Friday, December 21, 2007

DC: Dry Christmas?


Cloudy, seasonably cool. Despite the impressiveness of west-of-the mountains radar echoes inspiring some model maligning in Comment-ville last night, the Washington metro area remains mostly cloudy, but dry, on this pre-holiday-weekend Friday. Temperatures have been very close to seasonable levels, in the low to mid 40s. Highs were: National 46°, Dulles 45°, BWI 43°.

A weak low-pressure area now off the Georgia/South Carolina coast will continue eastward, but easterly wind flow will keep clouds in over us as an area of rain approaches with a cold front from the west by the second half of the weekend.

Tonight and Tomorrow

Mostly cloudy, cool, some drizzle or showers. Lows tonight under mostly cloudy skies will be generally in the mid to upper 30s. Some drizzle or light rain is possible, along with patchy fog. Tomorrow will remain cloudy with some drizzle and a 40% chance of measurable showers. Highs will be 45-49°.

Scroll down for Camden's outlook through the rest of the weekend and into next week, including the vanishing chances for a white Christmas.

Christmas Climatology: Whitest and Wettest

Climatologically, there is only about a 10% chance of 1" or more of snow on the ground on Christmas in Washington. Since 1929, there have been only 8 such occurrences. The largest amount was 7" in 1966, with 5" and 4" in 1962 and 1963, respectively. That was the only time it happened in consecutive years. The most recent was 1989, with 2". The wettest was 1.41" of rain in 1945.

Blast From the Past: Meteorological Mystery

The winner of the virtual T-shirt in yesterday's Meteorological Mystery contest is Augusta Jim, who recognized that the low temperature can occur any time during the day, including right before midnight, so the Dec. 20 record low of 2° and the Dec. 21 record of 1° were in fact one event. You can read his explanation in yesterday's Comments section.

An Honorable Mention for creativity goes to Havoc.


The dcrtv blog is reporting today that meteorologist Steve Rudin, formerly of channels 9 and 5, was spotted on News Channel 8 this morning.

In other weather media news, dcrtv reports that news station WTOP's audio has replaced classical music as background on WJLA-7's Doug Hill Weather Now digital channel (Comcast 204), and WASH's adult contemporary sound is accompanying WUSA-9's Live Doppler 9000 HD (Comcast 203).

And, in case you missed it, the results are in for the "Battle Of The Local Media Hotties": Channel 4's Chuck Bell beat out Channel 7's Adam Caskey by 1 vote. If we had only known earlier that nerdiness was so hot!

Best wishes for a happy and healthy holiday to all of our site visitors and their families from Update Central.

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.

Wednesday, December 19, 2007

DC: Dry Clouds DeCreasing


Cloudy, cold. Following some very light sprinkles and flurries this morning, most of which did not reach the ground, persistent overcast has kept afternoon temperatures from varying more than a degree or so from yesterday's. Daily highs were: National 42°, Dulles 41°, BWI 41°.

More sun but similarly cool temperatures are likely tomorrow after a weak cold frontal passage, with the next precipitation probably not on tap until the weekend.

Tonight and Tomorrow

Decreasing clouds, cold. Clouds will decrease overnight with lows in the low to mid 30s in the city and the mid to upper 20s in the 'burbosphere. Tomorrow will be mostly sunny with highs in the mid 40s.

Scroll down for Dan's outlook through the rest of the week and into the weekend.

Climate Corner

NOAA's National Climatic Data Center issued its preliminary annual report on the climate of 2007 last week. It states that "2007 is on pace to become one of the 10 warmest years for the contiguous U.S., since national records began in 1895 . . ." and that
The global annual temperature for combined land and ocean surfaces for 2007 is expected to be near 58.0°F and would be the fifth warmest since records began in 1880. Some of the largest and most widespread warm anomalies occurred from eastern Europe to central Asia.
Closer to home, unofficial estimates show the 2007 Washington average through the first half of December of 58.9° to be in the top 10% of warmest years, tied with 1953, 1959, and 1999 for 12th place in 137 years of records. Before getting too anthropocentric about that statistic, however, it's important to note that DC's 61.4 square miles are only 0.0017% of the total area of the U.S., which in turn is a small fraction of Earth's overall land area. Total land area itself is only about 30% of the total planetary surface. Interestingly, however, DC's annual average is within about 1° of the worldwide average, making Washington in some strictly symbolic sense representative of the entire planet's temperature.

Tuesday, December 18, 2007

DC: December Chill, Dueling Climate


Sunny, cold. After reaching morning lows of 27° at National and 20° at Dulles, temperatures are again barely reaching the 40s in the Washington metro area this afternoon, in spite of light southerly breezes. The air remains dry, with dewpoints within a couple of degrees either side of 20°. Last year's record of 74° was clearly in no danger of being broken, with identical highs of 41° at National, Dulles, and BWI.

Some high clouds overrunning the cold high pressure area sliding out to the east have dimmed the weak December sunshine. More clouds will be rolling in tomorrow, but with only a slight chance of precipitation. chart from NWS data, photo © Kevin Ambrose

Tonight and Tomorrow

Increasing clouds, cold. Lows tonight under partly cloudy skies will be not as cold as last night, 30-34° in the city and 24-28° in 'burbistan. Tomorrow will be mostly cloudy with highs 43-48°.

Scroll down for Matt's outlook through the rest of the week and into the weekend.

Political Science: "Stalling in Bali"

The performance of the U.S. at the just-concluded U.N. climate conference in Bali gets some serious criticism in at least one major newspaper today. The Dot Earth blog at the NYTi had a conference review over the weekend.

Last night's PBS NewsHour featured dueling climate negotiators, past and present. Transcript, podcasts (real and mp3 formats) and streaming video are all available at the show's web site.

Monday, December 17, 2007

Wild, Winning Weekend Winds Winding Down


Sunny, windy, cold. After causing as many as 100,000 customers to lose power and aiding the Redskins' win last night at Giants Stadium, the winds from the weekend storm were gradually diminishing this afternoon. Some gusts were still as high as 30 mph, however, making the temperatures in the upper 30s to low 40s feel even colder, despite bright, sunny skies. By 5pm, National was down to 16 mph, gusting to 23, and Dulles was at 15 mph.

The air is also very dry with dewpoints in the mid teens. The afternoon highs were: National 41°, Dulles 39°, BWI 39°.

With high pressure now dominating virtually the entire country from coast to coast, we can expect several days of more tranquil weather before the next storm system develops later in the week.

Tonight and Tomorrow

Mostly clear, cold. Under clear skies and diminishing winds, lows tonight will be in the upper 20s downtown to the upper teens in the cooler 'burbosphere. Tomorrow will be sunny with a few afternoon clouds and not as cold, highs 44-47°.

Scroll down for Jason's outlook through the rest of the week.

Weekend Storm Review

Although they were a bit iffy on precipitation type, as they usually are in borderline situations, the models were quite accurate in their prediction as much as 7 days ahead that a "bombogenesis" (rapid low pressure area development) would occur along the Atlantic Coast this past weekend. The causes of bombogenesis are rather complex, but these storms gain much of their energy from strong temperature contrasts along the coast in the winter. Probably the most definitive study on the subject was published in 1986 by Prof. Sanders of MIT, who is generally credited with inventing the term.

The surface weather maps above from HPC/NCEP/NWS show that a 1008 mb secondary low near the Outer Banks at 11pm Saturday developed into a 969 mb "bomb" along the Maine coast 24 hours later. Snowfall amounts in northern Maine by early this afternoon ranged as high as 17.2" at the NWS office in Caribou, where the month-to-date total is now triple the long-term average.

Stu Ostro has an excellent illustrated commentary on the storm through Sunday afternoon at The Weather Channel blog.

Seasonal Outlook

Latest seasonal forecast: Click here.

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