Update on Monday-Tuesday Winter Storm

The Global Forecast System (GFS) model has shifted slightly more east in its 12z run.  The Canadian model is also more eastward in track and weaker while the European forecast model is tracking the system right up the Appalachian chain.

Below is the latest European Operational model for snowfall accumulations before any change over to ice or rain: The snowfall ratios on this map are 1:10 but given how cold the air will be the ratios will probably be running much higher Sunday night and Monday (probably 1:15 or 1:20) so a general 2 to 5″ could fall in the immediate Metro Area before a change over to ice and possibly rain. 

ecmwf_tsnow_washdc_21

GFS Snow and Ice Accumulation Forecast: The first image shows potential snowfall accumulation before a change over to ice and rain.  Again a general 2 to 5″ of snow seems reasonable given the current model data (subject to change).

The second image shows ice accumulation from freezing rain (top right box).  Some locations in the western foothills of the Blue Ridge and Shenandoah Valley could pick up a quarter to a half an inch of ice if the GFS’s current colder/more eastward track verifies.

gfs_6hr_snow_acc_washdc_19

gfs_ptype_accum_washdc_19

Canadian Snowfall Forecast:  This model has continuously had a more eastward track but it is also known to have a cold bias, so I would discount the very bullish snowfall totals on it.

cmc_snow_acc_washdc_19

I will be looking to see if the 18z GFS continues to shift east, or if it shifts back west this evening. Also I will be watching the European forecast model to see if it shifts further east or if the model holds steady with its westward/warmer track for our area.

If the Euro is correct, we would be looking at some very heavy rain on Tuesday with temperatures rising into the lower to middle 50s! Models are notoriously bad at scouring out low-level surface cold air so this forecast is very tricky especially given the ongoing differences in track.  Hopefully some consensus will build tonight and tomorrow.

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