Update on Pre-Thanksgiving Day Storm

11/23 4pm
Pre-Thanksgiving Day Storm

It's time to start talking about potential impacts from the upcoming pre-Thanksgiving day storm. While there are still uncertainties in regard to the exact track of the low (which will be huge in determining who sees rain vs. snow and how much), this system looks like a sure bet to cause travel headaches up and down the east coast.  If you have travel plans, this is definitely one you'll want to keep an eye on.  This summary will be geared towards Shenandoah Valley locations.

Shenandoah Valley Breakdown

What we know:

• Set-up: A cold front will swing through Monday night before stalling somewhere off the coast Tuesday.   A strong piece of upper level energy will dive across the central portion of the country into the Gulf, helping to form an area of low pressure off the coast of Florida Tuesday night.  This low will track northeast up the coast along the temperature gradient spreading precipitation across the eastern seaboard.

WPC-Wednesday Surface Map

• Timing: The time frame for us will be pre-dawn Wednesday through late Wednesday night

What we don't know:

• Exact Track: Here we are less than 72 hours from the start of the storm and there is still lots of uncertainty in regards to the track of this system.  Models seem to be clustering into two different camps 
• Camp # 1: (Canadian, NAM, SREF mean, JMA, upgraded GFS, NAVGEM) Storm takes too long to get going with flow too progressive.  Storm stays too far off the coast for much precipitation to spread west enough to impact us in the Shenandoah Valley.  Light rain/snow showers or flurries possible.  Minimal impacts.

12z Canadian (AccuPro)

• Camp # 2: (European, European Ensembles, UKMET, and to some extent- the regular GFS) Storm gets its act together off the Carolinas and tracks right up the immediate coast.  Precipitation spreads all the way into West Virginia; moderate to heavy at times across the Shenandoah Valley.  These better rates help draw down colder air from aloft (dynamic cooling), making this a mostly snow event across our area. This would result in accumulating snows (generally 4-8", although the Euro is more like 8-12").  

12z GFS (AccuPro)

Current Thoughts: 

While a few of the typically reliable models (Canadian and JMA) are still wide-right with this system, it's really hard to discount the consistency of the Euro and its ensemble mean at this range.  I don't see the hefty amounts on the Euro (8-12") working out, but I do think this ends up being a bit more than the "brush" I previously thought.  If I was put on the spot right now, I'd go with 2-5" across the Valley with a few inches added to that across the higher elevations.  I will have a first call snow map out sometime Monday evening that will include projected amounts for the entire state.  Remember this is a low confidence forecast and subject to change over the next few days.