Active Weather Pattern Ready to Begin

Warm and dry weather has dominated over the past 3 days.  For early August this is almost perfect weather.  That all changes tomorrow as hot and humid weather will return.  Some showers and thunderstorms are likely in Western and Northern New England tomorrow AM before shifting east late morning/early afternoon.  Thursday-Saturday will likely see heat advisories posted.  Let's break it down.

General Overview
As always let's start at the surface.  Notice high pressure over New England
WPC Surface Analysis 2 PM 
This will slide offshore tonight.  At the same time a weak upper level disturbance will slide along the US/Canadian border.  Here is tomorrow morning's upper level chart.  I've added a few features
18z NAM 500 mb vort 8 AM Wednesday (Image NCEP)
When the high pressure is centered offshore the source of our air mass is the Gulf of Mexico  The red line indicates the an upper atmosphere impulse that should fire off some showers and storms tomorrow.  Another way to look at this is the atmospheric moisture.  Here is this morning at 8 AM
12z GFS Precipitable Water/MSLP 8 AM Tuesday (Image Tropical Tidbits)
Here is tomorrow afternoon at 2 PM
12z GFS Precipitable Water/MSLP Wednesday 2 PM (Image Tropical Tidbits)
A small shift offshore results in big time changes to our weather.  Brown is dry air while the lighter yellow/green/blue are moist air.  That means that any showers or thunderstorms that do develop will be capable of heavy downpours.  Tomorrow 10 AM-4 PM is the greatest chance for showers in Southern New England.  This will hold true through Saturday. 

It will not be super hot tomorrow however.  Cloud cover will hold temperatures around 80.  That said dew points will run near 70 for a tropical feel to the air.  The clouds fade for Thursday and as a result temperatures will soar into the mid to upper 90's.
NWS NDFD 2 m max temps Thursday (Image Weatherbell) CLICK TO ENLARGE
With dew points near 70 on Thursday it feel close to 100.  There will be heat headlines such as heat advisory and possibly an excessive heat warning on Friday.  I expect Thursday and Friday to be mostly dry.  Saturday looks to be more active with showers/thunderstorms.  The high pressure in the Atlantic is strong.  It will slow down approaching cold fronts.  One should be close by Saturday however.
WPC Saturday 8 AM Surface Forecast 
The tropical air will still be around.  There will be widely scattered showers/thunderstorms.  Although I wouldn't cancel anything yet I'd start thinking of moving outdoor plans indoors.   The heat will still be around Saturday until this front moves through.   A concern of mine (but not all that concerning) is that the front stalls near New England.  That would mean waves of low pressure track through New England providing a soaking rain.  I get people work all week and want to enjoy their weekend but we need a soaking rain.  I'm watching it.  

We'll chat soon.

-Zack Green


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