Winter storm will start Tuesday as snow

This morning's snow flurries and showers demonstrate that the weather pattern that has set up around us is capable of delivering some snow. And it will in the next two days.

But this is not our ideal snow-making scenario. Temperatures will slide past the freezing mark as the events unfold. Accumulations throughout this period will be small, and what starts as snow late on Tuesday will morph into freezing rain and finally rain by lunchtime on Wednesday.

But it will look enough like a real winter that the National Weather Service has issued a Winter Storm Watch for all of Maryland north and west of Baltimore and Washington, including their Arundel, PG and Montgomery county suburbs. The watch begins around 6 p.m. Tuesday and continues into the early evening on Wednesday. It calls for  the familiar, and always popular "wintry mix." 

Here's the official forecast for BWI. Here's how sees it.

More immediately today, light snow showers are expected to continue off and on as weak disturbances track along the jet stream track that is flowing west-to-east along the stalled boundary between cold air to our north, and warmer, wetter air to the south. Nobody expects any accumulation out if this early phase of the week's winter weather. We may even catch a few glimpses of sun and sky between the clouds.

The next of these little stormlets will barrel through later tonight, with more light snow after midnight. This one will be a bit stronger than today's, so we may get an inch - maybe two - on the ground during the day on Tuesday. The overnight low at BWI is forecast at 24 degrees. Tuesday's forecast high is 30 degrees

Late on Tuesday, and into Wednesday, the pace picks up a bit more, but so does the temperature. Forecasters think the next low to roll along the frontal boundary will track to our north and west, from West Virginia into southwestern Pennsylvania. A secondary low is likely to form off the Delmarva coast. That will draw more warm, wet air into the region from the south, raising temperatures aloft and - depending on how much cold air hangs on at the surface - changing our precip from snow to freezing rain and plain rain during the day on Wednesday. The forecast high for BWI is 34. Here's a clip from this morning's forecast discussion from Sterling:

"The exact details of of the timing and track of this system are not exactly certain at this time," the forecasters caution. "And that will play a significant role in [precipitation] type. The main threat appears to be snow and ice near the Mason Dixon Line, with snow and ice changing to rain near the Washington and Baltimore metropolitan areas into Central Virginia."

However it works out for us, the storms should move off the coast late on Wednesday, drawing colder air from the north in its wake. That could end the event with more snow showers. Thursday looks sunny, but temperatures will continue to run below seasonal norms, as they have since mid-month. The next cold front passes by on Friday, kicking up a coastal storm that forecaster don't believe will affect us.

Sunny but cold is the prescription for the weekend.

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