Fairly Fine Friday Saturday, Sunday: Snowy/Sleety/Soggy/Sloppy?

Now

Drizzle, cold. What had been expected to be a cold rain today has amounted to mostly an annoying light to moderate drizzle in the Washington metro area. By 4:00, National and Dulles had collected a mere 0.02" each, while the jackpot winner BWI had 0.04". Radar shows the bulk of the precipitation from this system from the Mason-Dixon line north and east, with moderate to heavy snow expected across portions of interior southern New York and New England.

The cold part of the forecast has materialized, however, as yesterday's midnight low of 47° is turning into today's high; temperatures are now generally in the upper 30s through the immediate area. After a drier and milder day tomorrow, a strong storm system will affect the Mid Atlantic region over the weekend.

Tonight and Tomorrow

Clearing, chilly. After any residual drizzle or light showers this evening, tonight's lows will be from the mid 30s downtown to the lows 30s in the 'burbosphere under decreasing clouds. Tomorrow will be mostly sunny and milder with highs 51-54°

Scroll down for Josh's outlook through the weekend and into next week.

Weekend Storm Outlook

The answer to the sub-headline's question is, "All of the above, the combination depending on your location and elevation." The models continue to paint a picture of a very vigorous storm emerging out of the Southern Plains on Saturday and bringing a wintry mix to the Mid Atlantic area by Saturday night and into Sunday. Although the latest runs from this morning and early this afternoon show some warming over the DC area, they also show a tendency for a strong secondary low to develop off the coast, which would keep more cold air in place. The complex dynamics of this interaction between the atmosphere at multiple levels and the land/ocean surface are not very well represented even by today's highest resolution models, so there is still plenty of room for variability in the final mix.

At this point, the best that can be said of frozen precipitation forecasts for this system is, "At least some of them will be wrong."

See Josh's Snow Lover's Crystal Ball below for more details on possible scenarios.

Historical Note

It might be just nostalgia kicking in, but the predicted evolution of this system reminds the Updater in some ways of his first experience with Washington snow, 50 years ago this month. The storm of Dec. 4, 1957 brought 11.1" of snow from a strong secondary development off the coast as the main system stalled over the upper Ohio Valley. That is still the second highest daily total ever for the month of December, but the temperature stayed at or above freezing; the daily high and low were 33° and 32°. The high 2 days before? 58°. That storm had a little more northerly course, however, and there was a very strong low over northern Quebec and Labrador.

Here's the forecast for DC and vicinity made the morning of Dec. 4, 1957:
"Today . . . wet snow and some rain ending this morning, clearing and windy this afternoon, highest 40°."

Weather map at 1am Dec. 4, 1957, from NOAA Library.

Cold Rain Gonna Fall Whither Wintry Weekend?

* Winter Weather Advisory in effect 3am to noon for northern and western areas *

Now

Mostly cloudy, damp, milder. Yesterday's high of 51° at midnight was enough to keep the temperature forecast from being a complete bust, but only technically, after the raw 40s in the afternoon. Today is somewhat milder, with afternoon readings mainly in the low and mid 50s, although by noon, both National and Dulles had reached the low 60s. Earlier mist and haze have given way to just mostly overcast skies.

Cooler and drier conditions are on tap for this evening while a storm system brings precipitation into the area from the southwest tomorrow. Temperatures are likely to be cold enough for the threat of frozen precipitation from about the Mason-Dixon line northward during the day, and closer to the metro area if precipitation begins earlier. A Winter Weather Advisory is in effect for the northern and western suburbs from 3am tonight to noon tomorrow for the possibility of sleet or freezing rain. Meanwhile, yet another storm system will be approaching the area over the weekend.

Tonight and Tomorrow

Cooler, rain likely. Lows tonight will be 36-41° under cloudy skies. Tomorrow will be mostly cloudy with a cold rain likely (80% chance) developing from southwest to northeast by late morning, possibly beginning as sleet or freezing rain in the northern and western areas and highs 41-45°.

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

Weekend Storm Outlook

"You might have even seen an accumulation map on the Internet. I think that's nuts at this point." (Howard B on WUSA-TV 9 news at noon today). Bravo, Mr. B! Speculation on the specifics of the storm expected to develop this weekend is just that at midweek: speculation. Nevertheless, the model gnomes in the basement of Momma Nature's Weather Grill are bound and determined to cook up a wintry treat (or trick, depending on your point of view) for the Mid Atlantic region from Saturday into Sunday.

The main U.S. model run this morning continues the trend of putting the DC area in the traditional transition zone between frozen and liquid precipitation. Even though there is a respectable pool of cold air anchored over eastern Canada and New England in the model forecast, temperatures in the immediate DC area would favor mostly rain. The models do have a tendency to underestimate the ability of cold air to persist near the surface in this type of situation, however, so it definitely bears continued watching.

The storm is just now coming into the sights of the shorter-range model known as the NAM, which runs out to 84 hr. (1am Sunday morning). The run from this afternoon's data was being output as this was written. It shows a much less vigorous development, but temperatures cold enough to favor frozen precipitation.

See Dan's Snow Lover's Crystal Ball below for more details on possible scenarios.

Conference Report

The RealClimate blog is reporting near real-time from the Fall Meeting of the American Geophysical Union (AGU) currently underway in San Francisco. The latest post a few hours ago covers the extension of the Antarctic ice core CO₂ record back to 800,000 years ago. As noted on Monday, the lecture "Abrupt Climate Change and Our Future" is available via webcast at 9:15pm Washington time tonight.

DC: Dreary, Chilly

Now

Cloudy, damp, cool. While temperatures in the Washington metro area moderated somewhat from yesterday's damp chill, within about 100 miles, spring-like conditions prevailed from central Virginia southward. Daily temperature records were set at Lynchburg, Roanoke, Blacksburg, Richmond, Norfolk, and Wallops Island.

Temperatures in the low and mid 50s were accompanied by dewpoints in the mid and upper 40s, but despite the humidity, mist and haze were much more prevalent than rain showers, which were mainly light. Highs were: National 54°, Dulles 48°, BWI 47°.

Clouds and humidity will persist into tomorrow with at least a chance of some showers. The models frequently underestimate the tendency of this type of cold air wedge to hang on in the area, but some warmer air is likely to make it this far northward in the next couple of days before everything gets swept eastward toward the end of the week.

Real-time Mesoscale Analysis (RTMA) from NWS/NCEP at noon today shows a 40° temperature range in about 100 miles from near DC to central Virginia.

Tonight and Tomorrow

Mostly cloudy, chance of showers, possibly milder. There's a 30% chance of light showers tonight with lows 41-45°. Some patchy fog is possible in the early morning hours. Tomorrow will be mostly cloudy with a 30% chance of showers, but some sun is possible, especially in the afternoon. Highs will be anywhere from 52-61°, depending on how much of the warm air can move northward.

Scroll down for Jason's outlook through the rest of the week and a weekend peek.

Tropical Topics

The National Hurricane Center issued an updated Special Tropical Disturbance Statement at 11 this morning on the low pressure area about 100 miles east of Puerto Rico. Although a tropical or subtropical cyclone could still form in the next day or so, upper level winds are now expected to become less favorable for development. Nevertheless, near gale-force winds and heavy rains are expected for Puerto Rico, the Virgin Islands, and Hispaniola.

Conference Report

The Fall Meeting of the American Geophysical Union (AGU) got underway today in San Francisco. Over 15,000 geophysicists from all over the world are expected to attend sessions in all disciplines of earth and space science. Several major lectures are available as live webcasts, including "Abrupt Climate Change and Our Future" at 9:15pm Washington time on Wednesday.

Suddenly Snowy

Now

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.

SchoolCast:

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 CapitalWeather.com 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.

Flakes Fly or Schoolkids Cry?

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

Now

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).

Mediarology

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.

Wintry Wind Whips Washington Some Slight Snow Seen Soon?

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

Now

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 . . ."