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Severe Thunderstorms and Heavy Rain Inbound, Eclipse Details for Monday!

Good Evening! 

As promised earlier in the week, today was looking like it was going to be the most active day in the forecast period, and it certainly did not disappoint! The large upper level trough and associated surface low pressure system located over the Great Lakes region pushed a warm front through most of the New York metro area and Northeastern states early this morning, which brought very heavy rainfall, lightning, and locally gusty winds. While the rain was quite heavy in some locations, widespread flooding was not an issue, and any flooding was confined to street and small stream activity. As this warm front moved through the region, it ushered in a very moist and unstable airmass characterized by 3000-4000j/kg^2 of convective available potential energy (CAPE) and very, very moist precipitable water values-above two inches in some locations. The main question was whether or not the low level jet associated with the sprawling low pressure system would be strong enough to wipe out some of the cloud cover of the region and allow for further destabilization and dynamics to take over, but as we saw early this afternoon, the sun did in fact make an appearence over eastern portions of the Northeast. As the sun heated the soaked grounds from this mornings storms, this created and even more unstable and moist airmass for any future storms to work with.

Later in the afternoon-around 4pm or so, discrete thunderstorms began to form over portions of Pennsylvania and the northern Mid Atlantic states in response to moderate to strong mid level forcing interacting with the very unstable environment present. Rapid growth into supercell structures occured in the strongest of storms, which went on to produce severe hail, damaging winds, and very heavy rains which caused flash flooding. Eventually the large scale forcing took over a good portion of the unstable warm sector and this led to the development of numerous showers and thunderstorms, which congealed into a more linear line of storms. As of 5pm, this line was located over portions of Pennsylvania and Maryland. While the line has lost some strength in the past hours, there are a few areas of stronger activity that are currently severe warned for damaging winds and potentially severe hail. With wind shear being in the moderate 25-45 knot range and cloud levels being quite low, these embedded stronger cells may pose a brief tornado threat as they head east into New Jersey within the next few hours.

This afternoons NAM model showing very high PWATS in addition to strong mid level winds, perfect for the development of heavy rain across the area this evening.

Otherwise, this line looks to propagate east at a gradual pace, with the main threats outside of the severe activity being torrential rainfall which can produce flash flooding within a matter of minutes. This threat has been exacerbated due to this mornings storms leaving behind very moist soil which may have trouble if rain rates do reach the 1-3″ range. As these storms head east this evening, they will begin to encounter a much more stable airmass from the Atlantic ocean, which should gradually shut down any strong to severe thunderstorm activity that may remain close to sunset. The heavy rain threat will still exist until these storms and the accompanying cold front push out past the region and into the open waters of the Atlantic.

For the severe risk this evening, the Storm Prediction Center in Norman, OK has issued a severe thunderstorm watch for the majority of the Northeast and Mid Atlantic States. The main threats include strong wind gusts up to 70 mph, locally severe hail up to ping-pong ball size, torrential rains, and frequent lightning.

In addition, the National Weather Service in co-ordinance with the Weather Predictions Center in Camp Springs Maryland has issued a Flash Flood Watch for rainfall rates of around 1-3″/hr possibly producing small stream and urban flooding. Rainfall totals may be in the 3-6″ range where the heaviest storms track over this evening.

This evenings latest high resolution Goes 16 visible Satellite imagery, regional radar mosaic, surface observations, and severe warning from the NWS (Courtesy of Simuawips.com)

This evenings latest high resolution Goes 16 visible Satellite imagery, regional radar mosaic, surface observations, and severe warning from the NWS (Courtesy of Simuawips.com)

Saturday and Sunday 

Conditions look to gradually improve beginning tomorrow morning as an are of high pressure begins to build off to our north and west. This will allow for decreasing cloud cover, warmer temperatures, and light and variable winds throughout much of the day. Expect highs to generally be in the mid to upper 80’s, with lows dropping down into the low to middle 60’s overnight. Conditions will likely be quite the same on Sunday as well, as the area of high pressure begins to move overtop the region. Conditions this weekend should be rather favorable for any outdoor activities, but we may have to keep an eye on the beaches as there may be at least a moderate risk for rip-currents and strong wave action along the coasts.

Mondays Eclipse Weather 

With the models coming into their more-reliable range as of this afternoon, things still look quite favorable for the viewing of the partial eclipse on Monday afternoon. The area of high pressure that will be approaching the region this weekend looks to be just offshore of the NJ coast by mid-Monday afternoon, which should allow for onshore flow to overspread the area. This will create a rather stable airmass, with few prospects for cloud development.  To look at it another way if you do not trust a few models, the European ensembles, which consists of 50 different model runs and one control run, show less than ten-percent cloud cover for NYC during the event-which is near perfect! All in all, conditions look excellent on Monday for experiencing quite a rare event, but remember to do so safely with the special eclipse glasses that can be found online and at local stores.

ECMWF Ensembles showing a blend of 51 models with less than a 10% chance of cloud-cover for the eclipse on Monday!

ECMWF Ensembles showing a blend of 51 models with less than a 10% chance of cloud-cover for the eclipse on Monday!

For more information and posts like this one, make sure you sign up for Premium Forecasts — where multiple detailed articles, videos, and interactives are posted each day. Also, come interact with our staff and many other weather enthusiasts at 33andrain.com!

Have a great evening!

Steve Copertino

 

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Severe Weather Possible This Afternoon, Yet Another Unstable Pattern Next Week

Good Afternoon! 

Despite some heavy showers and thunderstorms that moved through the immediate New York metro area this morning, most of the area was able to clear out quite significantly this afternoon. With high humidity in place and full sunshine, we saw the development of numerous cumulus clouds, especially to the north and west of the city. With instability rising gradually through the early afternoon hours, shear kicking in, and forcing from an approaching upper level trough all coming together, we have seen numerous showers and thunderstorms go up over portions of the Mid Atlantic and Northeast regions. Given rather unimpressive lapse rates, unidirectional shear vectors, and a general broad area of forcing, this activity has mainly been limited to multi-cellular and pulse-cell storms. These storms will mainly be capable of damaging winds and possibly a wet micro burst or two, as the weak mid level lapse rates will fail to sustain any significant updrafts over much of the region. As these updrafts collapse over time, they may do so rather quickly, leading to winds up to 60 mph and torrential downpours, which may cause localized flooding.

However, as we head deeper into western Pennsylvania and New York state, the vertical wind shear profile becomes a little more favorable for more organized convection, and we have seen some embedded supercell structures form within larger convective masses. These storms will have a much higher threat of damaging winds, large hail, and even a brief tornado or two. This stronger activity will likely remain exclusive to this region, as the severe parameters quickly become less supportive for anything too strong the further east you head.

Regardless, the rest of the afternoon should remain quite nice for a typical August day, with highs deep into the 80’s-possibly getting to that 90 degree mark in some locations. As we mentioned before, humidity will be increasing ahead of the front located off to our east, so it will feel quite muggy out, and any locations that saw some of the heaviest rains this morning will have the added moisture in the air from evapotranspiration.

As we head into the evening hours, we should see the development of more showers and thunderstorms over the Northeast, as the previous cells begin to collapse and leave convergent boundaries as to which new thunderstorms can form along. Winds from the south will continue to pump moisture/instability into the area, with CAPE values remaining in the 1200-2800j/kg^2 range until sunset. In addition to the instability in place, a very weak warm front will be passing through the region, and this may work to locally improve wind fields, but only to a small extent. At this time, it appears that the best chance for showers and thunderstorms this evening will be over portions of southern New York, eastern Pennsylvania, and possibly far northwest New Jersey. These showers and thunderstorms should mainly be capable of producing gusty winds and small hail, with heavy rain likely as well.

This afternoons latest regional radar mosaic, high resolution visible satellite imagery, surface observations, and severe warnings. Courtesy of Simuawips)

This afternoons latest regional radar mosaic, high resolution visible satellite imagery, surface observations, and severe warnings. Courtesy of Simuawips)

Saturday and Sunday 

Saturday may start off cloudy and with a few showers and an isolated thunderstorm in spots as the large upper level trough to our west finally begins to move through. This shower and thunderstorm activity should move rather quickly through the northern portions of the metro area, but brief heavy rain, gusty winds, and small hail may all be possible with any stronger areas of activity.

Afterwards, a cold front associated with the large upper level trough will finally move through the Northeast during the afternoon hours, and will likely clear any residual showers out. Behind this front will be some refreshing Canadian air that will also be packing much lower humidity with it as well, so there should be a noticeable change in airmasses by lunchtime tomorrow. With clearing skies, low humidity, and light westerly winds behind the front, highs should be able to get into the low to middle 80s tomorrow, which is right around normal for this time of year. Tomorrow evening will be a very pleasant one, as the skies begin to clear out and winds out of the north and west continue to usher in cooler air. Conditions will be in place for radiational cooling to take place over the entire Northeast, which is somewhat uncommon for this time of year. This will allow for lows to fall into the upper 50’s to low 60’s across our area-with some locations to the far north and west possibly seeing low 50’s tomorrow evening!

Sunday looks to be the “gem” in this forecast period as light winds, low humidity, and warm temperatures in the 80’s will dominate the day region-wide. Clouds may begin to increase later in the evening, but overall Sunday should be an excellent day for any outdoor activities!

CLICK TO ANIMATE This afternoons RPM model showing the evolution of this evenings storms, as well as the cold front passage tomorrow morning/afternoon (courtesy of WSI)

CLICK TO ANIMATE
This afternoons RPM model showing the evolution of this evenings storms, as well as the cold front passage tomorrow morning/afternoon (courtesy of WSI)

Next Week

Our eyes will once again shift to the west, as yet another northern stream disturbance begins to approach our area. As this system approaches, it will begin to dig up a serious amount of warm air and moisture from the south and west and direct it towards the Mid Atlantic and Northeastern states. As the mid to upper level system draws closer, a frontal boundary will likely set up. Below this boundary there will be very warm and muggy conditions, while locations to the north experience more seasonable conditions. Above the surface, a large and very impressive upper level jet streak will be nosing in, which is a tell-tale indicator of potential heavy rain for this area. the questions that remain to be answered at this time are where does this frontal boundary set up, how much instability will be in place, and will these ingredients come together at the right time to produce widespread heavy rain? If these conditions do come together on Monday in the correct manner, then we may have to watch for potential flooding rains and much cooler temperatures to start off the week. We will likely have to revisit this system as more data becomes available.

This system should exit the coast late Monday, and an area of high pressure should begin to take over for Tuesday and into Wednesday. However, we may have another rain chance later in the week as the active northern stream regime shows up once more.

This afternoons GFS model showing the very favorable juxtaposition of an expansive upper level jet streak that could potentially aide in the development of heavy rain on Monday (courtesy of Simuawips)

This afternoons GFS model showing the very favorable juxtaposition of an expansive upper level jet streak that could potentially aide in the development of heavy rain on Monday (courtesy of Simuawips)

For more information and posts like this one, make sure you sign up for Premium Forecasts — where multiple detailed articles, videos, and interactives are posted each day. Also, come interact with our staff and many other weather enthusiasts at 33andrain.com!

Have a great evening!

Steve Copertino

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Mesoscale Update: Severe storms, heavy rain likely today

Click this link/article for the Latest Video Analysis  from 2:40pm EDT!

 

A warm and humid airmass has settled into the region this morning, ahead of a large mid level atmospheric trough digging through Southeast Canada and into parts of the Northeast States. With a surface low well to the northwest of the area, a cold frontal boundary will shift eastwards through Pennsylvania and New York later today, providing lift and forcing for widespread thunderstorms to develop.

These thunderstorms are likely to be fueled by a very warm and humid airmass which is already in place this morning. A deep southwesterly flow has become established throughout the region, leading to dew points in the upper 60’s and lower 70’s throughout the Northeast states. Temperatures this afternoon will rise into the 80’s, further enhancing the instability in the atmosphere.

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Midday Zones Update: Heavy Rainfall and Severe T-Storm Threat This Afternoon

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