Thursday, March 15, 2007

Wintry Storm Developing
Heavy rain, some snow to follow temperature drop

*Flood Watch in Effect Friday Morning Through Friday Evening*
*Winter Storm Watch in Effect (N&W) Friday Morning Through Friday Evening*


Showers, breezy, turning colder. After reaching the low and mid 70s earlier, temperatures have dropped sharply in the Washington metro area with increasing northerly breezes. As the cold air is reinforced tonight, highs tomorrow will be 30° or more colder than they were today.

In the meantime, an ample supply of moisture which brought flooding rains to the Gulf Coast will feed into a developing low pressure area in the lower Mississippi Valley. As the low strengthens along the Atlantic Coast, heavy precipitation will affect the Mid Atlantic region tomorrow. Although this is likely to be mostly rain from DC south and east, a large pool of Arctic air will be anchored over eastern Canada, in a perfect position to provide frozen precipitation to the north and west, especially at higher elevations. In the immediate metro area, accumulations, if any, are likely to be minimal.

Tonight and Tomorrow

Much colder, heavy rain and some snow developing. Showers this evening will diminish somewhat as the main rainfall area develops to the south. Temperatures will continue to fall, reaching the mid and upper 30s by morning. Steadier precipitation beginning as rain by the early morning hours will continue, heavy at times, through most of the day tomorrow with temperatures steady or dropping through the mid 30s.

Although there is likely to be heavy snow in the mountains and accumulating snow in Frederick and Loudoun counties, there is a great deal of uncertainty for areas inside and near the Beltway because of uncertain temperature, both near the surface and higher up in the atmosphere. Based on the latest data, here are Team's most likely scenarios for tomorrow in the immediate metro area:

Scenario 1: Mostly rain, possibly mixing with and changing to snow. No accumulation.
Scenario 2: Rain, mixing with and changing to sleet, changing to snow late in the afternoon. Slushy accumulation of 1" or so on grassy areas.
Scenario 3: Rain changing to sleet to snow from west to east late morning to early afternoon. Snow, heavy at times, through the evening. Possibly messy rush hour. Accumulation of several inches possible, mostly on grassy areas except during periods of heavy precipitation, 6"+ Loudoun/Frederick Co.

The most likely scenario at this time is #2. We will continue to monitor the situation as it develops and update with an accumulation map or probability chart if necessary later tonight.

No comments:

Seasonal Outlook

Latest seasonal forecast: Click here.

Latest 3-month temperature outlook from Climate Prediction Center/NWS/NOAA.