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12:50 PM | *Heavy rain event coming for DC, Philly, and New York City...could be accompanied by strong thunderstorms…an extended stretch of colder-than-normal weather to follow*

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Weather forecasting and analysis, space and historic events, climate information

12:50 PM | *Heavy rain event coming for DC, Philly, and New York City...could be accompanied by strong thunderstorms…an extended stretch of colder-than-normal weather to follow*

Paul Dorian

 12Z GFS forecast map of 500 mb height anomalies for Friday morning; map courtesy tropicaltidbits.com, NOAA/EMC

12Z GFS forecast map of 500 mb height anomalies for Friday morning; map courtesy tropicaltidbits.com, NOAA/EMC

Overview
Two big weather stories going forward for the DC, Philly and New York City metro regions: (1) a heavy rain event is coming from later tomorrow night into Friday and it can be accompanied by strong thunderstorms and (2) an extended period of colder-than-normal weather from this weekend into the latter part of next week.  This chilly stretch of weather could even result in accumulating snow in some of the higher elevations of the Mid-Atlantic region as well as in portions of the Ohio Valley and Great Lakes.  Strong low pressure will form tomorrow in the south-central states - aided by tremendous upper-level energy - and then push northward towards the eastern Great Lakes.  Colder-than-normal air pushes in this weekend following the passage of a strong cold front and thanks to the formation of a classic “omega”-shaped blocking pattern in the upper atmosphere, it will stay colder-than-normal for several days.

 12Z GFS forecast map of 850 mb height anomalies for Friday morning; map courtesy tropicaltidbits.com, NOAA/EMC

12Z GFS forecast map of 850 mb height anomalies for Friday morning; map courtesy tropicaltidbits.com, NOAA/EMC

Heavy rain event
Deep upper-level low pressure will intensify over the next couple of days in south-central US and spawn the formation of strong surface low pressure.  This strengthening low pressure system will move towards the Great Lakes region and it should have a deep connection to the Gulf of Mexico which will increase the amount of tropical moisture available to the overall system.  On Thursday, heavy rain and potential severe weather can take place in the Southeast US and then rain should overspread the DC-to-Philly-to-NYC corridor later Thursday night.  A soaking rain will continue into Friday in the I-95 corridor and there can be some strong thunderstorm activity as warmer air pushes north along the eastern seaboard in the warm sector of the storm.  The heavy rain could even negatively impact the Friday morning commute in parts of the I-95 corridor.  By the time the rain winds down late Friday, there should be rainfall amounts of between 1.25 and 2.00 inches in much of the area from DC-to-Philly-to-NYC.

 12Z GFS forecast map of 500 mb height anomalies for Friday morning; map courtesy tropicaltidbits.com, NOAA/EMC

12Z GFS forecast map of 500 mb height anomalies for Friday morning; map courtesy tropicaltidbits.com, NOAA/EMC

Extended stretch of colder-than-normal weather 
Once this low pressure system grinds its way into the Northeast US, it’ll become part of an overall “omega”-shaped blocking pattern in the upper atmosphere and this will assure very slow movement and result in an extended period of chilly weather.  The classic signature of an “omega”-shaped blocking pattern this time of year is to feature deep upper -level low pressure near both coasts with abnormally high pressure ridging in the central US and that will indeed become the look by next week.  

The colder-than-normal conditions may also result in some accumulating snow in the higher elevation locations of the Mid-Atlantic this weekend as well as in portions of the Ohio Valley and Great Lakes.  With deep upper-level low spinning around over the Northeast US, the weather in DC, Philly and NYC will remain on the unsettled side with occasional showers this weekend to go along with the unusual chill for this time of year.  Temperatures can drop to as much as 20 degrees (C) below normal by the early part of next week.  

Meteorologist Paul Dorian
Vencore, Inc.
vencoreweather.com

Extended video discussion: