After the Fall

Now

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.

Severe Thunderstorm Watch Until 10pm

Now

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 Wunderground.com. 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.

Nice Now ... Gaining Rain Later?

Now

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 Capitalweather.com 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.

CapitalWeather.com chart from NWS data, photo © Kevin Ambrose

Sunny Skies, Superlative Shortage

Now

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 LiveScience.com), and Wall Street Journal (subscription required). The WaPo published only the AP report online, as did the NYT.

Fine Fall Fare

Now

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.

Summer Ending on a Crisp Note

Now

Sunny, chilly. After morning lows of 50° at National and 43° at Dulles, temperatures have rebounded nicely, but they were still only in the upper 60s by mid afternoon. The Dulles low was only 1° above the record of 42° set in 1991. Today is the latest date in the year which has never seen a low below 40° there. Not only is the radar clear in all directions, but skies are virtually cloudless throughout the region south of the Mason-Dixon line.

Tonight and Tomorrow

Continued crisp. Lows tonight under clear skies will be chilly again, near 50° in the warmest urban areas to the low 40s in the coolest 'burbs. Get your excuses ready; tomorrow will be the perfect Friday for a "sick" day: Sunny, highs in the low 70s.

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

Pictured above: The map of surface pressure (solid lines) and 500 mb height (color shading) this morning from Unisys shows an unusually high amplitude pattern for late summer, with Helene moving around a high pressure area in the central Atlantic and our next weather maker, a strong low which brought substantial snow to portions of the central Rockies.

Tropical Topics

Hurricane Helene has turned north as expected well east of Bermuda, and a more easterly track is expected. Maximum winds are 80 mph.

The tropical wave west of the Cape Verde Islands hasn't become better organized yet, but gradual development is possible in the next couple of days as it continues moving westward.

Political Science

Today's NYT reports that, given the lack of action at the federal level, the state of California is suing the 6 largest auto makers over air pollution. The state Attorney General claims, "Global warming is causing significant harm to California's environment, economy, agriculture and public health." The suit is the first attempt to hold the companies liable for producing greenhouse gases. Articles on the lawsuit also appeared in the BoGlo (from the AP), LaTi, and UK Telegraph, among others. (Interestingly, the San Jose Mercury News has a story bylined from the WaPo, but a Google search of the online WaPo turns up only the AP and Reuters wire service reports.)

Feel of Fall

Now

Breezy, cool. Northwesterly breezes gusting as high as 25 mph at times have brought a definite fall feel to the Washington DC metro area this afternoon. With the sun impeded by the clouds associated with the large upper-level trough which helped bring the cold front through the area yesterday, temperatures are having a hard time reaching 70°. The highest official hourly reading has been 69° at 2pm, after which scattered clouds gave way to a broken overcast and a temperature drop of 3°. The fall crispness is especially noticeable with the dewpoint readings in the low 40s, which are as much as 20° below the level of 24 hours ago. The composite radar image shows virtually no precipitation east of the Rockies, except for some showers enhanced by the eastern Great Lakes and some thunderstorms in southern Florida.

Tonight and Tomorrow

Cool. Winds will diminish somewhat after dark, but persistence of the cloud cover with the trough aloft will prevent low temperatures in many places from reaching the levels which could be implied from the low dewpoints. Lows should range from the low 50s downtown to the upper 40s outside the Beltway. Tomorrow will be partly cloudy, less windy, and cool with highs around 70°.

For the outlook through Friday and the weekend, scroll down to Dan's post below.

Tropical Topics

After giving a quick hit to the Azores, Tropical Storm Gordon has weakened, although it still maintained its tropical characteristics this morning; peak winds were 60 mph. It is becoming extratropical after a journey of almost 10 days through the Atlantic. Maximum winds are now 50 mph; the last tropical advisory was issued at 5pm.

Hurricane Helene weakened slightly to 105 mph this morning. The storm has begun a northward turn, moving northwest at 9 mph. It is still expected to remain east of longitude 60W. Its strength, large size, and persistence in the central Atlantic, however, have caused swells to increase along the East Coast.

Potentially the next tropical system is a large wave with strong showers and thunderstorms several hundred miles southwest of the Cape Verde Islands.