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.