Sunday, December 21, 2014

Light Wintry Mix Possible Monday Morning

12/21/14 9pm
Setup: A wave of low pressure forming off the southeast coast will track up the eastern seaboard. Although the bulk of the precipitation associated with this will stay east of I-95, the western fringe may push as far west as the VA/WV line. At the same time, an area of high pressure retreating into eastern Canada will wedge just enough cold air into western VA for a period of sleet/snow/freezing rain Monday AM. Lack of much precip+ marginal cold air leans towards this not being a huge deal...but certainly worth mentioning. 
18z nam 10am Monday

Temperatures are already cooling down quite nicely this evening thanks to clear skies allowing radiational cooling to go to work.  We are generally in the upper 20s to low 30s, likely dropping a few more degrees as we progress through the night.
8pm Temperatures
These temperatures will certainly be cold enough to support a period of wintry mix during the early morning hours in the areas that see precipitation arrive early enough.  These chances improve the further south and east you go since moisture will be fighting dry air to the north and west. It might not make it to the northern Valley until mid to late morning when daytime heating will have then warmed the surface enough to support all rain.  

The National Weather Service in Sterling has issued freezing rain advisories for up to a glaze of freezing rain and the potential for a quick coating of sleet/snow.  You can see how this advisory is cutoff because of the uncertainty with timing I mentioned above.  If precipitation was to work in a few hours earlier, these would likely need to be expanded north...and vice versa if the drier air wins out and delays precipitation onset. 

Bottom Line:  It's always a tough call when you have meager moisture overrunning dry air at the surface in regards to timing and how much falls..  Not everyone is going to have issues in the morning...but I'd head to the car a little early in case you need to scrape your windshield.  Take it easy on the roads, especially if you have to head over the Blue Ridge mountains which always seem to be the problem spot for these type of events.

No comments:

Post a Comment