The rain is past and a cold front will sweep out the chilly, damp, patchy-icy wedge overnight. Tuesday may seem kinda mild after Monday’s dank chill, despite the breeziness behind the front, as highs climb into the 50s with sunshine. Cold air gets reinforced by a cold front and clipper-like disturbance late Wednesday and Thursday, with some rain and snow showers also possible.
Somewhere along the way during our record warm March a year ago, when the air-conditioning units were being replaced at the Roanoke Times office with temperatures topping 80 and no ability to open the windows, I half-jokingly suggested that the next March would probably be unseasonably cold with chances of snow. Well …
We are on the cusp of an unusual period of cold late March weather that will at least add to the quirkiness of the 2012-13 winter (and early spring) and could become quite memorable or even historic, depending on just how cold it gets and whether we get a significant early spring snow. Today’s initiation of the European forecast model (12Z) shows some regions of green near Greenland and the North Pole, signifying unusually high atmospheric heights. These regions of high pressure are blocking the jet stream, forcing far a far south dip that will be developing, allowing Arctic air to sink all the way to the Gulf of Mexico. Arctic air in late March doesn’t produce the same effect as it would in January. There may not be any days of widespread below-freezing highs, but many days of highs in the 40s and lows in the 20s will run 15+ degrees below normal in much of Southwest Virginia. The Climate Prediction Center rarely hauls out the dark blue crayons for a 90 percent chance of below-normal temperatures, as it does in the 6-10-day period. With this blocking pattern in place, the cold air won’t be going anywhere fast, and will be reinforced a few times. A clear night with calm winds and snow cover could produce record lows in this setup. But will there be snow?
The blocking pattern also increases the chance that atmospheric energy will dive southeastward and trigger a large precipitation-making low-pressure system somewhere in the South and/or East. Forecast models are struggling a bit to determine which piece of energy at exactly what time may do this, and are varying dramatically on where precisely it could happen (Ohio to Florida!) and how the storm will evolve. But the generally developing idea is that this weekend or early next week could produce a large low somewhere in the South or East capable of spreading moisture into the unusually cold air. Things usually have to be a little extreme to produce a widespread snow event at our latitude in late March. It appears this pattern is extreme enough to support such a development … IF the pieces come into line. Hopefully there will be a little more clarity on what kind of system (or systems plural), and where and when it may develop, in a couple of days.
My general expectation is that our region probably will see some accumulating snow, maybe more than once, over the next 7-10 days. There is potential for a widespread winter storm affecting a large region including our area, but too much remains uncertain for me to hop on that train just yet.