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.

Wednesday, March 14, 2007

Spring Continues, but Winter Waits in the Wings


Partly sunny, very warm. A retreat of the jet stream northward into Canada has allowed early spring warmth to flood most of the country today, with freezing temperatures limited to a tiny sliver of northern Minnesota and North Dakota. Readings in the 60s reached into much of New England, and the Mid Atlantic region saw many low 80s. In the metro area, Dulles was 81° by 2pm, but the local readings were short of the upper 80s in the great March heat wave of 1990, during which Dulles set 6 consecutive daily records, including its all-time March record of 89° on the 12th.

A strong cold front working its way southward over the next couple of days will bring more wintry conditions back by the weekend.

Temperature chart at 2pm today from Unisys

Tonight and Tomorrow

Mostly cloudy, warm, chance of showers. Skies will remain mostly cloudy tonight with only a slight chance of showers and lows in the mid 50s (near or above the average highs for this time of year). Tomorrow will be mostly cloudy with a 70% chance of showers or thunderstorms in the afternoon and evening, highs 73-76°.

For the outlook through the rest of the week and into the weekend, scroll down to Jason's post below.

Mediaorology: DC destruction

It seems to have flown in below the radar screen, but Sunday's WaPo previewed the latest installment of The Weather Channel's disaster mockumentary, "It Could Happen Tomorrow". In "It", an imagined F-4 tornado rampages through Spin City, going right up the mall at 5pm on a Friday, "through the Washington Monument, between the museums and smack into the Capitol dome!" (There's no word on the fate of K Street.) In the tradition of the series, it uses a nearby event, the La Plata tornado of 2002, as a model for the DC destruction. The show, which premiered Sunday night, will be repeated soon and often in true TWC fashion. Look for it at 9:30pm Friday and 12:30am and 2:30am Saturday morning.

Graphic from The Weather Channel

Tuesday, March 13, 2007

January Rerun: That 70s Show


Sunny, warm. The official temperature was limited by a southerly river breeze, but nearly all reporting locations in the Washington metro area were well into the 70s for the first time since early January this afternoon under mostly sunny skies. On the southern fringes of the region, Fredericksburg was 81° at 4pm. Warm temperatures will continue tomorrow with some showers possible, but colder conditions will return by the weekend.

Tonight and Tomorrow

Increasing clouds, warm, chance of showers. Tonight will be partly cloudy with lows in the upper 40s to near 50°. Clouds will increase tomorrow with a 30% chance of scattered showers or possibly thunderstorms in the afternoon and highs in the mid 70s.

For the outlook through the rest of the week, scroll down to Dan's post below.

Disaster Preparedness

Today is Tornado Preparedness Day in Virginia. The Emergency Alert System was activated statewide at 9:45am, and schools and businesses carried out tornado drills with over 70,000 registered participants. Information on preparing for and responding to tornadoes is available on the state's Department of Emergency Management web site.

Seasonal Outlook

Latest seasonal forecast: Click here.

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