Sunday, February 15, 2015

First Call for Monday-Tuesday Storm

(7pm update)
After going over the afternoon guidance, went ahead and upped areas discussed earlier.  I still have concerns regarding the effects of dry air east of the mountains but can't ignore model guidance consistency at this point.  One last final call will be out by 8 am Monday morning.

A few other important points (mentioned on Facebook Page already):

  • Due to this recent arctic blast, surface temperatures (including roadways) are well below freezing. When snow starts falling, it's going to start sticking right away...certainly not something you'll want to be out driving in. I hope schools/businesses take this into account while making decisions for tomorrow.
  • After this storm departs, temperatures will struggle to make it above freezing across a lot of the area through the rest of the week. In fact, another arctic blast similar (actually likely even colder!!) to the one we're seeing today will arrive Wednesday and last through the end of the week. Put tomorrow's snow and the next blast of arctic cold together and looks like school kids will be pretty lucky this week.

Second Call Map for Monday-Tuesday


(Posted 1pm)

Low pressure will form along the Gulf Coast early Monday morning before tracking northeast through the Carolinas.  Precipitation spreading north of this system will override very cold, arctic air currently in place over the mid Atlantic leading to a period of wintry weather.  Recent trends suggest a more northerly tracking low leading to a few things:  1) increased sleet and freezing rain potential along and south of the Virginia/North Carolina border and 2) increased snowfall totals across the northern 1/3 of the state including the entire Shenandoah Valley and Fredericksburg/DC areas.  It looks like the heaviest snow will fall across the higher elevations of southern West VA and southwest VA where upslope enhancement comes into play.  Models suggest I may be under-doing snow amounts across much of central Virginia.  My reasoning for that is the fact this will be a relatively quick hitting system that'll have to overcome quite a bit of dry air initially (dew points likely in the single digits or lower)...will have an updated final call with any necessary changes out later this evening or tomorrow morning.

Shenandoah Valley General Thoughts:

Timing: A lot of above-mentioned dry air in place will cause much of the initial precipitation to fall as virga, drying up before it reaches the ground.  My best guess at onset is between 1 and 4 pm....starting southwest to northeast.  Snow will become steadier through the evening hours with the heaviest between 7pm Monday and 5am Tuesday.  The storm will taper off west to east during the mid morning hours.  

Amounts: I do expect this to remain all snow here.  A general 3-6" is a good bet across the southern and central Valley with 1-3" further north.  I do think there will be isolated higher amounts (won't be surprised to see a 8-10" report or two, especially in surrounding mountain locations).  

Uncertainties: Thanks to what looks to be a pretty sharp northern QPF cutoff, will have to adjust the 3-6" line north  or south based on how far north the low tracks.  In other words, the 1-3" over the northern Valley may very well need to be upped to 3-6" in my final call. 

First Call Map for Monday-Tuesday

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