Posts

John Homenuk

PM Update: Torrential rain tonight and Monday throughout New England

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Happy Sunday! We hope you have all been able to enjoy a lovely weekend — which, weather wise, turned out to be reasonably pleasant. This will change later this evening, and is already in the process of doing so throughout much of the Mid Atlantic. A warm front currently situated over the Northern Mid Atlantic states has served as the focal point for the development of thunderstorms this afternoon, but these are quickly merging into a larger-scale threat of heavy rain.

Heavy rain will continue to shift northward this evening as the warm front begins to respond to a developing impressive synoptic-scale storm evolution. A large and impressive shortwave disturbance is forecast to move northward from the Mid Atlantic into the Northeast, aiding in the development of widespread lift for heavy precipitation. This will allow a threat of heavy rain to spread northward from the Mid Atlantic into PA, NJ, and NY later tonight.

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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

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