Wednesday Update

When watching the news or searching facebook it is important to know who is providing the information and where it is they are talking about.  No one in Southern New England is promising 2 feet of snow unless it is a 12 year old wish casting online.  When the news is talking about a historic storm they are referring to the DMV (DC, Maryland, Virginia).  See my post yesterday for a larger discussion on the evolution of the storm.

General Overview 
The energy that will be responsible for the storm is now onshore.  It is a weak frontal system in the Pacific Northwest.  This energy will dive southeast towards the four corners and combine with another piece of energy in Texas (circled).
06z NAM 500 mb vort 1 PM Wed (image NCEP)
This will lead to a surface storm that should produce showers and thunderstorms along the Gulf Coast states.
WPC surface forecast Thursday 7 AM
We went over this yesterday.  So now the question is why won't the storm come all the way up the East Coast?  The first answer is it develops and closes off too quickly.  Let us review the 2015 January Blizzard 500 mb set up and also show the set up for this storm.

First up- 1.25.15
Notice how the energy is much further north.  The ridge out west is more pronounced and this energy is already ready to round the base of the trough.
1.25.15 12z NAM 500 mb vort for 7 am (image NCEP)
 Now I want to show the storm as it gets to the east coast.  The trough has a strong negative tilt but the low has not yet closed off yet at 500 mb
1.25.15 12z NAM 500 mb valid at 7 PM Monday 1.26 (image NCEP)
Now let me show you what the surface looked like at 7 PM that Monday night.

WPC surface analysis Monday January 26, 2015 7 PM
In contrast when the 500 mb trough is in a similar location Friday look at the huge differences
12z GFS 500 mb vort valid Saturday 7 am (image NCEP)
The low is already closed off so meteorologically speaking the storm is peaking.  This is when DC, Balt, Richmond etc are being pounded with snow.  Here is the surface chart forecast for Saturday AM
WPC surface forecast Saturday 7 AM
 Why won't this storm just continue up the coast?  First of all the high pressure in Quebec will help force it to the east north east.  The upper level system will start to be elongated as well and multiple low pressure centers will form.  This lows will compete for the energy and odds are one of the lows closer to the gulf stream will win out.  From experience I was burned in a situation like this in 2010.  I was in college in Advanced Forecasting and the Mid Atlantic was forecast to get a huge snowstorm.  We believed it would come up the coast and give Southern New England a good 8-12 inches of snow.  Nearly the entire class busted.  If the upper level low looked like this
12z NAM 1.25.15 valid Tuesday January 27, 2015 (image NCEP)
THEN PERFECT!  Unfortunately by Sunday morning it will look something like this
12z GFS 500 mb vort valid Sunday 7 Am (image NCEP)
 With all those competing maximums snow will not make it very far into Southern New England, if at all.
12z GEFS snowfall through Sunday 7 PM (image weatherbell)
Very few members have any snow at all and this has been consistent for days.  This is a DC snow storm which happens in El Nino's.  So my call is this..
Snowcast props
 I am honestly being generous.  It's probably a 5% chance of a plowable snow from the MA/CT/RI border to the pike, if that.  The snow would fall Saturday PM if it does so I'll keep an eye on it but my recommendation is to keep all plans.   For entertainment here is the storm I busted on in 2010
Feb 4-7 nor'easter 2010 NESIS
The map should look similar when all is said in done (just shifted south a bit).

As always questions, comments, complaints, concerns on facebook or twitter.  One more update tomorrow to officially write this one off.

-Zack Green


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