Late week Ohio Valley/Mid-Atlantic snowstorm

Thursday update:

Water vapor imagery shows the upper trough digging into the south-central U.S.

Winter storm warnings cover 52 of West Virginia's 55 counties (tip of Northern Panhandle excluded).  Major models have converged.  There's fairly high confidence in enough snow to make road travel extremely difficult or impossible and cause power outages.  Exact snowfall totals only matter so much beyond the point where everything shuts down, and much of the state can expect to reach that point.

The NAM has sharpened the temperature gradient at 700 mb (about 3 km above ground), focusing warm advection into a narrower band.  If this verifies, areas under that band of enhanced ascent will see snowfall rates pushing 2" per hour for several hours Friday night.  Plows and salt can't keep up with that.


Wednesday morning update:

Snow lovers rejoice!

NWS Charleston has covered all but the southernmost areas with a winter storm watch for 6"+ in the lower elevations and 12"+ in the mountains.  These are conservative, no-hype numbers.

Models are converging on the Euro's original idea of the surface low's track.  A more southerly track will mean less of a chance for other precip types to mix in.  There might still be brief intervals of sleet in southern WV, but the greatest ice accumulation should remain well south of the state.  This track brings ever so slightly colder air, such that a terrain-induced warm wedge west of the high elevations is less likely to take a big bite out of accumulations.  Furthermore, the track of the second surface cyclone up the Atlantic coast--the nor'easter--puts WV in a good place to catch wraparound snow on the back side all day Saturday.

Let's look at Weather Prediction Center probabilities...

I-64 corridor from Huntington to Charleston, that's a 50/50 shot at reaching a foot.



Original Tuesday morning post:

Take-home points:

1. Enough snowfall to make travel extremely difficult or impossible across most of West Virginia is looking more and more likely.  Forecast models are trending toward a storm comparable to the major snows of last winter.  Be prepared by Thursday evening.

2. Take forecasts of enormous snow totals with a grain of salt for the next 24 hours.  The big numbers being spewed out by some models are entirely possible, but there are a couple different ways the storm could realistically fail to produce accumulating snow for some of WV.

3. A relatively small swath of western/southwestern/central WV may see some ice accumulation.  A few power outages could result.

For specific point forecasts, NWS Charleston is here: http://www.weather.gov/rlx/.

Details:

West Virginia, the hype is more or less real.  Major models agree that heavy snow is likely for most of the state between Thursday night and Saturday morning.

However, we're 3-4 days out.  Forecasting a fast-moving, amplifying wave at this range relies almost exclusively on numerical models.  The upper wave responsible for the storm?  Still off the West Coast, where weather balloons can't sample it and we're dependent on satellite data.

Upper wave over the Pacific that becomes eastern U.S. snowstorm in major models

One reason I'm not comfortable promising a huge snowfall for WV at this point is the likelihood of downslope warming west of the mountains.  Depending on the track of the surface low--which major models do not have pegged, by the way, with the European going down into Alabama, the GFS in Tennessee, and the NAM in Kentucky--winds will be more or less out of the east in the WV mountains.  Air descending the western slopes to higher pressure levels will warm somewhat.  Both NAM and GFS bring surface temperatures in the lower elevations to about 33 F during the day Friday, potentially knocking down accumulations.  Good news for snow lovers is that it's brutally cold across WV right now.  Most areas brought to the melting point by downsloping on Friday would be reaching that point for the first time all week.  The ground will still be quite cold.

Another way for the snowstorm to flop is for a large part of the precip to fall as freezing rain and/or sleet.

Refresher on the difference between freezing rain and sleet, courtesy NWS

NAM and other SREF members are strongly suggesting a short period of moderate to heavy freezing rain in western WV sometime early Friday.  Accurately predicting precip type requires nailing down the vertical profile of temperature in the atmosphere.  One degree in a given layer can be the difference between a crippling snowfall and an inch of sleet.  So at this range, with the wave still offshore, it's a crapshoot.  The point is that if a lot of the precip falls as freezing rain and/or sleet, snow totals will be minimized.  Also know that significant ice accumulation from freezing rain can lead to power outages, so prepare for that possibility.