Another week, another cold air wedge, and another cold snap
For those folks patiently – or otherwise – awaiting the arrival of spring weather I’m afraid you’ll have to postpone your expectations for a while. As I mentioned in yesterday’s post today’s frozen precipitation is due to “overrunning” created by the Mid-Atlantic’s frequent – and unwanted – visitor known as cold air damming. Cool and dense surface air slides south along the coastal plain and Piedmont via northeasterly winds, channeled farther southward by the mountains. The lighter warm air being pumped northward ahead of the approaching cold front can’t push this dense wedge out of the way so it slides up and over the cold surface air and creates frozen precipitation (snow and sleet) over us. This cold air wedge is clearly seen in this surface forecast graphic:
The white arrow I’ve added shows the cold surface wedge pushing down into even northern Georgia while Kentucky and Tennessee are both much warmer than we are. In fact those states plus Mississippi and Alabama are expecting severe weather today while we deal with cold air and a snow/sleet combination. This wedge won’t go away until the cold front itself bulldozes it out of here tonight.
Meanwhile we can expect some light precipitation the rest of today (Monday) that will gradually turn over to all rain and then we could have some brief heavy showers when the front pushes through tonight. The high temperature will only creep into the upper 30s (F) today under the low overcast and easterly winds. Tomorrow the rain will clear out by mid-morning and the sun should reappear by noon. The “downsloping effect” of tomorrow’s brisk west wind will help temperatures climb into the low 60s but that warmth will be short-lived as the cold Canadian air behind the front suppresses high temperatures the rest of this week to the upper 40s and low 50s, a good 8-10 degrees below normal.
This cold snap will likely continue for the rest of March with perhaps a day or two of warmer conditions sprinkled in here and there. The long range weather indicators point to this cold pattern sticking around for a while as shown in this forecast graphic of the Arctic Oscillation (AO):
As you can see this parameter is tanking at present, showing a more deeply negative value than we have seen all winter. Although there are other such parameters that work in concert with (or against) the AO a very negative value as seen above often means much colder than average weather ahead for the East Coast of the U.S. That is what we will likely experience over the next couple of weeks. We aren’t done with winter yet!