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Dual Rain Threats This Week, Tropical Storm Gert Intensifying Off the East Coast

Good Evening! 

Today started off decently clear and warm over much of the area, but as the day progressed onward, the elongated area of high pressure just to our south began to move offshore. As it did so, this allowed low level moisture and cloudiness to begin to filter over the region, but still allowed conditions to remain slightly below-average, with highs locked in the upper 70’s to lower 80’s. As of this evening, cloudiness has begun to increase in earnest across the area in response to an impulse of mid level energy working its way north and east along mid level trough. In addition to cloudy skies, this impulse of energy has also sparked some showers over the northern portions of the Mid-Atlantic, with sections of Maryland, Delaware, Pennsylvania, and southern New Jersey all reporting light to moderate showers moving across that area this evening. This area of showers should continue to head east-northeast over the next few hours, but may have trouble making too much northern progress as there is some residual mid level dry air over portions of northern NJ and Long Island. This mid level dry air has also been noted on this evenings radar, as numerous areas of virga (rain not able to reach the ground due to dry conditions) popped up and quickly dissipated soon after.  Overall, conditions should remain cloudy with a chance of a light shower the further south you go, but with increasing moisture, light southerly winds, and increasing clouds at all levels-radiational cooling will be very hard to come except for locations in northern Pennsylvania as well as central New York. This will keep low temperatures in the mild range of the upper 60’s to lower 70’s, with temperatures around 5 degrees cooler to the north and west.

This evenings latest high resolution GEOS 16 visible satellite imagery, regional radar mosaic, surface observations, and WPC frontal locations.

This evenings latest high resolution GEOS 16 visible satellite imagery, regional radar mosaic, surface observations, and WPC frontal locations.

Tuesday Through Friday 

Tuesday morning will likely start off with numerous clouds and possible showers over the region, and another shortwave trough begins to move just to the southwest of the area, bringing another new batch of mid level instability and moisture. At this time, it appears that the best chance for steady rain will be tomorrow morning, likely over the southern portions of the New York Metro area, with locally heavy areas of rainfall possible. As the day progresses, the steadiest rain should begin to head east and off the Mid Atlantic coast. This will likely give way to improving conditions by the mid afternoon hours, with some clearing possible the further away from the coast that you area. With the mid level still feeding moisture in from the south and east, any clearing will likely allow for some instability to build up. Though we will have some instability and weak wind shear to work with tomorrow over the interior, the models indicate an area of sinking air associated with a dissipating mid level system to our north. This should greatly reduce the potential for thunderstorm coverage, but in general isolated shower and thunderstorm development is likely across portions of New York and Pennsylvania tomorrow afternoon and into the evening hours. With the lack of severe parameters coming together, the overall threat for severe weather should be quite low tomorrow, but some stronger storms could produce gusty winds, very heavy rainfall, and even small hail.

As we get closer to New York City, cloud cover and much more stable/sinking air over the region should generally limit and thunderstorm development through the evening hours, and any storms that track close to the area should be on the weakening trend and will likely die-off. With winds coming off of the Atlantic, tomorrow evening will likely be another mild and somewhat-muggy one as lows will likely stay in the low 70’s to upper 60’s across much of the area.

Wednesday should be a much more pleasant day across the Northeast, as dry air behind the mid level disturbance begins to overspread the area, knocking out much of the cloud cover during the early morning hours of the day. Mid to upper level ridging will allow for temperatures on Wednesday afternoon to get quite warm, with highs likely reaching up into the upper 80’s and into the lower 90’s across the region. Few clouds are expected through the evening hours, as a backdoor coldfront pushes from north to south across our area, working to lower dewpoints region-wide.

Thursday looks to be relatively nice for the majority of the day, as the backdoor coldfront halts its progress around the Mid Atlantic region, keep the area warm, but less humid during the day. With dry northwesterly flow established, conditions should be mostly clear across the area. This looks to change later in the evening, as a large mid level system over the Great Lakes looks to approach the Northeast after sunset and into Friday. This system will be accompanied by a strong cold front, which could be responsible for shower and thunderstorm development late Thursday and into Friday, but at this time, it does not appear that this system will carry much of a severe weather threat as well as a flooding threat. This will likely have to be reassessed later in the week, so check back for updates!

This afternoons NAM model showing the progression of Tropical Storm Gert off the east coast, as well as a mid level system over the central part of the county, which may work to bring showers and thunderstorms over our area later this week,

This afternoons NAM model showing the progression of Tropical Storm Gert off the east coast, as well as a mid level system over the central part of the county, which may work to bring showers and thunderstorms over our area later this week

Tropical Storm Gert Nearing Hurricane Intensity 

As of 5pm this evening, Tropical Storm Gert was located roughly 450 miles to the west-southwest of Bermuda, and moving north at around 8 miles per hour. Gert has taken advantage of a relatively favorable environment today characterized by low vertical wind shear, very warm sea surface temperatures, moist air, and slow storm motion. This allowed the storm to develop intense thunderstorms near the core of the system, which in turn began a period of intensification to just below hurricane status-at 70 mph. Recent visible satellite images from the GOES-16 satellite showed that the cloud tops of Gert were warming a little, maybe indicating a brief halt in the intensification process, but with the storm located over very warm water and under a favorable environment, it appears quite likely that Gert will become a hurricane within the next 12-18 hours.

Gert will continue to track to the north as it rounds the western edge of the Bermuda high tomorrow, likely continuing to strengthen as it does so. Gert will likely begin to accelerate and take on more of an easterly component later tomorrow, as a shortwave trough moves over the Northeast. As the storm begins to interact with the shortwave trough over the northern Atlantic ocean, it will likely begin its extra-tropical transition by late Wednesday. Thereafter, the storm is likely to remain a powerful extra-tropical system, which may eventually threaten portions of Europe further down the line. Impacts for the east coast will be limited to increased wave swells and a high risk of rip currents. The main risk from Gert will be help by any maritime craft venturing off the east coast this week.  Elsewhere in the Atlantic, there is an area of disturbed weather located in the far eastern Atlantic which may try to gradually develop into a tropical cyclone over the next few days as it heads generally WNW at 15mph.

GOES-16 visible satellite imagery of Tropical Storm Gert off of the southeastern coast of the US this evening (Courtesy of simuawips.com)

GOES-16 visible satellite imagery of Tropical Storm Gert off of the southeastern coast of the US this evening (Courtesy of simuawips.com)

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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)

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Steve Copertino

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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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Steve Copertino & Doug Simonian 

 

Tuesday afternoon's 3km NAM model showing clusters of thunderstorms in New Jersey on Wednesday afternoon (Tropical Tidbits).

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.

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