Another Winter Storm Thursday

Are you sick of winter yet?  It has been a remarkable winter so far for the Eastern 2/3 of the United States.   Another winter storm will impact Southern New England on Thursday.

Overview
A Polar Front has reached the Gulf Coast as a large dome of high pressure built up in the middle of the country.  Here is the 1 PM Surface Analysis

WPC 1 PM Surface Analysis

Here is the US temperature map as of 4 PM

4 PM 2 m temperatures (image Weatherbell)

The Jet Stream splits into a Northern and Southern stream in the west.  One stream is in Southern California through Arizona and New Mexico while the other enters the US in Washington.

18z NAM 1 PM 300 mb heights/winds (image NCEP)

Embedded within both streams are pieces of upper level energy.  These show up nicely on the 500 mb chart (I've circled the two pieces to watch)

18z NAM 500 mb vort 1 PM (image NCEP)

Both pieces also show up on the water vapor satellite 

GOES_WEST Western US water vapor image 5 PM

The Southern piece of energy will slide east through Arizona, New Mexico, and Texas towards the Gulf Coast while the Northern piece slides southeast through Montana, South Dakota, Nebraska, and Missouri.  The Southern piece will deliver quite a blow to the South on Wednesday.  This is after they get through several waves of low pressure tomorrow.  Locally the weather is quiet tomorrow and Wednesday.

Tuesday Cold tonight with mostly clear skies.  Low temps 5-10.  Mostly Sunny during the day, highs 20-25.  Very cold Tuesday night, expect low temps -2 to 4 above. West wind could gust 15-20 mph so wind chills around 0 are likely.  

Wednesday Cold again with mostly sunny skies.  Temps 20-25 with a light north wind.

By Wednesday morning a healthy storm will have formed along the Gulf Coast.  The Northern stream energy will not have combined with the Southern stream yet.  

Wednesday 7 am surface forecast WPC

Here is the 500 mb chart as of Wednesday 10 am

18z NAM 500 mb vort 10 am Wed (image NCEP)

By Thursday morning a coastal low will be moving up the Atlantic Seaboard

WPC Sutface Forecast Thursday 7 am

By 1 PM on Thursday here are the upper level charts

18z NAM 300 mb heights, winds 1 PM Thur (image NCEP)

Notice the blue streak off the Mid-Atlantic coast? That is driving a closed 500 mb low

18z NAM 500 mb vorticity 1 PM Thur (image NCEP)

This upper level set up favors a deepening area of low pressure moving just South and East of the Cape/Islands. A lot of precipitation will fall with this system and strong winds will move across Southeastern New England.

Snowfall Amounts

60 hours out is too far for me to make a map.  I am confident in heavy precipitation and at least 3-6 inches of snow for most outside of 95.  I'm also confident in strong winds gusting to 60 mph in Southeastern MA/Cape and Islands.  Where the rain/snow line sets up is a tough call.  There is no high pressure to the north to lock the cold in.  However there is a deep snow pack and the Atlantic is about as cool as it can get around here.  

Precipitation Type Expectation 02/13/14

The storm looks to start around 7 am on Thursday.  The morning looks to be all snow for everyone except the Outer Cape and Nantucket.  The storm will wind down early Friday morning.  I'll have the accumulation map tomorrow.  Have a good one.

-Zack Green