Winter Again! Tired Yet? Sunday 3/16/14 - Monday Night 3/17/14 (Brent/Raleigh)

UPDATE Sunday 4:45pm: Model guidance still unclear about temperatures aloft overnight tonight. Dry slot is moving in as predicted W to E, so precipitation overnight should remain steady through about 8pm, and as the lifting mechanism weakens and air aloft dries out, expect precipitation to become scattered and drizzly. Some freezing drizzle may occur overnight from the Triangle N and NW, but at least in the immediate area should be of little consequence. The ground has been sufficiently warmed by the March sun and warm temperatures such that it actually gives off heat, thus cutting down or eliminating ice accrual near the surface. This warming does not rule out the possibility of slick overpasses.

Monday UPDATE: Precipitation should be light and becoming lighter throughout the day, with any freezing drizzle thawing out by midday. An upper trough axis moves over during the day and with this trough, rain may become more steady. Other than this, not much has changed for Monday from what I posted last night (below).

Monday Night UPDATE: According to NWS, models are coming in drier for Monday night's event. This would be fortunate as our temperature chances for seeing nuisance icing are more favorable Monday night into Tuesday morning.

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With most of VA and MD already under winter storm watches and warnings, things are once again looking like N Central NC will be on the southern fringe of yet another arctic airmass interacting with precipitation. We don't have much longer, folks. These storms at this time of year are already in the climatologically unfavorable category. This unfavorability makes them even harder to forecast than they are in January and February. Hopefully everyone is enjoying this warm weather sunny Saturday we are having. I will attempt to summarize this complex forecast below.

Sunday: An upper level trough will slowly evolve over the next couple of days just west of the Appalachians into TN, while Sunday a surface low pressure system moves toward the TN valley. A secondary low will develop off the Carolina coast Sunday night. A front will move N tomorrow as precipitation comes with it, spreading SW to NE. 1-1.25" of rain expected into the afternoon. Temperature forecasts are difficult. Temps will begin to drop as the day progresses and precipitation moves in.

Sunday night: Forecast becomes even more difficult as a secondary cold front pushes into NC from the N bringing with it air from Canadian high pressure. Latest models have trended colder with the airmass. The precipitation forecast becomes even more tricky as a "dry slot" (a large area of dry air which moves into a mesoscale low pressure system. See an example HERE ) may move in early Monday morning. A dry slot will cut down tremendously on precipitation amounts. The chance for freezing rain occurs during this timeframe.

Monday: Drying is expected. This is fortunate because if precipitation were heavy enough during this time, the wet bulb (the temperature that occurs when evaporational cooling has reached its full effect and an airmass is completely saturated) temperature would be below freezing, thus rendering all precipitation as sleet, freezing rain, and possibly snow. Since precipitation amounts are supposed to wane during this time, the temps may be allowed to rise some. Expect light rain and light wintry mix N of a line from Albemarle to Fuquay Varina to Wilson Monday, with all rain S of the line.

Monday Night: The greatest threat of nuisance weather comes Monday night. Wet bulbs will certainly be below freezing. With model disagreement on precipitation amounts during this time period, it is wise to hold off on making any call. If a winter weather advisory is to be needed, this will be the time in which it will be needed. I urge everyone to pay close attention to the weather forecasts over the next couple of days.

NWS Forecast for Sunday: