Showers, Thunderstorms likely Thursday PM

A upper level disturbance will move over New England tomorrow afternoon.  Cold temperatures in the upper atmosphere will combine with a warm surface to produce numerous showers and thunderstorms.  The thunderstorms will be capable of gusty winds and small hail.  High pressure will build in again Friday before we begin a transition to cooler/wet Saturday PM.

Overnight a few sprinkles will fall in Southern New England.  Temperatures stay in the mid to upper 40's.
NWS NDFD Minimum Temps Wednesday Night (image Weatherbell)
Here is the upper air (~18k ft) at 8 PM.  Notice the depression around the Great Lakes.  This is the upper level trough that will move over New England tomorrow.
18z NAM 500 mb vort 8 PM Wed (image NCEP)
Here is the same chart valid 5 PM tomorrow.  The trough is directly over New England.
18z NAM 500 mb vort Thursday 5 PM (image NCEP)
So why would this cause thunderstorms in the absence of a cold front?  Here are the temperatures at 500 mb.
18z NAM 500 mb heights, temps Thursday 5 PM (Image College of Dupage Weather Center)
Now it won't be hot by any means tomorrow but temperatures should get to the low 70's which is close to if not a few degrees warmer than average.  None the less this large difference in surface temperature and upper air temperature will allow for air parcels to become unstable tomorrow afternoon.
NWS NDFD 2 m max temp Thursday (image Weatherbell)
Showers and thunderstorms develop around 1-2 PM in VT, NH and W MA.  This moves into Worcester county around 4 PM.  By 5 PM high resolution weather models show a lot of activity in NH and C MA.
18z NAM simulated radar Thursday 5 PM (image credit College of Dupage Weather Center)
The activity moves towards Boston by 8 PM but it will weaken.  Thursday night is fairly nice as temperatures will drop to about 50.  Friday is very nice as high pressure sits over the region.  Expect temperatures in the mid 70's.  Saturday AM looks pretty good as of now but all eyes are on a system to our south for Saturday PM into Sunday.

More details on the weekend tomorrow.  I'll keep an eye on the radar/sky tomorrow.

-Zack Green


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