2:00 PM | **Wild weather pattern to bring about big east coast storm threat, tropical activity, and an impressive cold shot**

12Z GFS forecast of 500 mb height anomalies from Friday morning until Tuesday morning (6-hour increments) featuring the development of deep upper-level low pressure in the eastern states; courtesy tropicaltidbits.com, NOAA/EMC

Overview
The wild weather pattern we talked about last week has begun to unfold and the eastern US will have some very interesting weather later this weekend and early next week.  A significant rain event is increasingly likely for the Mid-Atlantic region late in the weekend as deep upper-level low pressure forms in the eastern US and strong surface low pressure develops near the coastline.  This potential major coastal storm may very well be juiced up by tropical moisture as the western Caribbean Sea is currently showing some life and this particular tropical system may just ride up along the east coast and get entrained into the coastal storm.  

In the meantime, cold air will be charging to the southeast by the latter part of the weekend across the Upper Midwest and Great Lakes. This incoming cold air mass will also get involved in the overall pattern and the result could be some snow accumulation in the higher elevations of West Virginia and southwestern Pennsylvania.  The colder-than-normal air that arrives on Monday in the I-95 corridor behind the passage of a strong cold front looks like it’ll stick around for awhile including for Halloween day (Tuesday).  In fact, the first half of November is likely to feature multiple cold air outbreaks for the central and eastern US.

12Z GFS forecast map for early Sunday afternoon with strengthening low pressure off the Carolina coastline; courtesy tropicaltidbits.com, NOAA/EMC

Discussion
The weather stays relatively calm during the next few days around here, but the weekend will see the approach of upper-level energy in the eastern states and a deep trough will develop by early next week.  At the same time, a strong cold front will drop southeast this weekend across the Upper Midwest and Great Lakes and tropical moisture associated with “Invest 93L” is likely to ride northward from the Caribbean Sea into the western Atlantic – not far at all off the US east coast.  The result is likely to be a significant rain event for the eastern seaboard from late Saturday night into Sunday night and this potential major coastal storm will be followed by a cold air outbreak on Monday.  

An area of showers and thunderstorms in the western Caribbean Sea is now officially known as "Invest 93L".  The moisture from this tropical system could very well play a role along the east coast during the upcoming weekend. If this system intensifies and becomes a named tropical storm, it would be "Phillippe"; image courtesy NOAA/GOES

Following the cold frontal passage, strong northwest winds are likely to usher in much colder air to begin the new work week and the chill should stick around on Halloween Day (Tuesday). Temperatures on Halloween evening could be in the 40’s along much of the I-95 corridor. Additional cold air outbreaks are likely during the first half of November for the central and eastern US – quite a change from the month of October which has been well above normal in terms of temperatures. 

12Z GFS forecast map of total snowfall by next Tuesday with some accumulations showing up over West Virginia and southwestern Pennsylvania; courtesy tropicaltidbits.com, NOAA/EMC

Stay tuned…going to be quite an interesting couple of weeks.

Meteorologist Paul Dorian
Vencore, Inc.
vencoreweather.com