Thursday, December 20, 2007

DC: Developing Cloudiness


Sunny, seasonable. Despite light northwesterly breezes behind a weak cold front, bright sun has helped push temperatures to seasonable levels in the Washington metro area this afternoon. Highs were a little warmer than originally expected: National 49°, Dulles 46°, BWI 47°.

If you didn't get out and enjoy the sunshine today, you'll have to wait several days as more unsettled conditions develop into the weekend.

Tonight and Tomorrow

Increasing clouds, cool. Clouds will increase tonight with lows 32-35° in town ranging down to the upper 20s in the 'burbosphere. Tomorrow will be mostly cloudy with highs 42-47° and a 20% chance of light showers or drizzle developing, especially westward toward the Blue Ridge, as a storm system scoots by to our south.

Scroll down for Josh's outlook through the the weekend and into next week, including the prospects for a white Christmas.

Blast From the Past: Meteorological Mystery

As noted in "Today in Weather History" to the right, Dec. 20, 1942 was the beginning of a cold spell in which the modern Washington low temperature record was set for December, exceeded only by the -7° and -13° on Dec. 30 and 31, respectively, in 1880. The month as a whole went on to be about 5° below the long-term average, but it barely made it into the top 30 coldest Decembers, averaging 6.5° warmer than 1989, which is tied for second place. By comparison, the monthly low in 1989 was 5°.

An excerpt from the early-morning (1:30am) weather map for Dec. 20, 1942 is shown above. The temperature at Washington is 21° with light snow ahead of a low pressure area centered in the Tennessee Valley. Moderate snow extends back into the Midwest, with heavy snow at Chicago. Washington went on to receive 3.7" of snow for the day.

The Meteorological Mystery is: How could the reported low temperature for the day drop to 2°? The original map notes, "This map was not released until 7 days after above date." Was it a ruse to confuse the enemy in war time? Was it an "urban cold island" at then brand-new National Airport? Was it a conspiracy by the World-Wide Global Warming Gang? The first correct and complete explanation wins a T-shirt (IF we ever have any T-shirts!). Members of and professional meteorologists not eligible. The answer will appear in a future PM Update.

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Seasonal Outlook

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