Friday, February 15, 2013

Snow Saturday-Sunday? At Least Some

I am not expecting a storm like the Blizzard of 2013 on Saturday.  But believe it or not that storm was easier to forecast than this weekends event.  The EURO had locked onto the blizzard from about 5 days out and did not waver.  It was case closed for me even though the GFS never really came around and the NAM was iffy until 36-48 hours out.  This time there is no real consensus so forecasters are on our own.  First of all the overnight guidance cannot even agree on when the precipitation begins.  Secondly some models still develop a nor'easter while others are a weaker more strung out system.  Finally other models show pretty much nothing.  It doesn't mean the forecast is impossible, it means I have to use my brain like forecasters did BEFORE computer models.

Current Conditions
HPC surface chart 523 AM
A cold front is dropping south through the Midwest.  Another boundary is present through Texas and has several waves of low pressure.  This is likely the first issue the model is having- lots of energy in the stream.  At 500 mb we look like this
09z RAP 500 mb vort (NCEP)
A ridge has developed along the west coast and has good amplification.  One would expect the trough to deepen all the way to Florida.  This much of the forecast is certain; heights will be lowering across the east.  Currently on radar the nation looks like this
National Radar image 620 AM
Finally here is the 300 mb jet stream
06z NAM 000 300 mb winds 
The momentum created by the jet streak near Alaska will be the primary cause of the trough deepening in the east.  The southern stream is awfully close to the northern stream, which often happens in February.  The streams will phase but I believe it will be too late to give us another blizzard.  However I do believe that tomorrow the first wave generates enough forcing and lift and a snow event breaks out.  

Friday
No problems today; temperatures will get close to 50.  Today is a good day to get rid of any leftover ice from the blizzard.

Saturday
Snow begins to fall in the morning and will continue at a light-moderate clip for most of the day.  HPC has a 40% chance of 4 inches of snow from 7 am Sat-Sun
HPC day 2 prob > 4" snow
The EURO operation is advertising a general 3-6, a lot more for Maine.  Here are the totals through Monday morning
00z EURO op total snowfall (image weatherbell)
Again tough call, but going with a weaker, long duration storm.  It will snow throughout Saturday night into Sunday.  Whatever hits should be out by noon on Sunday.  There is still a chance of a complete miss and a complete hit; I just find those odds low.  I'll update later to either confirm my forecast or blow it up.









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