Friday, December 22, 2006

It Came Upon a Midnight Drear


Showers, cool. As the low which brought all that snow to Denver gradually spins down over the Great Lakes, convergence of Atlantic and Gulf moisture to the east is putting a damper on holiday cheer along much of the East Coast. Here in the Washington metro area, persistent light rain showers had put a mere 0.04" of water into the official measuring bucket by early afternoon, although that total has now slightly more than doubled. This month has just today been mathematically eliminated from breaking the record for driest December (0.19" in 1889), although only by a few hundredths of an inch so far.

Temperatures have barely budged all day, staying in the range of 45-48° for the last 24 hours. This Seattle-like pattern will be slow to clear out as we head into the holiday weekend.

Surface weather map and satellite picture at 1m today from HPC/NCEP/NWS

Tonight and Tomorrow

Showers continuing, cool. Showers, fog, and possibly some periods of heavier rain will continue through this evening and overnight. Temperatures will remain within a couple of degrees of where they are now, in the upper 40s. Conditions will start to dry out by the middle of the day tomorrow. If enough sun breaks out by early afternoon, highs could reach 60°, although the models are being somewhat optimistic about the timing on this, IMHO.

For the outlook beyond the weekend with Larson's Long-Range, scroll down to Josh's post below.


Andrew's Sunday Undercast on why climate change and broadcast meteorology don't seem to mix was picked up by the USA Today Weather Guys on Wednesday and by the Weather Channel blog yesterday. Both of them had some very thoughtful responses to the issues raised; I think Dr. Cullen's were especially insightful. WeatherTalkers, are you listening?

One thing I noticed about the posts at USA Today and TWC was the fact that, despite being national in scope, they each had only 1 comment. The one at USA Today was especially bogus. We are fortunate here at to have such a literate, well-informed, and enthusiastic audience. Please continue to share your input with us in the future (but be prepared to be challenged if you don't back up your assertions with facts).

Programming note: PM Update will be on "standby mode" next week. To steal a phrase from Comedy Central, however, whenever weather breaks, we'll fix it, posting as news warrants. We look forward to sharing with you the wonderfully wild and wacky world of Washington winter weather when our regular schedule resumes after New Year's. In the meantime, we send best wishes to you and your families for a happy, healthy holiday.

Thursday, December 21, 2006

Happy Solstice!


Cloudy, cool. Winter solstice is at 7:22pm tonight. A few peeks of sun and a southerly breeze were no match for a mid-level overcast and a few minor sprinkles of rain on one of the shortest days of the year in the Washington metro area. The temperature in most places stayed below 50°; the highs were 46° at National, 47° at Dulles, but 53° at BWI. Clouds will become thicker and showers will develop through the day tomorrow.

Tonight and Tomorrow

Showers developing, cool. Tonight will be overcast with a 40% chance of showers by dawn; lows will be in the low 40s in town, a couple of degrees cooler in the 'burbs. Tomorrow will be cloudy with showers likely, especially in the afternoon and earlier west of the mountains, with highs in the upper 40s.

For the outlook through the holiday weekend and beyond with Larson's Long-Range, scroll down to Josh's post below.


If you've been with us since last year (if so, thanks; if not, welcome!), you may recall we did some fun-with-numbers analysis of the relationship between December and January in Washington. Considering the amount of wailing and gnashing of teeth going on lately in the Comments section about the End of Winter As We Know It, this is probably a good time to take a second look at the data. The gist of the results is that, despite any amount of wishcasting, guessing, golden childhood memories, El Niño, NAO, or EIEIO, snow in Washington is enough of a random event that there is almost no connection whatsoever between the amount of snow in December and the amount in January. Anyone who tells you differently should be closely examined for controlled substances. In fact, the nearly microscopic amount of correlation (¼%) which does exist is actually slightly negative.

Since this December is well on its way to the "bust" category for snowfall, it's relevant to look more closely at the data points huddled along the y-axis in the original chart. The January snowfall for the 30 winters with December snowfall of 0.1" or less is shown in the chart above. Included in that set are 2 Januaries with over 20" each. The average amount of 5.6" is not very far from the January average of 6.6" for the entire period of record.

Although Mr. GW may have his greasy carbon-bloated thumb on the scale over at Momma Nature's Weather Grill and Deli, reports of winter's demise are certainly premature. (Before you fire up the political flamethrowers, please note that "GW" refers to "global warming", not a certain person's initials, but you knew that anyway, didn't you? ) chart from NWS data, photo © Kevin Ambrose

Clarification: In the interest of full disclosure, we should point out that a site visitor noted that the Union of Concerned Scientists climate projection map posted yesterday was based only on summer heat index. A projection based on the entire year would show a smaller geographic change.

Wednesday, December 20, 2006

Snow Crash


Sunny, cool. There was a rare sight for the current season in this part of MoCo this morning, a hard frost which persisted in north-facing areas until close to noon. Following the cold lows, a high layer of broken clouds defied the southerly wind direction to keep temperatures a couple of degrees cooler than yesterday. Highs were 48° at National and Dulles, one degree higher at BWI.

Clouds will be increasing as the blizzard walloping the Front Range of the Rockies heads toward the Great Lakes. As noted in Jason's post below, the SLCB isn't dead, it's just sleeping.

Tonight and Tomorrow

Increasing clouds, cool. Clouds will increase toward morning as lows tonight reach the mid 30s downtown and closer to 30° in the burbclaves. Tomorrow will be mostly cloudy with highs near 51°.

For the outlook through the rest of the week and into the holiday weekend, scroll down to Jason's post below.


The WaPo Washington plant climate article cited in Jason's earlier post is consistent with a study, "Climate Change in the U.S. Northeast", published a couple of months ago by the Union of Concerned Scientists. Depending on the level of greenhouse gas emissions, Massachusetts could be passing what used to be DC climatologically by mid-century on its way to the former South Carolina.

Accompanying the plant article on carbon-based page A1 is an article about the lack of snow so far this season in Europe as well. In Moscow, where 5 daily temperature records have already been set this month, street cleaners have put aside their ice axes and are reduced to picking up cigarette butts. Britain's Met Office reports that 2006 may turn out to be the warmest since temperature records began in England almost 350 years ago. A climatologist at the Central Institute for Meteorology and Geodynamics in Vienna (the other one) says, "We are currently experiencing the warmest period in the Alpine region in 1,300 years." An EU climate study has found that the current warming already exceeds warming periods in the 10th and 12th centuries.

Meanwhile, snow fans in the Rockies are happy, at least. A blizzard has shut down the United Airlines Denver hub as well as Colorado's 3 interstate highways, I-70, I-25, and I-76. There was a 20-car wreck on I-25 near Colorado Springs; at least 5 were injured. I-80 was also closed from Cheyenne, WY, to Ogallala, NE. Snow totals early this afternoon ranged up to 15" at Telluride, CO. (SUV drivers, please check out the photo in the link above before you try any stunts on the Beltway this winter.)

Tuesday, December 19, 2006

Why Ask Why?


Sunny, cool. In a more average December, it would be considered a thaw, but the low 50s in the Washington metro area this afternoon feel cold compared to the balmy records yesterday. Highs were 52° at National, 51° at Dulles and BWI. The relatively mild and dry conditions are likely to continue for a couple more days.

Tonight and Tomorrow

Clear, cool. Under clear skies and light winds, lows tonight will be near 34° in the city to the mid and upper 20s in cooler 'burbland. Tomorrow will be much like today, but with less breeze and highs again near 50°.

For the outlook through the rest of the week and into the holiday weekend, scroll down to Jason's post below.

ISO Snow

"Why ask why, when all that's true
The sky is blue, blue for no reason"

Bonnie Raitt, Blue For No Reason, from Fundamental

The snow lovers keep asking why, but the facts on the ground are that there is very little snow around so far this season. It may be no consolation, but they should be aware that they are not alone in being frustrated. The national plot of major reporting stations shows virtually zilch, nada, bupkis throughout the continental U.S. A more comprehensive view derived from satellite data is a little more interesting, but still limited to the western mountains and fringe northern border areas.

Until patterns are more favorable, you're going to have to be satisfied with virtual snow. The current (January/February) issue of American Scientist has an article, "The Formation of Snow Crystals", by the "Snowflake Man", Prof. Kenneth G. Libbrecht, professor of physics and chairman of the Physics Department at Caltech and author of "The Snowflake". The article itself is limited to subscribers, but there are several interesting links, including some animated computer simulations of snowflake growth. Libbrecht's work is also featured in today's WaPo KidsPost, online and carbon-based edition.

Snow crystal images from American Scientist

Monday, December 18, 2006

May in December; Records Fall


Mostly sunny, record warmth. A high temperature of 73° would be right at home on May 8, climatologically speaking, but that was the record-breaking reading at National Airport at 2pm today, a week before Christmas. Dulles blasted through its old record of 69° from 1984 with 76° at the same hour. BWI and Charlottesville also broke records set in 1984. Following a cold frontal passage, temperatures will return to more seasonable levels in the next couple of days, but the air behind the front is of Pacific origin, so the cold will not be particularly intense.

Temperature chart at 2pm today from Unisys shows 70s well into the Mid Atlantic region, while freezing temperatures are mainly confined to Canada.

Tonight and Tomorrow

Partly cloudy, cool. Under variable cloudiness tonight, lows will be from the low 40s in the city to the upper 30 in the 'burbs. Tomorrow will be mostly sunny and much cooler, with highs near 51°.

For the outlook through the rest of the week and into the holiday weekend, scroll down to Jason's post below.

Tropical Topics

A post-season review by the National Hurricane Center has identified a 10th tropical storm of the season. The unnamed storm developed on July 17 about 200 miles southeast of Nantucket and remained offshore, weakening before it crossed southeastern Newfoundland.

Seasonal Outlook

Latest seasonal forecast: Click here.

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