**Dry spell ends on Thursday night with cold front #1 and numerous showers and thunderstorms...cold front #2 brings another round of showers and thunderstorms late Saturday/Saturday night**
Paul Dorian
While not everyone gets soaking rainfall on Thursday night, there will be numerous showers and thunderstorms in the Mid-Atlantic region breaking the dry spell of recent weeks with 0.25 to 0.50 inches commonplace. This initial round of rain will be associated with a weakening cold frontal system and then a second and stronger cold front will bring additional showers and thunderstorms to the region from late Saturday into Saturday night. Map courtesy NOAA, tropicaltidbits.com
Overview
The month of August was not only quite a bit cooler-than-normal in the Mid-Atlantic region (coolest in 25 years in DC, 3rd coolest in 25 years for NYC), but it was also very dry as well in many areas. In fact, the DC-to-Philly-to-NYC corridor saw virtually no rainfall during the last ten days of August and the month of September has started off rain-free as well. There is plenty of hope, however, that in the near-term there will be two chances for some welcome rainfall associated with two separate cold frontal systems. The first chance of showers and thunderstorms will come late Thursday and Thursday night with the initial cold front and then a second round of showers and thunderstorms is likely for late Saturday/Saturday night associated with cold front #2.
The month of August was very dry across much of the Mid-Atlantic region and also cooler-than-normal. In fact, it was the coolest August in 25 years in the DC metro region, the 3rd coolest in NYC during the past 25 years, and the 6th chilliest since the late 1800’s across Chester County in southeastern Pennsylvania (courtesy @ChescoWx).
Details
We’ve experienced some very dry stretches of weather in the Mid-Atlantic region during the past year or so including an October of 2024 that managed to produce virtually no rain at all in the Philly metro region. The just ended month of August was not only quite a bit cooler than normal in the Mid-Atlantic region, but it was also very dry as well in many locations with, for example, only 0.20 inches in the DC metro area (DCA) for the entire month. September has started off with a continuation of dry, comfortable conditions in the Mid-Atlantic region, but the next few days will present some important changes.
An initial cold frontal system will usher in an unseasonably chilly air mass into the Northern Plains/Upper Midwest/Great Lakes on Thursday and it is likely to produce some well needed rainfall in the Mid-Atlantic region and Northeast US from late Thursday into Thursday night. Map courtesy NOAA, tropicaltidbits.com
To begin with, the overall humidity, which has been exceptionally low in recent weeks, will begin to become more noticeable again during the Thursday, Friday and Saturday time period. In addition, temperatures will climb back to more uncomfortable levels with mid-to-upper 80’s on the table in some spots for afternoon highs during the next few days.
A second cold front will usher in a reinforcing unseasonably chilly air mass into the central and eastern US and it is likely to produce another round of much needed rainfall in the Mid-Atlantic region and Northeast US from late Saturday into Saturday night. Map courtesy NOAA, tropicaltidbits.com
The increase in warmth and humidity on Thursday will come ahead of a cold front that will cross the Great Lakes and head towards the eastern seaboard. This front has ushered in a much cooler than normal air mass to the Northern Plains and Upper Midwest with temperatures some 15 to 25 degrees below the averages for early September. This front will lose some of its punch as it arrives in the Mid-Atlantic region on Thursday night; however, it should still be able to produce some showers and thunderstorms...perhaps even a few strong thunderstorms and brief downpours. Rainfall amounts of 0.25 to 0.50 inches are probable in many spots along the DC-to-Philly-to-NYC corridor with this first cold frontal system and likely during the second event as well.
A widespread much cooler-than-normal air mass will encompass much of the eastern half of the nation by the time we get to the second half of the weekend. This air mass is likely to produce numerous record or near record lows from later this week into the weekend; especially, across the Northern Plains, Upper Midwest and Great Lakes regions. Map courtesy NOAA, tropicaltidbits.com
Meanwhile, a second cold front will push across the Northern Plains/Upper Midwest from later Thursday into Friday and it’ll usher in a reinforcing blast of unseasonably chilly air for those areas. This second cold front will push into the eastern states later Saturday and increase the chance for some PM shower and thunderstorm activity…some of the storms can be strong-to-severe and some of the rain can be briefly heavy. Following its passage, the unseasonably cool air mass from the Northern Plains/Upper Midwest will spread eastward on Sunday into the Mid-Atlantic region and temperatures will return to below-normal levels to close out the weekend and for the early part of next week.
Meteorologist Paul Dorian
Arcfield
arcfieldweather.com
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