Christmas Storm Shaping Up

Wednesday has turned out to be a beautiful day. Despite the cold air and snow on the ground, the sunshine has made for pleasant conditions.

Afternoon visible satellite imagery shows that the snow from last weekend still covers the area.

A new storm is developing, just in time for Christmas.

A wider satellite view shows the storm in the Plains. Forecast models indicate that the storm center will stay well to the west of the Atlantic coast.

Moisture from the storm will be pushed eastward though and make it to the Atlantic coast by Christmas day. This moisture will be accompanied by an influx of warmer air. The complicating factor is that cold air will be in place at the surface when all of this starts to happen on Friday morning. This cold surface air will be a little slow to move out because it will be held in place by high pressure and resultant easterly winds as well as the chilling effect of the snow cover.

The computer model above shows predicted conditions in the mid levels of the atmosphere Friday morning. There will be plenty of moisture coming up the coast and the  0 degree celsius line (freezing line) west of Baltimore. The moisture will be rain at the mid levels but at it falls into that colder surface layer of air it is expected to result in freezing rain.

The surface forecast map for Friday shows the storm to the west and the surface high pressure area with its’ cold air reaching into the Mid Atlantic region from New England.

At some point on Friday the shallow layer of cold air will be pushed out of the area and the freezing rain will become just rain. The problem is the length of time that the transition will take. A best early guess is some time by early afternoon but until then freezing rain will likely cause some icy conditions.

The map above indicates that the rainfall amounts could be substantial and when combined with melting snow, some flooding may result.

The upshot is that what may start as a white Christmas will devolve into something slippery and a bit more dismal. It looks like we’ll just have to make the best of it.

Be watching for updates as Christmas draws closer.

John Collins

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