season, however, we may also have to deal with the transition to sleet, freezing rain, and even rain.  It is still a bit too early to get into further details at this point but we can highlight some of the possibilities and the potential setup.

Embedded in a rather fast/zonal jet stream will be a piece of shortwave energy.  Given how the flow is more zonal/fast this leaves very little room for amplification (the system will not dig and work towards the coast), however, there will be just enough small-scale amplification for the system to strengthen and spawn an area of surface low pressure:

The expected track of this storm is likely to our north and west which typically means either a rainy solution or snow changing over to rain.  However, in this situation we will have a pretty cold airmass in place across the region both at the surface and in the lower-levels of the atmosphere.  With the storm tracking to our north and west this would eventually shift winds in the lower levels of the atmosphere to a more southerly or even southwesterly direction which would usher in warmer air eventually and allow for snow to transition to rain.  Computer forecast models show the system strengthening rather rapidly as it ingests a great deal of moisture from the Atlantic Ocean.  There is a possibility that the system strengthens so rapidly that it actually begins to occlude.  This could lead to a few things; 1) When systems occlude this shuts off the inflow of warm/moist air into the system which is needed for systems to maintain their strength or even intensify.  With this they eventually begin to weaken.  2) The early occlusion would actually prevent the warm front from pushing northward and in this situation that could mean the warm front stays to the south of CT.  This doesn't necessarily mean we don't see warming but the degree of warming could be very weak, especially at the surface.  The surface though is not the only area of concern for warming temperatures but it will be a concern for the lowest several thousand feet of the atmosphere.  With the system strengthening computer forecast models suggest the system could develop closed off low pressure centers at 925mb, 850mb, and 700mb with these lows tracking to our north and west as well.  This would surely advect in a good deal of warmth in the lowest several thousand feet of the atmosphere so even if the surface remained cold enough we would see snow transition to sleet or even freezing rain:

At this point there are still a quite a bit of uncertainties with regards to how the storm evolves, how much snow we see, and when the transition period occurs from snow over to rain and how much sleet or freezing rain we may see.  These are all details which can be ironed out over the weekend.  There are some things, however, which need to be considered with forecasting this system;

1) Very warm ocean temperatures:  Temperatures off the coast are much above-average and this will work to not only enhance the storm but supply a great deal of moisture into the storm.

2) The possibility for an area of high pressure to slide off the coast of Maine:  This would be a HUGE focal point because the flow around the high pressure would establish a more northeasterly flow into our area and that is something that could help keep colder air locked in the surface much longer.  While this wouldn't halt warm air advection aloft, this could allow for a higher likelihood for sleet or even freezing rain so this is something that needs to be watched.

3) Intense lift:  With the surface warm front perhaps stalling off-shore and moisture being thrown up and over the front into the system this could allow for a several-plus hour period of rather heavy precipitation (whether it be snow, sleet, freezing rain, or rain).

Regardless confidence in some major impacts are increasing, especially considering the timing of the storm which could be for the morning rush commute on Monday and perhaps even afternoon commute as well so travel may certainly be impacted.

As we get closer to the event and details become much more clear we can start getting into potential snowfall totals and who exactly changes over from snow and how significant any impacts from sleet or freezing rain may be.

Overnight System

Our active weather pattern continues as yet another disturbance will be moving through our area later tonight.  Fortunately, the timing of this system will be at night and not in the morning like Monday, thus any travel impacts should be quite low.  Like with Monday's system we aren't expecting a major event on our hands as the system is not rather strong.

We are not really looking at one potent shortwave which will be moving through tonight but multiple pieces of shortwave energy moving through a rather fast flow aloft.  With multiple pieces of weak shortwave energy moving through rather than one consolidated piece of shortwave energy this will reduce the degree of large-scale lift and we will see localized areas of stronger lift.  For this reason we will see light precipitation with brief bursts of moderate to heavy precipitation:

 The big question we are dealing with is actually precipitation type.  Does everyone remain all snow?  Does anyone mix?  This is the biggest question with respect to this little system and the reason is due to questions with regards to the thermal profile through the atmospheric column.  The more likely scenario is for mainly a rain/snow mix outside of western CT.  The NAM bufkit for Waterbury, CT and GFS bufkit both show very questionable thermal profiles indicating the more likelihood is for more mixing, again with the exception being western CT where all precipitation should fall mainly as snow and as much as 1-2'' could fall:

The temperature profile will all depend on how much evaporative cooling occurs at the onset of the precipitation.  Currently there is some dry air in place across the state so initially the precipitation will evaporate before reaching the ground.  This process will help to cool the low-levels of the atmosphere.  If enough occurs to cool the column below freezing than more of the state will see snow.  Regardless, this will be a relatively minor system with only a few locations picking up 1-2'' of snow.

Precipitation should begin between 10:00 and midnight and end during the early morning hours tomorrow.  Morning travel should be fine with the exception of maybe a few click spots.

Wintry Commute Monday AM

Prepare for a rather slow commute Monday morning as a quick hitting storm system produces some snow, sleet, and some rain.  While we aren't looking at any big snow totals (outside of the typical NW Hill spots which could get 2-4'') the timing of the snow will make for a rather slow AM commute so expect numerous delays.

Both the NAM/GFS computer forecast models show a piece of shortwave energy moving through southern New England early tomorrow morning accompanied by a decent surge of moisture.  Both models sort of differ with respect to timing and structure of the energy, however, they are in great agreement of track/placement yielding high confidence for tomorrow morning's precipitation mess:

Taking a look at 700mb relative humidity values they are projected to be around 100% tomorrow morning, a strong indication there will be plenty of moisture available and the airmass will be saturated (other levels aren't shown but the surface and lower levels of the atmosphere will be saturated as well):

With plenty of moisture available the next question is with regards to both lift and strength of lifting.  With 500mb shortwave energy moving overhead this will produce a good degree of lift but computer forecast models are also showing a decent surge of lift at the 700mb, 850mb, and 950mb levels.  There will also be some added lift from the nose of a rather strong 500mb jet.  As this strong area of lift moves over the area we will see a period of moderate to perhaps even heavy snow, especially across inland CT.  However, since the system will be a quick mover, the longevity of the snow will be rather brief, thus not much in the way of accumulations.  Across central/southern CT, some warmer air may begin to move in both at the surface and around 2000-3000ft in the atmosphere, with this some areas will see a transition from snow over to sleet and perhaps even rain.  This will also reduce snowfall totals for these locations:

Unfortunately i don't have my pain program so had to use regular paint to make my map but below is what I am thinking for snowfall:

Pattern Change En Route?

For the past few weeks or so long-range computer forecast models had hinted that we would see a major pattern change as early as Thanksgiving and we would see much colder weather work into the Northeastern United States.  This, however, has been pushed off but there are some really strong signals that perhaps around the 8th of December this pattern change occurs but the question is for how long?

The latest 8-10 day 500mb height anomaly forecast from the European model and GFS model continue to suggest that we will see strong ridging develop across northern Canada and Arctic region.  While these models have been showing this in the 8-10 day mean for quite some time the "8-10" day never seems to arrive.  However, there is growing consensus that this will indeed occur and perhaps around December 8th.  Ridging in this area would do one of a few things; it would work to further weaken the polar vortex and also allow to to become displaced further to the south which would enhance the likelihood for much colder Arctic air to sink southward into the United States:

 
The support lies within the forecasts for some of the major global teleconnection indices such as the Eastern Pacific Oscillation (EPO), Arctic Oscillation (AO), and North Atlantic Oscillation (NAO).  One of the major teleconnection patterns, the Pacific-North american (PNA) is not very supportive, however, and with this I do think that the pattern change could be rather brief.  Looking into the major global indices, long-range forecasts suggest that the EPO and NAO will really become negative around December 8th.  When the NAO and EPO are negative this enhances the likelihood for really cold Arctic air to work southward into the United States.  The forecasts for the AO though are much more uncertain (as we will see below).  Given the projected 500mb height pattern featured above the more likely scenario will be for the AO to tank negative as well.  The forecast for the PNA is to also become negative and that actually would enhance potential for a trough out in the western United States which can support ridging here in the east.  If, however, the EPO/NAO are quite negative this would suppress ridging:

So what can we expect?  I think there are some strong signals for at least a brief pattern change around the 8th of December and we will have a period of very cold weather.  The big question is does that mean we will get snow?  That is not so easy to answer, however, if the pattern remains as active as it has been this past week there is a good bet we could have our first big snow threat of the season right around this time.  Hopefully (for snow lovers) we can cash in because this pattern change may be brief and we could return to more a more temperate regime.

Saturday Storm System

The GFS computer forecast model is suggesting a fairly impressive little system working through New England during the day on Saturday.  A vigorous piece of shortwave energy associated with an amplifying trough will potentially yield the possibility for a period of showers and perhaps even some thunder, grauple, and strong wind gusts.  Below are two 500mb charts from today's (November 22nd, 2016) run of the GFS computer forecast model.  The graphic on the left we will focus on the 500mb heights and the graphic on the right we will focus on the vorticity field:

 

With the graphic on the left there is an amplifying (strengthening) trough digging into New England and associated with that is a vigorous piece of shortwave energy which will provide a source for some very intense lift.  As the shortwave approaches, we will also see a fairly decent mid-level jet approach the area as well from the southeast placing us in the right entrance region of a 60 knot mid-level jet streak.  This will also work to enhance lift as the system works through:

Another impressive aspect of this system will be the steepening of the mid-level lapse rates (temperature change with height).  With strong cold air advection occurring in the mid-levels of the atmosphere mid-level lapse rates are forecasted to increase to 6.5 C/KM to 7 C/KM!  In fact, overnight Saturday into Sunday they are forecasted to increase to as much as 8 C/KM!!  That is pretty impressive for this area:

The big question is whether or not we will have enough moisture for the system to work with?  the GFS suggests dewpoints will increase into the mid to perhaps upper 40's which should provide enough moisture for this system to work with.

So what can we expect?  As the shortwave approaches we may see an increased risk for some showers (perhaps heavy at times) and given the presence of steep lapse rates enhancing mid-level instability we can't rule out an isolated thunderstorm as well.  Given cold temperatures around 5,000ft, Some grauple could be possible as well along with some strong wind gusts.

Early Winter Talk...Any Cold On the Horizon?

I'm hoping to be able to sit down and actually put forth a long-range outlook for the upcoming winter, however, due to my schedule that may not be able to happen.  Anyways, when composing long-range forecasts there are a slew of variables and atmospheric/oceanic oscillations that must be looked at.  Some winters (such as last winter when we were dealing with a super strong El Nino) are easier to make a long-range forecast for, however, other winters (in fact probably most) aren't very easy.  This is just due to the fact that many of the oscillations looked at aren't very constant and we don't yet (although our understanding of them is becoming much greater) have a full grasp about how they evolve and what causes them to evolve. 

Anyways, when dealing with this winter and what we can expect here in New England one of the biggest keys which could determine how warm or cold of a winter we have overall and how snowy of a winter we have may very well come down to what happens with this area of low pressure which has become established near the Gulf of Alaska:

If you're hoping for cold and a pattern which favors snow here in New England (especially southern New England) this isn't the best of looks at the 500mb level.  Within the highlighted box we have an area of below-average heights (indicating area of low pressure) and those deep blue colors indicate this is a very strong area of low pressure.  This feature is helping to enhance major ridging across much of the United States (indicated by the red shadings across the country).  This posted image is from today's run of one of our computer forecast models (GFS) for about 5-days out.  What this indicates is we will likely see a period of extreme warmth across much of the country and record highs should fly. 

There is some uncertainties though with what happens to this feature moving forward.  Some computer forecast guidance indicates this area of low pressure will sort of weaken which would reduce the ridging over the United States.  However, at the same time some guidance suggests while this will weaken it will just be replaced by yet another area of low pressure and we would yet again see more ridging develop across the country. 

So what is the significance moving into winter?  While this is NOT a forecast we do have to watch this over the next month.  If this pattern remains constant where we see these deep areas of low pressure remain persistent and strong in and near the Gulf of Alaska, cold shots and snow opportunities may be hard to come by here in New England.  What we want to see is this feature either remain quite weak, retrograde up towards the Bering Sea, or just reverse totally and have high pressure become persistent in this area. 

It is still very early and there are some good signals in place if you're a cold and/or snow lover in New England but we do have work to get there.  Stay Tuned!

Hurricane Matthew: A Threat to Southern New England or Not?

Hurricane Matthew is a VERY dangerous storm wrecking havoc on Haiti and is poised to do the same for much of Cuba as well as the Bahamas.  Turning the attention to us here in southern New England, there has been some talk that Hurricane Matthew will make his way up the east coast and perhaps make a direct landfall somewhere in southern New England.  While there are some computer forecast model guidance which shows this type of scenario the prospects of this likelihood is more unlikely than not.  When forecasting 5-10+ days out one of the key things to recognize and understand is the projected 500mb pattern and how the pattern at this level is set to evolve.  While forecasting in this range can be quite difficult, the 500mb level can give a forecast great clues about what may happen or what some of the more likelihood scenarios are.  Why the 500mb level?  This level is called the "steering" level as the main jet stream at this level typically drives our weather and patterns.  As far as Matthew is concerned, one computer forecast model, the American-run Global Forecast System (GFS) has shown a track into southern New England (some runs have shown a direct hit and some other runs have shown an initial landfall down around the Carolina's before making a second landfall here), there is more to forecasting than just projected sea-level pressure charts.  Despite the track shown on the GFS, the projected pattern on the GFS actually suggests that this sort of track into southern New England is indeed not likely.  We will highlight why below.

We will use the 6z run of the GFS computer forecast model to take a look at the 500mb pattern and how it is projected to shape up over the next several days.  The following images show the projected 500mb heights and normalized height anomalies.  Height anomalies are EXCELLENT to look at because they give you a GREAT clue about well how anomalous a pattern may be.   Not only can you see your ridge and troughs but you can see how "strong" your troughs and rides are.  Below is the initial 500mb height anomalies for 2:00 AM EDT Tuesday morning.  We see a deep trough digging into the western third of the United States, some ridging into eastern Canada, a cut-off low over New England, and Hurricane Matthew right near Haiti/Cuba:

Looking at an animation of how the pattern is projected to evolve over the next 5-days there are several key features to focus on.

1) How the trough in the west evolves as it pushes east across the country
2) Riding that develops off the east coast in the western Atlantic
3) Hurricane Matthew himself

1) West coast trough - Notice how over time that trough goes from digging very deep to sort of lifting and becoming weaker as it pushes through the Plains and towards the Great Lakes region.  Initially, the height anomalies associated with the trough range from -3 standard deviations to -5 standard deviations below average which indicates a trough that is digging very deep.  However, as the days progress these anomalies weaken and this indicates a trough which is much weaker.  What is the significance of this?  Anytime you have a storm system working up the east coast you want a very deep digging trough to be working into the southeastern United States and becoming negatively tilted (we'll touch upon this aspect a bit later) in order for the system to remain close to the coast.  When this occurs the trough captures the system and keeps it locked on the east coast.  If you have a weaker trough which isn't digging or negatively tilted the system doesn't really have any means (although there are some other ways) to hang on the coast and it is more than likely to be kicked out to sea by either the jet stream or the trough.

2) Western Atlantic ridging - Notice how some ridging (indicated by the above-average height anomalies in the red-ish shadings) becomes established just off the east coast in the western Atlantic.  This feature is actually something that will help turn Hurricane Matthew towards the east coast and initially prevent the system from going out to sea.  This actually spells some very bad news for anywhere from FL up to the Virginia's.  This area needs to pay attention to Matthew extremely closely.

3) Hurricane Matthew himself - You can actually see how the establishing ridging helps to steer Matthew towards the southeast coast and then you can see how the weakening trough sort of kicks Matthew out to sea before striking southern New England.

Now what about this "negative" tilt of the trough?  Looking at 6z Saturday morning (2:00 AM EDT) at the 500mb height/vorticity map we see the orientation of this trough as pretty neutral or if anything very slightly negative.  Notice how the height contours (isohytes) dig pretty much nearly north to south..this is what is referred to as a neutral tilted of the trough.  If these dips were oriented more NW to SE this would indicate a more negative tilt of the trough.  Initially as the trough digs through the western United States and into the Plains the trough is negatively tilted, however, as it begins to amplify (or weaken) it becomes more neutral tilted.  When a trough reaches a negative tilt that indicates the system as at maturity and will eventually begin to weaken.  In this case the negative tilt happens very far west:

What about some of the other computer forecast models?  The latest European model is actually pretty similar with the 500mb pattern evolution though there are timing differences with how things go down.  We see a trough which really isn't digging deep into the south and we see a positive tilt to the trough:

  

So what are some of the possible scenarios we can expect up here in southern New England?  While we can't rule out a track into southern New England that scenario is extremely, extremely unlikely due to the reasons stated above.  The more likelihood scenario right now is that Hurricane Matthew takes aim on the southeastern United States and could make landfall anywhere from the east coast of FL up to SC.  From here is where things could diverge.  As that trough works into the east it is possible it captures moisture from Matthew and interacts it with the cold front associated trough and provides much of southern New England with beneficial rainfall.  This scenario would all come down to the timing of everything such as when the trough approaches New England and where Matthew is located...these details can be ironed out a bit later in the week.  It is also possible that after Matthew makes landfall or comes close to the United States coast could just get pushed out to sea all together.  Either way, here in southern New England we should see no significant impacts outside of perhaps some heavy rains (maybe some pockets of flooding depending on how much).

Also, as Matthew works northward, if it were to make a run towards southern New England the likelihood of Matthew weakening substantially would be pretty high.  The forward speed may not be as quick as with a typical tropical system thanks to the building ridge to the east and a slower system moving into slightly cooler waters would weaken it and any interactions with the front/trough would de-characterize its tropical characteristics.

Matthew will continue to garner bit news and attention (and rightfully so due to impacts oh Haiti, Cuba, the Bahamas, and perhaps threat to SE US coast, however, up here in southern New England we should be spared from any significant damage or impacts from a hurricane.

What Can we Expect from Hermine Across southern New England?

The biggest weather story we have been dealing with the past few days is that of what is now Tropical Storm Hermine.  Hermine made landfall as a category one hurricane early Friday morning near St. Marks, FL and is expected to move northeastward along the eastern seaboard.  It is from here we have to watch closely as several computer forecast models have hinted that the system could move far enough northward to provide some impacts across portions of extreme southern New England.

As of 11:00 AM EDT Friday morning we see the 500mb energy associated with Hermine already well inland across southeastern GA.  From here the system is expected to track right up along the eastern seaboard, however, there are some questions with this.  There is still a possibility that the system (or at least the eye...or what's left of it) could move right back over the warm ocean waters off the coast of the Carolina's.  If this does occur there would be a strong possibility that Hermine could actually one again strengthen and keep it's tropical characteristics (remain a warm-core system).  If, however, the system stays centered over land, Hermine will continue to weaken and eventually become extratropical in nature (it will evolve from a warm-core to a cold-core system) and end up becoming baroclonic in nature (meaning it develops warm and cold fronts.  If this happens the system will occlude and that would promote further weakening all well south of southern New England.

As Hermine works up the coast something rather interesting will happen.  There is an area of high pressure that is sliding off to the east across northern New England.  As this area of high pressure pushes off the coast of ME it will act as a "block".  This "block" will do one of two things; 1) it will prevent Hermine from pushing out to sea and 2) It will actually allow for Hermine to stall off the east coast...the big question is where exactly does Hermine stall and this will ultimately determine how significant of an impact we see.

Over the past day or so computer forecast models have become in better agreement that Hermine will stall somewhere either off the Carolina coast or NJ coast.  This scenario would mean for insignificant impacts for extreme portions of southern New England.  We would be looking at periods of heavy downpours and gusty winds.  While not a major issue by any means we could see some minor coastal flooding across the CT shoreline and RI coastline.  This scenario, however, would spell major trouble for the Carolina and especially NJ coastline up to the NYC coast.  With the system potentially stalling and sitting out there for several days we would be looking at significant coastal flooding across these locations and this would be a very bad situation for anyone along the immediate coasts from the Carolina's up to the NYC coast.

What should we expect across CT/RI/SE MA?  In all likelihood, Hermine will occlude too far south to provide much in the way of significant impacts across much of southern New England outside of some gusty winds, periods of heavy downpours, and minor coastal flooding.  Taking a look at some GFS bufkit profiles for New Haven, CT, North Kingstown, RI, and Falmouth, MA during the day on Sunday the GFS is only advertising wind gust potential as much as 35-45 mph and that is more likely along the immediate coast then further inland where gusts could be as high as 30-35 mph.  Much of winds may be do more to the pressure gradient between Hermine and the area of high pressure to our northeast than with Hermine alone.  This is actually something to watch as well because if Hermine is stronger to our south and the high pressure is a bit stronger as well, this would increase the gradient and could allow for some stronger wind gusts...if this occurs we would have to watch for some isolated power outages.

All in all beginning late Saturday we should see an increase in both clouds and humidity levels with a few isolated showers possible.  Overnight Saturday into Sunday the winds should slowly begin to increase as well with the running risk for a heavy downpour.  These conditions will persist through all of Sunday and perhaps lasting into Monday or even Tuesday depending on how long Hermine sits off the coast and where Hermine stalls.  While major to significant impacts across extreme southern New England aren't looking very likely (remember this will be the case from coastal Carolina's up to NYC coast where significant coastal flooding is looking more likely), we will still receive some minor impacts with the periods of heavy downpours, gusty winds, and minor coastal flooding.  If any significant changes to the track, strength, and forecast occur they will be highlighted in any later blog posts.