Posts

Steven Copertino

Public Analysis: Third Heatwave of the Year Possible, Increasing Thunderstorm Threats This Weekend

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Good Evening! 

Today has been another day in this string of hot and muggy weather. This semi-tropical airmass can be attributed to a large area of high pressure over the western Atlantic, which is in a perfect position to pump the uncomfortable dewpoints and heat northward. This airmass is likely to remain in place through the weekend and possibly even into the first half of next week, before a cold front associated with a strong disturbance originating from the Pacific Ocean sweeps through.

Regardless, after some low level clouds and patchy fog that built up during the early morning hours burnt off, temperatures were able to quickly rise into the upper 80’s and lower 90’s-with some locations reaching the middle 90’s! As stated earlier, the high pressure out in the western Atlantic has been pumping in very impressive dewpoints over the region. Dewpoints will range in the 65-75 degree area, which is right around the “uncomfortable” and “oppressive” tiers of the spectrum for this area. When you take temperatures in the upper 80’s to middle 90’s and factor in these very high dewpoints, the apparent temperature-or how hot it feels rises quite a bit. Due to this, the National Weather Service has issued a Heat Advisory, which will likely last until Thursday evening. Day time highs in the low 90s combined dew point temps around 70 will produce heat index values in the upper 90s across the advisory area, which is forecast to continue through Thursday. “The heat and humidity may cause heat stress during outdoor exertion or extended exposure. Extreme heat can cause illness and death among the at-risk population who can not stay cool.”

Additionally, all of this low level moisture will allow for instability to rise over the area as well. Some showers and thunderstorms are currently going up over central and eastern Pennsylvania. These storms formed as a result of some residual energy from a dying upper level low interacting with the warm/unstable airmass over the region. Thankfully, the trigger energy from this disturbance is not all that strong or organized, so widespread thunderstorm development does not seem likely over the area. However, any showers and thunderstorms that do develop may have very heavy rainfall associated with them as the atmosphere is loaded with precipitable water.

The hot and humid conditions will last well into the evening hours, likely until sunset, and even then temperatures will be well-above normal tonight as the muggy airmass keeps the entire area locked into the low to middle 70’s for overnight lows.

This evenings latest high resolution satellite imagery, regional radar mosaic, and surface observations,showing a very warm and humid day across the area with some scattered shower and thunderstorm activity to our west (Courtesy of Simuawips.com)

This evenings latest high resolution satellite imagery, regional radar mosaic, and surface observations,showing a very warm and humid day across the area with some scattered shower and thunderstorm activity to our west (Courtesy of Simuawips.com)

Thursday into Friday 

Thursday will likely start off quite clear, which should allow temperatures to skyrocket during the early afternoon hours.  Light west/southwest winds will also be ushering in another round over very high dewpoints, and with slightly higher mid level temperatures, we expect highs tomorrow to be slightly higher than they were this afternoon, with much of the area in the upper 80’s to middle 90’s. This combination will make apparent temperatures (Real Feel) rise into upper 90’s and even lower 100’s across the area. This heat and humidity combo can be dangerous to some people, so make sure to stay hydrated and do not overexert yourself.  Weak seabreeze fronts may develop along the shores of Connecticut, Long Island, and New Jersey, and this could help to knock the temperatures and humidity down a few degrees as the afternoon marches onward.

Instability will once again build over the region, and with an active quasi-zonal flow being established over the region, we may have to worry about a complex of showers and thunderstorms moving through the area late tomorrow afternoon and into the evening. Precipitable water values will still be quite high and there will be some weak shear present, so any showers and thunderstorms that develop will have a risk of torrential downpours that can potentially cause flash flooding, as well as some locally damaging winds.

Friday looks to be another very hot and humid day with clear skies and increased low level moisture. It is looking quite possible that if Thursday and Friday both produce highs in the 90’s, then numerous stations will record their third “heatwave” of the year. It is also quite possible that the Heat Advisory for the area gets extended until Friday evening, as dewpoints and temperatures will still be high enough to make conditions seriously oppressive.

This evenings latest Rapid Precision Model, showing the potential for gusty showers and thunderstorms moving through the area by late Thursday afternoon/evening. Some of the stronger storms may be able to produce flash flooding and locally damaging winds. (Courtesy of WSI)

This evenings latest Rapid Precision Model, showing the potential for gusty showers and thunderstorms moving through the area by late Thursday afternoon/evening. Some of the stronger storms may be able to produce flash flooding and locally damaging winds. (Courtesy of WSI)

This Weekends Severe Thunderstorm Threat

As we mentioned before, the Northeast will be within a west to east “zonal flow” this weekend, which will have numerous short wave trough embedded withing the flow. This looks to change on Sunday, when a large Pacific disturbance (that is currently off the West coast) gets caught in the flow and is located just to our northwest. The massive area of high pressure to our east over the Atlantic will still be supplying very moist and unstable air directly into the area while yet another area of high pressure over the central part of the country advects what is known as an Elevated Mixing Layer (or EML for short). This EML is very favorable for thunderstorm development, especially severe thunderstorm development. With the shortwave to the northwest in Canada providing upper level support and shear, the very moist and unstable airmass being pumped in from the south, and the support from the EML, it seems quite possible that widespread thunderstorm development will be possible on Sunday, with a higher than average chance that at least some of the storms become severe over a good portion of the Northeast/Mid Atlantic.

The main questions right now appears to be just how much influence will the previous nights possible convection last into the day on Sunday, and how far north will the surface low develop to our west. If we can get a strong enough surface low to develop over the eastern Great Lakes region with increased instability, then we may have to watch for the development of quite a few severe thunderstorms capable of wet microbursts, large hail, and flash flooding. We will have an update later this week to go over this potential threat once again.

This afternoons European model showing modest amounts of instability, decent wind shear, along with good timing for the possible development of strong to severe thunderstorms over the Northeast on Sunday

This afternoons European model showing modest amounts of instability, decent wind shear, along with good timing for the possible development of strong to severe thunderstorms over the Northeast on Sunday

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Have a great evening!

Steve Copertino

Steven Copertino

Public Analysis: Improving Conditions This Evening, Excellent Weekend Ahead!

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Good Evening! 

Today we saw the development of numerous showers and thunderstorms across the southern half of the metro area, with some of the storms being on the strong to severe side. These storms were fueled by the remnant frontal boundary that sank southward to portions of southern NJ earlier this morning. Deep tropical moisture was able to remain anchored within this boundary, and as daytime heating took over, instability was able to increase quite markedly over portions of southern Pennsylvania and New Jersey. As the last in the long series of mid level disturbances embedded in the west to east flow approached this very moist and unstable airmass, thunderstorms rapidly developed-bringing large hail, damaging winds, and very heavy rainfall. Some localized reports of wind damage were reported in Pennsylvania, Delaware, and portions of New Jersey, but overall it wasn’t a huge day for severe weather.

The showers and thunderstorms gradually moved into a more stable marine airmass near the coast, which caused them to weaken below severe thresholds and limited impacts to mainly heavy rain and frequent lightning. These showers will continue to head off the coast later this evening, giving way to more mild and cloudy conditions. As we head deeper into the evening, a shortwave trough and the accompanying energy will begin to push into the region, and due to the fact that there is still some residual moisture/instability, we cannot rule out a couple showers and even a late thunderstorm developing. Any storms that form would almost certainly remain below severe limits, with the main threats just being heavy rain and gusty winds.

Lows this evening will remain right around what the current temperatures are due to thick cloud cover and residual low level moisture trapped due to a temperature inversion a few thousand feet up in the atmosphere. Some patchy fog may try to develop this evening for some locations, but overall development should not be all that widespread.

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This evenings latest regional radar mosaic, surface observations, and high resolution visible satellite imagery, showing the bulk of the showers and thunderstorms moving off the Mid Atlantic coast (Courtesy of Simuawips)

This Weekend

Improving conditions are expected starting on Saturday as the upper level trough that has been providing the area with numerous rain chances finally swings through early in the morning hours. This will cause any residual fog to quickly dissipate as the low level moisture is quickly swept out of the region. Clouds should also begin to decrease in earnest as an area of high pressure begins to gradually build in from the west, centered over the Ohio Valley. Conditions tomorrow should feel much improved from the past few days, with dewpoints dropping quite considerably, giving way to a much more comfortable airmass. With increasing sunshine, a warm mid level airmass, and low moisture content in the atmosphere, temperatures should be able to rise to around seasonable levels-with lower to middle 80’s likely areawide.

High pressure will continue to build over the area as we head into the evening hours, allowing for even clearer conditions to develop just in time for sunset. The high pressure will also allow winds to become quite calm by the early evening hours, and with calm winds, low dewpoints, and clear skies, its looking quite likely that some radiational cooling will take place tomorrow evening, which should allow temperatures to drop into the middle 60’s across the entire area, which is just around normal for this time of year.

Sunday will likely be repeat of Saturday, with clear skies, low dewpoints, and light winds being the theme once again. The mid level airmass will be a little warmer on Sunday due to winds shifting to the west/southwest, so we expect highs on Sunday to be a little warmer, with temps reaching into the upper 80’s and lower 90’s across the region. Sunday evening will also be near-perfect, with clear skies and light winds, which will allow for cooler temperatures to return. Overall, it’s looking likely that this weekend will be quite beautiful and should be great for any outdoor activities as we undergo a temporary airmass change!

This afternoons high resolution North American Model, showing light northwesterly winds, warm temperatures, and an overall pleasant airmass over the area, which should make for a beautiful day!

This afternoons high resolution North American Model, showing light northwesterly winds, warm temperatures, and an overall pleasant airmass over the area, which should make for a beautiful day!

Next Week

The next threat of rain looks to come early in the week next week, as an upper level trough approaches from the west and drags another humid airmass from the south. This will greatly increase instability over our area, which will set the stage for afternoon thunderstorms, capable of heavy rain and gusty winds. This afternoons model guidance disagrees with regards to the handling of this piece of energy as it heads towards our area, but it seems possible that the threat of showers and thunderstorms stays around until at least Tuesday. Temperatures for the beginning half of the week should be around-normal, but this will be highly dependent on the amount of cloud cover and rainfall that we may receive.

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Have a great evening!

Steve Copertino

Steven Copertino

Public Analysis: Oppressive Heat and Humidity, Strong Thunderstorm Threat Thursday and Friday

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Good Evening! 

As we stated earlier this week, conditions were once again going to become unstable as a deep tropical airmass works its way over the region over the next few days. This was quite noticeable today as dew points rose into the uncomfortable (66-70) and oppressive (71-75) degree ranges! Coupled with highs in the mid to upper 80’s, heat indices were able to climb into the middle 90’s in some locations, promoting the issuance of a Heat Advisory for counties in Pennsylvania, New Jersey, and New York-for now. A Heat Advisory is issued when the combination of heat and humidity is expected to make it feel like it is 95 to 99 degrees for two or more consecutive days, or 100 to 104 degrees for any length of time.-NWS 

With this increased instability and plentiful moisture trapped in the atmosphere, all we needed today was a little daytime heating to really destabilize the atmosphere. The first in a series of quick-moving shortwaves in a general west to east flow was today’s trigger mechanism that set off numerous strong to severe thunderstorms over portions of southern New England, and even portions of Connecticut. These storms were mainly very heavy rain producers as the atmosphere did not have enough energy in place to keep the significant amount of moisture lofted within the low to mid levels of the atmosphere. As the updrafts that held all of this moisture began to collapse, they created very high rain rates, with some nearing close to 2″/hr! As the more robust updrafts quickly collapsed  and the rain cooled air rushed to the ground, this created localized instances of wet microbursts, which were the cause of some tree damage in Connecticut.

As the forcing mechanism for this afternoon convective outbreak begins to quickly move off to our east, showers and thunderstorms should gradually sink further south and east with time. As they do so, they will also encounter a slightly less favorable environment needed to sustain themselves, however it would not be out of the realm of possibilities that a few more short-lived cells go up near sunset, capable of small hail, heavy downpours, and occasional lightning.

The rest of the evening will likely remain quite muggy, as the tropical-like airmass remains locked in place due to rather stout low level winds from the west/southwest. Lows this evening will be lucky to get down into the lower 70’s, so expect a rather muggy night ahead with a slight chance of some showers in the very early morning hours.

This evenings latest regional radar mosaic, regional surface observations, and high resolution visible satellite imagery, showing left-over showers and thunderstorms over the area gradually moving to the east/southeast (Courtesy of Simuawips.com)

This evenings latest regional radar mosaic, regional surface observations, and high resolution visible satellite imagery, showing left-over showers and thunderstorms over the area gradually moving to the east/southeast (Courtesy of Simuawips.com)

Thursday Into Friday 

Thursday is likely to start off with a few broken or scattered clouds, with some “hazy” conditions likely as well. As the daytime heating gets off to a rather quick start tomorrow morning, temperatures will quickly shoot into the upper 80’s to lower 90’s once again, and when factoring in the very high dewpoints, conditions will become quite miserable in some locations. Heat indices may swell into the upper 90’s and even into the lower 100’s during the peak heating hours of the afternoon! As another in a series of mid level disturbances rushes over from the Great Lakes region, mid level shear ahead of this wave will begin to increase in earnest, creating a conducive initial environment for afternoon thunderstorms to fire in over the area.

While the initial setup of parameters over the area will be primed and ready for thunderstorm development by the afternoon, the main question is regarding the timing and location of the mid level disturbance that would be able to trigger thunderstorm development. What may wind up happening is that the initial thunderstorms may fire over portions of southern New England (like they have many times this year before) and then begin to sag southward along a frontal boundary to our north. The problem with this is that by the time that the showers and thunderstorms begin to propagate to the south, the best parameters over our area will begin to fade. This would mean that as any storms move south, they would gradually weaken with time, which would mitigate the overall severe threat. Regardless, the setup tomorrow looks to support at least torrential downpours, frequent lightning, gusty winds-with the potential for more damaging wind gusts and hail in the strongest cells.

This afternoons RPM model showing the progression of the frontal boundary tomorrow morning and through the afternoon hours (Courtesy of WSI)

On Friday, a broad area of low pressure will begin to stretch over into our area, likely starting the day off with rather thick cloud cover and cooler temperatures. Though the model diverge on this quite significantly, there does appear to be a rather good chance that a frontal boundary will be stalled somewhere along the Metro area, or just to our north-which will dictate much of Friday’s weather. This stalled frontal boundary will act as a near-perfect source for lift, as deep low-level flow ushers in PWATS of around 2.25″-2.5″. Additionally, CAPE will also become quite plentiful due to this tropical airmass, and this instability will be met with increasing low to mid-level shear from the stalled frontal boundary. Due to the amount of dynamics riding on this frontal boundary, even a small deviation would be able to turn a potential severe weather event into a heavy rain/flooding threat with very little notice-or vice versa.

The first threat of thunderstorm development will likely be in the early afternoon hours, with the second, and more impactful taking place towards the late afternoon/early evening hours. Regardless, all modes of severe weather will be possible on Friday, with damaging wind gusts, large hail, and even an isolated tornado being quite possible. Very heavy rain will also be a large concern as the atmosphere will be “water logged”-for the lack of a better term. Both time frames will likely need adjusting over the next 36 hours or so, so make to stay up to date with our daily updates.

This afternoons European model, showing very high precipitable water vales (PWATS), modest mid level winds, and an approaching mid level trough to help kick off a two-pronged event on Friday with severe weather and localized flooding possible.

This afternoons European model, showing very high precipitable water vales (PWATS), modest mid level winds, and an approaching mid level trough to help kick off a two-pronged event on Friday with severe weather and localized flooding possible.

This Weekend and Beyond

Improving conditions are looking likely heading into the weekend, with some clouds or showers may linger into Saturday morning as shortwave trough and frontal boundary exits the region. Otherwise high pressure from Ohio Valley builds into region with a drier northwesterly flow, for rest of the weekend. It will be more pleasant, with lower humidity, more sunshine and high temperatures in the lower to middle 80s. Latest GFS and ECMWF models are keeping the next chance of more scattered showers and thunderstorms with cold front and upper-level trough coming from Great Lakes, away until Monday or Tuesday. Temperatures will likely be at seasonable levels through early next week.

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Have a great evening!

Steve Copertino & John Homenuk

Steven Copertino

Public Analysis: Potentially Active Week Ahead With Multiple Thunderstorm Threats

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Good Evening! 

This morning we saw rather pleasant conditions set up over the area as an area of weak high pressure off the Mid Atlantic coast continues to back towards the east, which has been feeding in southerly/easterly winds from off the ocean. With relatively modest humidity and low level moisture, we saw partly cloudy skies with some more sustained periods of sunshine persist for locations well-removed from the coast. This partly cloudy environment, with a few more clear locations allowed high temperatures to rise into the low to middle 80’s across much of the area. Locations around Long Island and Connecticut saw slightly lower highs due to a more persistent southerly wind, bringing in more a maritime airmass.

For much of the afternoon this maritime airmass has kept a pretty stout lid on the atmosphere, not allowing any shower activity to develop, but as we can see from the loop below, the dew points (in green) have begun to rise quite a bit due to a weak surface warm front ahead of a mid level shortwave currently located over the Ohio Valley. This surface warm front has some very meager lift associated with it, and with the increased moisture advecting north, it seems likely that some showers and even a brief thunderstorms may develop this evening. Nothing too extreme is expected to develop outside of a locally heavy rain threat as the atmosphere remains in a minimally supportive environment for shower development.

After sunset, the complex located in the Ohio Valley that currently has numerous severe thunderstorm and tornado warnings will continue to move eastward in the aforementioned stable airmass. This will cause complex to weaken significantly, and there has already been a noticeable decrease in lightning activity noted on the regional mosaic. It appears that this afternoons model guidance has been rather poor with its overall performance in handling the shortwave responsible for generating these storms, but it appears that at the very least that an increase in clouds is expected for the Tuesday AM hours.

This afternoon/evenings latest high resolution visible satellite, regional radar mosaic, and surface observations showing some weak showers breaking out over New Jersey, with more showers and thunderstorms moving in from the Ohio Valley (Courtesy of Simuawips.com)

Tuesday Into Tuesday Evening

Tuesday morning looks to start off with partly sunny skies, with some heavier areas of cloudiness likely near the coast as moisture continues to increase in the mid to lower levels in the atmosphere through the early morning hours. This moisture will be coming in from the south and west as another shortwave trough and its associated mid level energy quickly moved east during the late morning hours and into the early afternoon. Earlier model guidance had this initial shortwave arriving later in the day on Tuesday, but as I mentioned earlier, these shortwave disturbances in the general flow over the country have not been modeled well, with all the disturbances actually progressing much quicker than originally thought.

So what does this mean for tomorrow? Well, with the first disturbance likely coming through around 11am-2pm, this will mean the area has much less time than originally thought to destabilize through daytime heating. Additionally, it will mean that any shower and thunderstorms that do form will also be able to use up any marginal parameter space that may be present by that time. After this initial passage of showers and thunderstorms, it will be crucial to see whether or not we can lose any left over cloud cover. With winds out of the south/southwest, conditions could be favorable for instability to once again rebound over the area, but this will be very highly dependent on how the initial morning shortwave behaves.

If the area does indeed destabilize to what the NAM and other computer model guidance shows, then forecast soundings from across NJ/NY/CT suggest that showers and thunderstorms could develop off to our west and then begin to gradually move east during the mid to late afternoon hours. As these storms move into a potentially more unstable airmass with modest levels of unidirectional shear, they could grow into mutil-cell clusters, as well as pulse-type cells. The main threat with these storms will be locally damaging winds, very heavy downpours, and even some small hail in the more intense updrafts. While not explicity likely, there may be just enough low-level turning in the atmosphere to support some more robust mesocyclones, but high cloud bases may preclude any outright tornado threat tomorrow. We will likely have to revisit this threat tomorrow morning and afternoon just to get a sense of what the overall threat will be after the initial shortwave passage.

This afternoons NAM model showing the area destabilizing quite nicely after an initial round of showers and storms moving through the area. The situation will have to be monitored closely tomorrow afternoon to gauge the overall threat

This afternoons NAM model showing the area destabilizing quite nicely after an initial round of showers and storms moving through the area. The situation will have to be monitored closely tomorrow afternoon to gauge the overall threat

Wednesday and Beyond

After a calmer and more seasonable day Wednesday, another disturbance approaches the region on Thursday with a surface low tracking north into Western New York State. While it is too early to discuss individual parameters, especially given the degree of uncertainty surrounding convective evolutions prior to the disturbances approach, it appears probable that another threat for strong to severe thunderstorms will evolve during the afternoon and evening hours throughout the Northeast.

Notable height falls are present on most models and ensembles during the afternoon and evening hours, with marginally favorable instability parameters (again including a modified elevated mixed layer and favorable surface instability. Future forecast shifts will have to monitor trends among ensembles and models to attempt to identify local threat regions.

The European model showing another shortwave trough setting up in the Great Lakes region, with multiple disturbances embedded in a west to east flow. This would make it possible for at least a few storm chances later in the week

The European model showing another shortwave trough setting up in the Great Lakes region, with multiple disturbances embedded in a west to east flow. This would make it possible for at least a few storm chances later in the week

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