Thursday, December 6, 2007

Suddenly Snowy


Sunny, cold. After clearing skies and the new snow cover allowed temperatures to drop to the low 20s in the city and the low teens in the outlying areas (13° at Dulles, only 4° above the daily record), brilliant sunshine has been able to push readings barely to the freezing mark this afternoon. The very cold highs, even for December, were: National 34°, Dulles 32°, BWI 32°. As we approach the end of the first week, the month is now over 5° below average.

Tonight and Tomorrow

Mostly clear, then increasing cloudiness, cold. Under mostly clear skies early tonight, becoming partly cloudy later, lows will range from the mid 20s downtown to the upper teens in the coolest 'burbosphere. Clouds will increase during the day tomorrow with highs 39-43° and a slight chance (20%) of rain in the afternoon.

Scroll down for Kevin's and Ian's picture gallery from the storm and Josh's outlook through the weekend and into next week.

Precipitation Picture

For once, temperature was not a significant factor in yesterday's snowfall around the DC area, but Maryland won the accumulation contest because of larger precipitation amounts generally north of the Potomac and west of I-95. The 24-hour liquid-equivalent precipitation map through this morning from the NWS Precipitation Analysis shows a bullseye of mostly quarter-inch to half-inch amounts (dark blue) from the overachieving "clipper" storm in central Maryland.

Snow Removal

If you're dissatisfied with your local jurisdiction's snow removal operations, check out why residents of another large North American city are upset over their city's budget-cutting action. (For the non-metric mavens, 8 cm. was just about the average snowfall amount in this area yesterday. )

La Niña Update

NOAA today released the latest La Niña update. It indicates a "a moderate-to-strong La Niña through February, followed by a gradual weakening thereafter." Implications for U.S. weather "include above-average precipitation in the Northern Rockies, the Pacific Northwest, the Ohio and Tennessee Valleys, and parts of the Great Lakes region. Below-average precipitation is expected across the South, particularly in the southwestern and southeastern states."

Storm Update: First Snow of the Season

* Snow Advisory in effect until 11pm tonight*

9:30pm update: Snow is diminishing to flurries across the area. Generally 2-4" of snow has fallen (about 4-4.5" on untreated surfaces where I live in NW DC with some higher amounts to the north and west), with accumulation on untreated roadways. To snow lover's delight, this storm over-performed as the scenario we described (25% probability of 2"+) highlighting the potential for the development of localized heavy bands materialized.


4pm update: The early afternoon weather map showed the main center of the clipper system located in southwestern Virginia, while a new center was beginning to develop off the Outer Banks. Radar indicates light to moderate snow from central Maryland southward through the District. Temperatures have risen a couple of degrees to freezing or above during the afternoon at most locations in the immediate metro area. After reaching 34° in the previous hour, National has now slipped back to 33° and Dulles is at 31°.

Some updated unofficial snow totals reported in the last hour: Cumberland 2.5", Hunt Valley 2.4", Baltimore City 1.5", Frederick 3.0", Columbia 2.3", Germantown 2.3", Clarksburg 1.5" (TV met, probably Howard B), Bowie 1.5", National 0.7", Vienna 2.5", Reston 2.1", Leesburg 2.0". (Note that the 1" reported for National in the Comments was actually rounded up, so technically the official amount is not yet 1".)

Light to possibly locally moderate snow will continue through the rest of the afternoon, tapering off this evening as the new low pressure area in the Atlantic develops and moves away to the northeast. At this point, the majority of the accumulation has already occurred in most places. The NWS is planning to let the Snow Advisory expire on schedule at 8pm.

Stay tuned to for any further updates.

1pm update: The fast-moving clipper system hit the Washington metro area right where it hurts this morning: in the middle of rush hour. The combination of temperatures just a little below freezing and the timing of the arrival of the first flakes (5:47 at Dulles, 6:23 at National, 7:32 at BWI) made for a very nasty trip for many commuters and caused some school systems to throw in the towel by closing early.

Although the snow intensity increased to heavy at National for a short time around 12:40 with visibility only a quarter of a mile, actual precipitation amounts so far are quite light: National didn't pick up its first 0.01" until 11:00, and the total so far is just 0.08" of water. With temperatures still at or slightly below freezing, however, some measurable snow has accumulated, especially on grassy and elevated surfaces. Unofficial observations shortly after noon included (some observations made earlier): Cumberland 2", Frederick 2.5", Columbia 1.1", Great Falls 0.9", Leesburg 1.4", Sterling 0.5".

Current radar shows the back edge of the current precipitation moving eastward from western Frederick Co. MD and Loudoun Co. VA. There's another batch of snow moving eastward from the Ohio Valley which should bring a resumption of light to possibly moderate snow in the area later this afternoon before it all tapers off this evening.

We'll be back by around 4:00 with a further update, earlier if conditions warrant.

Tuesday, December 4, 2007

Flakes Fly or Schoolkids Cry?

Next update: 10-10:30pm, with accumulation map, SchoolCast and frequently asked questions.


Mostly sunny, cold. Following some stray snow showers this morning, it's been a mostly sunny (but with some increasing high, thin clouds), breezy, and cold day in the Washington metro area. By early afternoon, temperatures at many locations were barely reaching 40°. Highs for the day were: National 42°, Dulles 39°, BWI 38°.

The next weather maker for the region is a weak "clipper" system just getting organized in the upper Midwest. The latest models this afternoon confirm that this system should move quickly southeastward, bringing with it the likelihood of some light snow tomorrow.

Tonight and Tomorrow

Increasing clouds and cold, then some light snow. Clouds will increase and winds decrease tonight with lows in the upper 20s to near 30° downtown and the low to mid 20s in the 'burbosphere. Some light snow or flurries could develop by dawn, especially to the west of the Blue Ridge. Intermittent light snow or flurries are likely tomorrow (70% chance) with most places in the immediate metro area seeing up to an inch on grassy areas. Some colder locations to the north and west could get as much as 2". Highs will be 34-37°.

For the outlook through the rest of the week, including the detailed Snow Lover's Crystal Ball and SchoolCast, scroll on down to Matt's post below.

Snow Crystals

While you're waiting for the flakes to arrive (or not) at your particular location, you can read about the physics of snow and ice crystals in this month's Physics Today Quick Study (free online to non-subscribers).


Today's Diane Rehm show on WAMU-FM featured "Politics of Global Warming", including the UN climate conference currently meeting in Bali and prospects for energy legislation in Congress. Guests were David Doniger, climate center policy director, NRDC; John Fialka, environment and energy reporter for "The Wall Street Journal," Washington bureau; and John Stowell, V.P. environmental policy, Duke Energy. Multiple flavors of streaming audio can be found at the usual joint, and a podcast is available on iTunes.

Monday, December 3, 2007

Wintry Wind Whips Washington
Some Slight Snow Seen Soon?

*Wind Advisory* in effect through 1am tonight. Significant risk of power outages.


Variable clouds, windy, cold. Gusty northwesterly winds following a strong cold frontal passage have knocked the temperatures down at least 10° this afternoon from a morning high of 53°. That makes the 43° at 5pm the low for the day so far. The humidity drop is even more dramatic, with dewpoints crashing from the mid 40s this morning to the upper teens now. Peak wind gusts reported include (in mph): BWI 47, Camp Springs 49, National 47, and Ft. Belvoir 51. Radio reports indicated that local utilities had experienced several thousand power outages by early this afternoon.

Strong winds will continue into tonight as the colder air sets the stage for a "clipper" system racing southeastward toward the region with some light snow possible for Wednesday.

Tonight and Tomorrow

Windy, colder. Gusty winds will continue through this evening, but will diminish somewhat by morning. Lows will be generally 28-34°. Mainly clear skies and northwesterly breezes tomorrow morning will give way to increasing clouds late in the day with highs 41-45°.

For the outlook through the rest of the week, including the revived Snow Lover's Crystal Ball, scroll on down to Jason's post below.

Trivia Notes

  • December 1 is the latest date in the season on which 1" or more of snow has never fallen in Washington, so Saturday's infinitesimal trace of frozen precipitation tied the record for the date.
  • Today's record of 1" is the second lowest for the month of December.
  • Today's sub-headline is a former Googlenope.

Making Hay While the Sun Shines

Want to pick winning investments? Studies have found that stock markets around the world tend to go up more on sunny days than cloudy ones.

Political Science

A local newspaper has an op-ed piece today, "A New Green Economics", by UN Secretary-General Ban Ki-moon, in connection with the opening of the international climate conference today in Bali.

As those negotiations get underway for a follow-on to the Kyoto climate agreement, the NYTi's Dot Earth blog notes that the newly-elected Prime Minister of Australia, as his first official act, has signed the Kyoto Protocol. Blog author Andrew Revkin notes that "leaves the United States and Liechstenstein as the only industrialized countries not bound by the pioneering, but troubled, pact . . ."

Seasonal Outlook

Latest seasonal forecast: Click here.

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