Friday, September 29, 2006

After the Fall


Breezy, chilly. After yesterday's strong cold frontal passage, temperatures in the Washington metro area struggled to reach the mid 60s this afternoon. Under some puffy instability cumulus clouds and a brisk northwesterly breeze, the official high temperature is likely to be the coolest since the 64° over 4 months ago on May 19. The next system moving in from the Great Lakes this weekend will have less moisture to work with, and indications from today's latest models are that the showers associated with it are likely to hold off until Saturday night.

Tonight and Tomorrow

Continued cool. Winds will diminish tonight, and lows will be near 50° downtown to the lower 40s in the cooler 'burbs. Tomorrow will see some increasing clouds in the afternoon, but only a 20% chance of showers before evening.

For the outlook through the rest of the weekend, scroll down to Camden's post below.

Tropical Topics

Tropical Storm Isaac has been moving a bit more west than expected in the central Atlantic, but it is still predicted to track well east of Bermuda, brushing by Newfoundland early next week. Its 45 mph peak winds increased to 60 mph this afternon, and strengthening to a hurricane is possible this weekend.

Climate Corner

The Weather Channel's new weekly "Climate Code" program, which premieres Sunday at 5, was previewed in the hometown Atlanta Journal-Constitution yesterday with an article, "Weather Channel ready to take heat on global warming" (requires minimally annoying registration). The associated broadband channel, One Degree, was previewed in Mediaweek.

Thursday, September 28, 2006

Severe Thunderstorm Watch Until 10pm


Showers, thunderstorms possible. Strong southerly breezes ahead of a strong cold front approaching from the west have pushed temperatures into the upper 70s this afternoon in the Washington metro area. Instability from the surface heating, lifting from the cold front, and strong upper-level energy support have prompted a Severe Thunderstorm Watch until 10pm for DC, northern Virginia, and central Maryland.

Storms are moving rapidly from southwest to northeast, so there may be some local downpours, but the main threat is not so much from heavy rain, but rather strong, gusty winds. There have been some reports of scattered trees down in eastern West Virginia. Click on your county above for the latest watches or warnings, and refresh the page for the latest radar loop from Let us know in the Comments section of any activity in your area.

For the outlook through the weekend and beyond, including Larson's Long-Range, scroll down to Josh's post immediately below, or click here.

"I" of the Storm

Tropical Depression 9 developed late yesterday and became minimal Tropical Storm Isaac this morning with peak winds of 40 mph (up to 45 mph in the latest advisory). It is expected to follow the usual path so far this year of staying east of Bermuda.

Capitol Climate

The WaPo has been, shall we say, somewhat lukewarm in covering the subject, as we noted Tuesday in PM Update, but the paper contains an editorial today, "Heed This Warning", using the latest report from climate expert James Hansen as the basis for strongly urging an end to the current inaction in Washington on the issue of climate change. It concludes,
Most of all, it will require an end to denial -- denial that the problem exists, denial that anything can be done about it if it does and denial that the problem is urgent and requires immediate attention.

Wednesday, September 27, 2006

Nice Now ... Gaining Rain Later?


Sunny, breezy.
A gentle southerly breeze and sunny skies have brought temperatures to the mid 70s in the Washington metro area this afternoon.

A cold front approaching from the Midwest could bring the possibility of showers by late tomorrow. For tonight's forecast and the outlook through the weekend, scroll down to Dan's post below.

Pictured: Yesterday was a great day for an outdoor lunch at Reston Town Center, by photographer Kevin Ambrose.

Precipitation Distribution: Drought or Naught?

Today is the 11th consecutive day without measurable rain in Washington, and it's been just under 2 weeks since more than 0.1" fell. Although August came in at barely 30% of the long term average, September is already nearly 40% above the average, so we're not talking about the dreaded "d" word here (especially since some folks tend to get quite exercised in the Comments section at any hint of such a mention; you know who you are!)

Looking back at the first 3 quarters of 2006, however, it does seem that there have been some interesting anomalies in the distribution of precipitation. The year so far, at just under 35", is comfortably above the 9-month average of 30". On the other hand, the 62 days with measurable precipitation are well below the average total of 85 for the year through September.

One way to look at this is by defining a "P/E" ratio (precipitation per event). This can be approximated by dividing the total precipitation for a month by the number of days in the month with 0.01" or more. (Strictly speaking, this is stretching the definition of "event", since one event can extend across multiple days.)

The chart shows that 3 of the 4 months beginning in June have had P/E ratios more than 50% above the long-term average. The August P/E of 0.34" per event was 89% of average, but the month's total rainfall of 1.03" was spread over only 3 days, or just 1/3 of the average number of August rainy days. The bottom line is that the year so far is running above average for total precipitation, but that total has mainly been achieved through a significantly smaller than usual number of events. chart from NWS data, photo © Kevin Ambrose

Tuesday, September 26, 2006

Sunny Skies, Superlative Shortage


Sunny. The superlative supply is running short: Afternoon temperatures are a couple of degrees cooler than yesterday in the Washington metro area, but mainly sunny skies and low humidity have combined to produce exceptionally fine early fall conditions.

Tonight and Tomorrow

Continued fine. After mainly clear skies and low temperatures in the mid 50s downtown to near 50° in the cooler 'burbs, tomorrow will again be sunny with highs around 77°.

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

Tropical Topics

The National Hurricane Center continues to report, "There are no tropical cyclones at this time."

Climate Corner

Evidence continues to mount that recent global average temperature changes are unusually extreme and near dangerous levels. A paper, "Global Temperature Change", by NASA climate scientist James Hansen et al. was published yesterday in the online version of the Proceedings of the National Academy of Sciences. Comparing Pacific Ocean sea-surface temperatures with the paleoclimate record, the authors determined that the global average temperature is now near the peak of the Holocene period (about 10,000 years). Furthermore, the recent rate of increase, 0.2°C per decade, if it continues for the next 50 years, will be enough to reach the maximum of the last million years, around the middle Pliocene. Articles about the study were published by the Beeb, UK Guardian, New Scientist, MSNBC (from, and Wall Street Journal (subscription required). The WaPo published only the AP report online, as did the NYT.

Monday, September 25, 2006

Fine Fall Fare


Sunny, cool. With the clouds from yesterday's cold front having retreated to central and southeastern Virginia and the Eastern Shore, it's a picture-book fall day in the Washington metro area. Temperatures by mid afternoon were into the mid 70s at most locations. The rainfall from the front was quite spotty, with DC and all of its contiguous suburbs receiving less than a measurable amount. If it weren't for the roughly 40% monthly excess of precipitation built up from the early part of the month, drought concerns could be developing. Despite the large excess of total rainfall, there have been only 6 days with measurable amounts this month, compared with the 30-year climatological average for September of 7.2.

Precipitation map for the 24 hours ending 8am this morning from NWS.

Tonight and Tomorrow

Seasonable. Lows tonight under mostly clear skies will be near 54° downtown to the mid and upper 40s in the cooler 'burbs. Tomorrow will again be sunny with highs near 77°.

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

Tropical Topics

The National Hurricane Center reports, "There are no tropical cyclones at this time."

Although it was still a strong storm with maximum winds near 70 mph, Helene lost its tropical characteristics, and the last public advisory was issued at 11am yesterday.

Mediarology: "I can't solve complex crimes in an hour."

The Weather Channel's highly-hyped Abrams and Bettes: Beyond the Forecast debuts tonight at 8pm, complete with its own web page. It was previewed in last Tuesday's PM Update.

Seasonal Outlook

Latest seasonal forecast: Click here.

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