Walk Like a Penguin

Dew points are currently sitting in the mid teens across the Washington Area setting up a textbook Cold Air Damming (CAD) situation. As precipitation begins falling through the dry mid levels of the atmosphere, temperatures at the surface will drop into the middle 20s and hold steady through the event allowing for all precipitation to freeze on contact.

Ice accretion between a tenth and a quarter of an inch will accumulate on trees, power lines and roadways causing treacherous travel conditions. The 100 car pile up in Dallas-Ft. Worth yesterday was a result from only a tenth of an inch of ice.  

Winter Storm Warnings or Ice Storm Warnings are likely along and east of Interstate 95 with a Freezing Rain Advisory likely for locations further north and west.

The image below is from the latest North American Model (NAM) showing sleet (orange) and freezing rain (pink) impacting the DC region beginning Saturday morning and wrapping up by noon on Sunday.

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How Much Snow Do I Think Will Accumulate?

The “prolonged” — ‘storm’ being advertised (if you can call it that) from Wednesday evening through Friday morning is a classic over-running event.  Over running occurs where warm air glides on top of cooler air at the surface causing condensation and precipitation. It is a weather scenario that typically ends up being a snooze fest of intermittent light snow, not a heavy snow that accumulates quickly. Sleet may mix in at times along and south of Interstate 66 and then we will likely have prolonged lulls in activity during the day on Thursday and then again on Friday morning when the heavier moisture looks to escape south of DC.

Every model I am looking at has the textbook look of a bust for DC. Temperatures look to be marginal at best cutting down what is already looking like pathetic SLR (snow liquid ratios).

The system I am more interested in arrives next Tuesday which will be coming from the south with ample moisture.


Tuesday Review of the Forecast Models

The latest GFS deterministic model (image below, courtesy WxBell)  shows snow developing Wednesday evening and continuing through Friday morning.

The next image is the GFS ensemble blend showing potential snowfall accumulations Wednesday through Friday.

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