PM Rain Exits, Storms and Cooler Weather Possible This Weekend!

Good Evening!

After a relatively hot and humid day across the entire Northeast and Mid Atlantic regions, we have seen large-scale thunderstorm development courtesy of the mid level shortwave that we discussed back on Monday. This shortwave was located to the west of the area, and with CAPE values of around 2000-3000 j/kg^2, PWATS near 1.5″, and strong low level lapse rates, the weak amount of energy associated with the disturbance was more than enough to set off numerous showers and thunderstorms around 2pm. Due to a significant lack of vertical wind shear, these storms were not able to move all that much from where the initial updrafts formed, and thus most cells rained themselves out over time. However, when these updrafts collapsed and the rain cooled air rapidly sunk to the surface, it created new boundaries which served to provide breeding grounds for renewed storm development. In some locations we saw this happen three to even four times over, which caused serious street flooding.

In addition to the street flooding, cool/dry air aloft allowed for some of the more robust thunderstorms to develop marginal to severe hail stones, with some reports of stones reaching the 1.75″ mark! Some folks may have noticed that these storms were also producing a cooler rain than one would expect during August, and this also can be attributed to the cooler air aloft. These drops were whats know as “Big Drops” (I know, very creative) and form when an updraft just isn’t able to keep ice suspended long enough to freeze sufficiently to reach the ground as hail. However, a few thousand feet up in the atmosphere, these drops were frozen, and when they crashed into one another, they create a negatively charged particle in the atmosphere, called an electron. When enough of these electrons build up in an updraft, they connect with positively charged particles (protons) at the surface, the path they take to get to one another creates lightning! With a ton of ice in the atmosphere from numerous updrafts this afternoon, there was a very impressive amount of lightning that went up across the area. Some of this lightning even caused damage to houses and property, with some areas losing power. Otherwise, today’s storms mainly posed a very heavy rain, lightning, and gusty wind threat.

As of six o’clock this evening, most of the showers and thunderstorms that formed early this afternoon were finally beginning to wind down. Lightning activity over the area has greatly weakened over the past hour or so, and this also points towards a gradual dissipation of the rest of the thunderstorm activity. As this time, we think that the heaviest showers and thunderstorms should dissipate by sundown, with only a few lonely cells remaining thereafter. Some residual cloud cover is likely as we head into the overnight hours, and this will help to keep overnight lows rather mild, with temperatures dropping to around the low to middle 60’s.

This evenings latest regional radar. high resolution visible satellite, surface observations. and severe warnings, showing the bulk of the heavy rain dying off. This trend should continue as we head deeper into the evening (Courtesy of Simuawips)

This evenings latest regional radar. high resolution visible satellite, surface observations. and severe warnings, showing the bulk of the heavy rain dying off. This trend should continue as we head deeper into the evening (Courtesy of Simuawips)

Thursday and Beyond

Thursday should start off just as the past few days have, with any low clouds quickly burning off by the mid to late afternoon hours. This will allow afternoon temperatures to climb significantly during the afternoon hours, with highs likely reaching the middle 80’s to lower 90’s across the area. With a moist airmass in place tomorrow, we should see the region destabilize once again by the mid to late afternoon hours, similar to as we saw today. The main difference will be that tomorrow does not look to have a coherent area of forcing to initiate thunderstorm development, so any thunderstorms tomorrow afternoon will likely have to rely on convergent boundaries from local sea breezes. This activity will likely be limited to a heavy rain and lightning threat given the lack of favorable parameters for anything outside of heavy thunderstorms. Storms should gradually fade tomorrow evening, leaving generally mild and humid conditions in their wake.

As we head into the first half of the weekend, a large shortwave trough diving out of Canada will provide a threat of heavy rain and possibly some thunderstorms over the area as moisture begins to surge north from the Gulf States. This system will be watched closely, as it does have a very favorable upper level jet streak which could potentially enhance a heavy rainfall threat over our area. A strong cold front looks to push through late Saturday and into Sunday, which should bring not only cooler temperatures to our area, but also much lower humidity compared to what we’ve been seeing-which should make for an enjoyable end to the weekend!

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Have a great evening!

Steve Copertino & Doug Simonian 

 

Premium Long Range: Cooler, Active Pattern Next Week…More Changes Late Month?

Good morning! More summer-like weather with more heat and humidity will continue for the rest of the week,with some scattered showers and thunderstorms possible each afternoon or evening. But it appears the Western Hemispheric pattern will undergo another more significant changes to support some cooler weather again for next week.

First changes, will start occurring over North Pacific as usual this week. An upper-level low will be near the Aleutian Islands or Southwest Alaska. This will cause a high-amplitude ridge to build over the West Coast by early next week. This will result in a larger trough digging and encompassing much of the Central and Eastern US over for next week.  Then cooler airmasses from Canada will be invading the CONUS, with temperatures well below over the much of the Northern and Central Plains and into parts of Great Lakes and Ohio Valley.

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Locally Strong Thunderstorms Possible on Wednesday

Good evening! We hope you enjoyed this summery Tuesday. This article is going to just focus on the potential for thunderstorms on Wednesday afternoon — some of which could briefly pulse to strong to even severe status.

It all starts with a shortwave trough that will be moving into the area on Wednesday, bringing plenty of vorticity with it and thus lift. This is a true lifting mechanism that we have not had over the past couple of days, which should allow coverage of thunderstorms to be higher on Wednesday than on Monday and Tuesday.

Tuesday afternoon's NAM model valid for Tuesday afternoon shows a shortwave trough with embedded vorticity helping to trigger some showers and thunderstorms in New Jersey.

Tuesday afternoon’s NAM model valid for Tuesday afternoon shows a shortwave trough with embedded vorticity helping to trigger some showers and thunderstorms in New Jersey.

In the midst of this warm and humid airmass, surface-based instability should be pretty high already, but the fact that this shortwave trough will be lowering heights a bit but also not contaminating the airmass with too much moisture will help increase lapse rates somewhat significantly. This allows for updrafts to potentially be more robust and for more of the cumulonimbus cloud to be in dense, cold air aloft — both factors allow for more hail formation, the potential for downburst gusty winds, and somewhat vivid lightning.

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Premium AM Update: More Heat & Humidity Today…PM T-Storms Possible Wednesday

Good morning! More typical summer-time heat and humidity is in store for next few days. For today, weak high pressure and upper-level ridging will be over Northeast and Mid-Atlantic region,. This will result in mostly sunny skies for much of the day. Latest models show 850mb temperatures between around 15° C to 17° C with very light westerly winds later today. This will support high temperatures in the upper 80s to around 90 over much of the local region today. A weak flow will allow for some sea-breezes to develop again this afternoon and keep temperatures from rising out lower to middle 80s right along the shores.

There isn’t much of a trigger for convection today. But a surface trough will develop again over  the Interior. The NAM model forecasts instability to build with MLCAPE 500 -1000 joules. So few isolated showers and thunderstorms could develop this afternoon over Interior parts of NY, PA, New England and over Northwest NJ. The main threat from thunderstorms with a very weak shear and poor mid-level lapse rates, with be locally heavy rainfall, as any thunderstorms will likely be slow-moving. Therefore these showers or thunderstorms are not likely make it down to more coastal areas, before diminishing closer to sunset.

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