Thursday, May 2, 2013

Warm Afternoon, Rapid Temperature Drop This Evening

An upper level disturbance will retrograde from Newfoundland to a location off of SE New England today shifting winds and dropping temperatures tonight and tomorrow.  A sprinkle or brief shower cannot be ruled out early this evening as a back door cold front pushes west across New England.  The 70 degree weather will return early next week after a bright weekend with temperatures in the mid to upper 60's.

Short Range Forecast/Observations
Temperatures are in the mid to upper 40's this morning
4 am 2 m temps (image weatherbell)
Here is the projected 8 am surface chart.  Notice the high pressure placement
WPC 8 am surface forecast
Winds in SNE will generally be light early in the day.  As the front pushes by winds will flip to the Northeast.  Heres a look at the winds at 11 am.
06z NAM 10 m winds, direction (image weatherbell)
You can click to enlarge but the wind direction is highly variable.  Here are the max temperatures early this afternoon. This model has a bit of a warm bias, but its been doing well as of late
09z RAP 2 m temp 2 pm (image weatherbell)
That is widespread mid to upper 70's.  Someone (Bedford, Salem, NH?) will approach 80.  But temps will begin to drop around 5 pm at the coast and will push south and west rapidly this evening.  Here is the simulated radar at 6 pm
06z NAM hires simulated radar 6 pm (image weatherbell)
Here is the temperatures at 8 pm
06z NAM hires 2 m temps 8 pm (image weatherbell)
It is still close to 70 in Springfield at 8 pm, but only 50 in Boston.  That's a hell of a gradient as you drive down the Pike.  Here are the low level winds at the same time.  Remember earlier in the afternoon they will be light and variable
06z NAM 10 m winds, direction 8 pm (image weatherbell)
Now the winds are directly from the east and stronger.  So what is causing this? Let's go to the 500 mb chart to see.  This is the 500 mb off the Canadian model at 2 am this morning
00z CMC 500mb vort 2 am (image weatherbell)
Notice the blob in the top right corner?  Now check that out at 8 pm
00z CMC 500mb vort 8 pm (image weatherbell)
The low has retrograded, or backed, close to the New England coast.  That will push the high pressure that has been supplying us with such good weather away for 24-36 hours.  Tonight temperatures will fall to the low 40's.  Tomorrow we will still be under the influence of northeasterly winds
06z NAM 10 m winds, direction Fri 2 pm (image weatherbell)
That will keep temperatures in eastern New England around 60
06z NAM hires 2 m temp Fri 2 pm (image weatherbell)
A stray sprinkle cannot be ruled out tomorrow.  The weekend forecast from yesterday is on track so please see my previous post for that.  Enjoy your Thursday!

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