Doug Simonian

Medium Range Analysis: Severe Weather Chances this Weekend

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Good evening! We hope you all had a great Monday. For the most part, the area had a beautiful, summer day, but some western suburbs of NYC had some strong thunderstorms and flash flooding. These storms quickly weakened as they headed towards NYC, as the pattern right now is generally not favorable for severe weather in our area. But that may change come this weekend, when the general synoptic pattern may start to favor strong to severe thunderstorms.

It’s pretty far out in time, so plenty can change — but at this range we like to look at general features of the pattern and what they signal, since there is inherently less noise in broader signals. One thing we like to look at is a pattern that can favor advection of an EML (Elevated Mixed Layer) into the region. The EML is a layer of very hot and dry air from around 700mb (around 10,000 feet) and up that originates in the desert southwest. This hot and dry air air is not contaminated with moisture and thus it can cool quickly with height, creating a lot of mid-level instability. These EMLs often combine with rich, tropical Gulf of Mexico moisture in the low-levels of the atmosphere in tornado alley and lead to some of the biggest severe weather outbreaks.

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John Homenuk

AM Update: Calm start, but transitional weather ahead

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Good morning and Happy Monday to you all! As you make your way out the door this morning, you’ll notice a change to the sensible weather conditions in place throughout the majority of the Northeast states. You can thank a strengthening south/southeasterly flow for that — it has replaced the cooler, northwest breeze with a warmer and slightly more humid airmass. Warmer and more humid air will advect into the Northeast states for the remainder of today.

Near the coast, these southeasterly winds have already resulted in the presence of some stratus clouds along the shores of Long Island and even parts of New Jersey — with some localized fog in other locales as well. This will burn off as the day goes on, but the progression of disturbances in the mid and upper levels of the atmosphere will bring more unsettled weather into the picture by this afternoon.

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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.

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

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.

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 & John Homenuk