Friday, December 28, 2007

Raindrops Falling on Your Head


Cloudy, cool. Following sunny skies this morning, clouds have overspread the Washington metro region this afternoon ahead of a low pressure area developing in the Mid-Mississippi Valley. By mid afternoon, rain and showers on radar had reached as far as the southern Blue Ridge and most of West Virginia. At 4pm, Charlottesville reported light rain had just begun, with only a trace accumulated. The rain will move into the area this evening, generally from southwest to northeast.

Temperatures are on the mild side for this time of year, reaching the upper 40s in most places. The daily highs were: National 50°, Dulles 48°, BWI 47°.

Tonight and Tomorrow

Rain, mild. Rain, developing this evening, will continue overnight, with temperatures nearly steady in the low to mid 40s. Rain will end tomorrow morning, with decreasing clouds in the afternoon and highs 50-55°, but turning colder late in the day and at night.

Scroll down for Camden's outlook through the rest of the weekend and New Year's Day.


One of the things the atmosphere does for you is to keep raindrops falling on your head at times, but it also keeps other, nastier stuff from falling and killing you. Today's SciFri on NPR reported that NASA's Near Earth Object Program is tracking a 50-meter wide asteroid, discovered when it was near the Moon, which is on its way to a 25% chance of impacting Mars. The object, if it hits on Jan. 30, could produce quite a show. Since the atmosphere of Mars is less than 1% as dense the Earth's, an object of that size could do some significant damage, creating a crater about half a mile wide.

Mars image from NASA/JPL

Thursday, December 27, 2007

DC: Definitely Changeable


Mostly sunny, mild. While yesterday's coastal storm has pulled away off New England, mostly sunny skies across the Washington metro region have helped temperatures climb above the forecast range, to the mid and upper 50s in most places. On the southern fringe of the area, Culpeper and Fredericksburg broke the 60° mark.

The double-digit above average daily highs were: National 58°, Dulles 54°, BWI 54°. Going into the last few days of the year, the month overall is now running about 1.5° above the long-term average. This keeps 2007 on track for a 4-way tie as the 12th warmest year in Washington records.

As Josh has already noted, a pattern of fast upper-level westerlies will keep things unsettled heading on into the end of the year.

NWS Precipitation Analysis above for the 24 hours ending 7am this morning shows half inch or greater amounts (green) to the southeast of DC and progressively lighter amounts to the north and west. The lightest blue area covering most of Frederick and Loudoun Counties represents less than 0.1", and inside the Beltway was generally in the range 0.1-0.25".

Tonight and Tomorrow

Partly cloudy, cool, then chance of rain. Lows tonight under variably cloudy skies will range from the mid and upper 30s inside the Beltway to 28-32° in the outer 'burbosphere. Clouds will increase tomorrow afternoon with a 30% chance of rain by evening and highs 45-50°.

Scroll down for Josh's outlook through the weekend and into New Year's Day.

Wednesday, December 26, 2007

Seminar Series

The PowerPoint slides from Fred Singer's presentation to this month's DC MIT Club seminar series, "The Great Climate Change Debate", have been posted to the Club web site. Prof. Singer "is a leader among those who have emphasized natural factors over anthropogenic causes to explain global warming."

Next month's lecture is "The Findings and Forecasts of the Climate Change Scientists", by Prof. Ronald Prinn, Director of the Center for Global Change Science at MIT. Having had no takers so far, PM Update's previous offer to host any TV meteorologist at the seminar series still stands, provided seats remain available.

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.

Thursday, December 13, 2007

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


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.

Wednesday, December 12, 2007

Cold Rain Gonna Fall
Whither Wintry Weekend?

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


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.

Monday, December 10, 2007

DC: Dreary, Chilly


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.

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 . . ."

Thursday, November 29, 2007

November Prepares to Leave Town Cool and Dry


Clear, mild. After some morning cloudiness, clear skies ahead of an approaching cold front have been accompanied by southerly winds and temperatures a bit milder than expected. Readings were at least 60° in most parts of the Washington metro area this afternoon, with highs of 61° at National, 60° at Dulles, and 58° at BWI.

Meanwhile, the long-term dryness continues as we roll on toward closing out the month with just over 50% below average rainfall. The fall season (Sept-Nov) is about 12% below, and the year to date is 17% under average. The yearly total is now running over 10" below last year's wet pace. The next precipitation, from a storm system emerging out of the Southwest toward the Great Lakes, is likely this weekend.

Tonight and Tomorrow

Mostly clear, colder. Under clear skies tonight, lows will range from the low 30s in the city to the upper 20s in the 'burbosphere. Tomorrow will be sunny and colder with highs 46-50°.

For the outlook through the weekend and beyond, scroll on down to Josh's post below.

Winter Outlooks

In case you missed it,'s winter outlook is here, and NOAA's final winter forecast update is here.

As a reminder that the rest of the Northern Hemisphere has winter around this time also, Japan's JMA is predicting "mostly average to milder-than-average winter weather", and the UK Met Office expects the winter to be "warmer than average, particularly in northern Europe, but cooler than last year". Environment Canada also produces an extensive set of seasonal forecasts. The current forecast (Nov-Dec-Jan) calls for over a 50% chance of below-normal temperatures over most of the northern half of the country.

Wednesday, November 28, 2007

November Rollercoaster Continues


Clear, cool. Under mostly clear skies with some approaching high clouds from the southwest, temperatures are somewhat cooler this afternoon in the Washington metro area. Most locations remained in the upper 40s, with highs of 49° at National, 46° at Dulles, and 45° at BWI. The air is also very dry, with most dewpoints in the teens or lower 20s yielding relative humidities of around 30-35%.

Temperatures will rebound upward tomorrow before turning colder again toward the weekend. chart from NWS data, photo © Kevin Ambrose

Tonight and Tomorrow

Partly cloudy, milder. Clouds will increase overnight with lows in the upper 30s in the city to the low and mid 30s in the 'burbosphere. Mostly cloudy skies tomorrow morning will become mostly sunny in the afternoon with highs 55-59°.

For the outlook through the rest of the week and weekend, as well as the temporary obituary of the Snow Lover's Crystal Ball, scroll on down to Jason's post below.

Bucket O' Bookmarks

As a prolific generator and consumer of real-time data, meteorology is a perfect match for the World Wide Web. In this occasional feature, Update will share some of the weather-related sites we've found useful, interesting, or just plain fun over the last decade and a half. At last count, we had accumulated close to 1000 links in several dozen folders (24 pages of 12-point Times New Roman type).

One of the newest web destinations is the completely redesigned National Weather Association site, which debuted last month. The site is well-organized and, very much appreciated by a former performance analyst here in the cone of broadband silence, it's very snappy to load. (Verizon, can you hear me now?) Some of the highlighted features include the first 2 downloadable modules of an introductory weather course for pilots and the recently announced list of winners of the 2007 Sol Hirsch Education Fund Grants. Once again, despite our prodding, there were no winners from the DC/MD/VA area among the 10 award recipients. Perhaps if you K-12 teachers work on your applications while you're clicking on "Reload" for the Snow Lover's Crystal Ball to reappear, the National Capital region can be better represented next year?

If you have a favorite weather site (other than, of course!), let us know in the Comments.

Tuesday, November 27, 2007

Sunny, Seasonable Supplants Skimpy Showers


Sunny, breezy. Following a midnight high of 64°, temperatures have trended generally downward today with the help of the early-morning passage of a cold front, but by mid afternoon they were still near the seasonal average in the mid 50s. With the arrival of a reinforcing shot of cold air, readings should be a little cooler tomorrow.

Despite yesterday's gloominess, rainfall amounts through this morning in the immediate metro area were nearly all less than 0.25", but higher toward the north and west. (The middle shade of blue in most of the western suburbs represents 0.10-0.25", while the District itself and points east are generally less than 0.10".)

Precipitation chart through 7am this morning from NWS Precipitation Analysis

Tonight and Tomorrow

Mostly clear, cool. Breezes will diminish tonight under clear skies with lows ranging from the mid 30s in the city to the upper 20s and low 30s in the 'burbosphere. Tomorrow will be sunny and a little cooler, with highs 48-51°.

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

Blogospheric Climate

The NYTi's Andrew Revkin reported in his DotEarth blog yesterday on the controversy surrounding the linguistic license used by Dr. James Hansen in his choice of metaphors for describing the consequences of global warming. David Roberts also has some extended comments at Gristmill. Dr. Hansen was one of the first scientists to publicly raise the issue of the policy implications of climate change.

SciAm has just started a new online feature called "Clash", which explores the policy issues related to various scientific topics. The inaugural posting discusses the question, "What Will Climate Change Cost Us?", with economist Sir Nicholas Stern, author Bjorn Lomborg, and a lead IPCC author Gary Yohe.

Monday, November 26, 2007

Where's the Rain?


Showers, cool. This afternoon's local area forecast discussion was asking, "Where's the rain?", as a low pressure area moved northeastward through the Ohio Valley along with its associated complex warm fronts. Through mid day, metro area amounts were quite disappointing for the waning days of a month which so far had been nearly 50% below average. National picked up a mere 0.03" overnight, and Dulles had only a trace. By mid afternoon, however, showers had reached at least the western portion of the region, and Dulles had 0.14" in the hour ending at 4pm. There is still plenty of moisture around as a cold front extending southward from the low moves eastward, so showers and even some thunderstorms are likely through midnight tonight.

Surface weather map at 4pm today from IntelliWeather

Tonight and Tomorrow

Showers and mild, then clearing and cooler. Showers are likely through this evening and into tonight with chances decreasing to 20% by morning and lows 47-50°. Skies will clear by tomorrow afternoon with highs 55-59° and increasing northwesterly winds.

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

Tropical Topics

With the official Atlantic tropical season rapidly winding down, AccuWeather's Joe Bastardi was recently interviewed by the Sarasota Herald Tribune on the somewhat less than stellar results of his hurricane season forecast.

The Miami Herald's hurricane reporter Martin Merzer today reviews the Colorado State Gray/Klotzbach and NOAA tropical season forecasts and raises the interesting question of whether such forecasts (and, by implication, seasonal outlooks in general) do more harm than good by undermining confidence in short-term storm warnings.

Business Climate: Easy Being Green?

On a slow business news day, a local DC newspaper has a collection of articles on the attempts of Washington-area businesses to balance environmental challenges with opportunities for the pursuit of profit. Included are SunEdison and its CEO Thomas Rainwater (apparently his real name), Honest Tea, Marriott International, Tower Cos., and Trex. The Federal Diary covers the design of a new building for the National Renewable Energy Laboratory, and there is also a review of the recent Greater Washington Board of Trade conference "Green as a Competitive Advantage".

Seasonal Outlook

Latest seasonal forecast: Click here.

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