Temperature Roller Coaster Ride

Low pressure working up the coast, a cold front driving east, and high pressure exiting off the coast will contribute to some wild temperature swings over the next 2-3 days.  The low pressure system will bring some precipitation to the Cape and Islands, the cold front will bring precipitation to the rest of us.  Behind the cold front seasonable temperatures return.

Observations/Short Term Forecast
The radar shows rain just off the New England coast this morning.  Martha's Vineyard and Nantucket are already raining

NWS Northeast Regional Radar 508 am

Here is the storm on the water vapor satellite.  You can also see the high pressure exiting into the North Atlantic/Canadian Maritime and the cold front progressing east

NOAA GOES_E Water Vapor Satellite 445 am 

For a more traditional look here is the surface chart

WPC surface analysis 330 am

Temperatures this morning are running in the mid 30's in Southern New England.  

4 am 2 m temps (image weatherbell)

There will not be much of a warm up today.  In fact it will be pretty miserable.  The winds will not be strong, but they will be steady and out of the Northeast at 10-15 mph.  Here is what I am thinking around 4 PM

06z NAM Hires 2 m temps 4 pm (image weatherbell)

Temperatures will max in the mid 40's.  Southern RI and CT may be able to get close to 50 as the RAP is indicating.  A steady stream of rain will work into SE MA.  The heaviest rain will arrive this evening.  Here is the simulated radar image for 11 PM

06z NAM hires simulated radar 11 pm (image weatherbell)

All in all the one day precipitation totals look like this

WPC 1 day precipitation outlook 

The outer cape could see up to 1.5 inches of rain while Worcester County sees nothing.  The low will move into the Gulf of Maine tomorrow afternoon which sets up an interesting scenario.  Usually when there is low pressure in the GOM in spring/early summer a classic back door cold front (BDCF) develops (h/t Dr. Colby).  Here is where the EURO likes the low tomorrow afternoon.  Since flow is counter clockwise around a low, it would make sense that a localized temperature gradient will develop.

00z EURO precip 2 pm Wed (image weatherbell)

As of now the NAM hires likes that BDCF to stay in Maine and most of Southern New England soars into the upper 60's/low 70's.

06z NAM 2 m temps 2 pm Wed (image weatherbell)

The EURO is not as warm.  So what I believe happens is that it warms up early outside of 495 and takes a bit longer in Eastern MA.  It may never get warm along the coast tomorrow.  As you can see on the temperature chart above there is a sharp gradient which is the cold front.  Here is 8 PM tomorrow

WPC surface forecast 8 pm Wed

While the cold front looks ominous, it should weaken as it gets to New England.  The precipitation will be breaking up as it passes by Wednesday night into Thursday morning.  The long range looks seasonable with temperatures, but abnormally dry.  My sense is that May is not all that dry, so lets enjoy it while we have it.