Thursday, September 20, 2007

Crowds of Clouds Create Capital Cooling


Partly sunny, mild. A nearly stationary front extending northeastward off the Atlantic coast from a weak low pressure area in the eastern Gulf of Mexico has helped some cloudiness encroach westward into the National Capital region this afternoon. This has held temperatures down somewhat from earlier forecast levels. Mid afternoon readings were generally in the mid 70s, and humidity was a little higher with dewpoints near or a little over 60°. Precipitation on radar is confined to the southeastern corner of Virginia and eastern North Carolina. The main short-term forecast problem revolves around how persistent these clouds are likely to be.

Infrared satellite image at 3:40 this afternoon from Unisys

Tonight and Tomorrow

Considerable cloudiness, mild. Lows tonight under mostly cloudy skies will be generally in the low 60s, ranging to the upper 50s where fewer clouds persist, mainly to the west. Highs tomorrow under variable clouds will be 75-80°, but into the low 80s if more sun emerges.

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

Tropical Topics

A reconnaissance flight this afternoon investigating the area of storminess near Florida (Jerry wannabe) found a weak circulation in the eastern Gulf of Mexico about 115 miles west-southwest of St. Petersburg. Thunderstorms, as shown on the Tampa radar, remain rather scattered and disorganized, but the system has the potential to become a subtropical or tropical cyclone in the next couple of days.

Presentation: Hurricanes and Global Warming

The DC chapter of the American Meteorological Society has posted an announcement of the presentation next week by Chris Mooney on "Storm World, Hurricanes, Politics, and the Battle over Global Warming". RSVP is required by Monday.

For background on the topic (besides Mooney's excellent book), see Monday's posting by Kevin Trenberth on the Climate Feedback blog. Trenberth wrote a feature article, "Warmer Oceans, Stronger Hurricanes" in the July Scientific American. The SciAm article was critiqued by's Jeff Masters in his blog.

Wednesday, September 19, 2007

Still Seeking September's Seasonable Showers in Spectacular Sunshine


Sunny, warmer. It's a perfect day to sneak out early and mow the lawn with your pollution-reducing cordless electric mower, if you have any grass still alive to mow. A northeasterly wind and a slight increase in humidity (dewpoints up to the mid 50s) produced some morning low clouds which held temperatures down until bright blue skies once again appeared. By mid afternoon, temperatures were well into the upper 70s in most locations, and the traditional hot spot of Culpeper was 81°.

The down side, of course, is that much-needed rain is still not in the forecast. National is now below 25% of average precipitation month-to-date and just barely over 75% for the entire year. chart from NWS data, photo © Kevin Ambrose

Tonight and Tomorrow

Partly cloudy and comfortable. Under partly cloudy skies, lows tonight will range from the low 60s in town to the mid and upper 50s in the 'burbs. Patchy fog is possible in low-lying areas. Some morning clouds tomorrow should give way to abundant sunshine, slightly warmer temperatures, and a little more humidity with highs 78-82°.

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

Tropical Topics

The area of storminess over northern Florida and the adjacent Atlantic continues to show some strength as it drifts westward toward possible further development as a subtropical or tropical cyclone in the next couple of days.

Otherwise, the remnants of Ingrid are still dead.

Weather Biz: CNBC Meets the Weather Channel

Phil Flynn of Alaron Trading and recently-appointed Chief Strategy Officer Paul Walsh of Storm Exchange discussed "Fall Weather Risk" on CNBC's Squawk on the Street this morning. During the segment, the assertion was made that 30% of the economy is subject to weather-related risk.

The Storm Exchange calculates a "sweater index", which is the cumulative total of daily low temperature deviations below 60°. Warm weather in September is considered bad for retail sales because: (1) People have better things to do than shop at the mall, (2) Demand for winter clothes is low. Other indices provided by the Exchange include: the Thanksgiving travel rain delay index and the Labor Day BBQ index.

Tuesday, September 18, 2007

Continued Clear and Comfortable


Sunny, not quite as cool. This afternoon's weather map shows a large high pressure ridge extending from eastern Canada across most of the eastern half of the U.S. and into the northern Gulf of Mexico. Despite a light northeasterly breeze, the strong September sun (today's noon sun angle was 52°) has raised metro area temperatures generally into the low 70s, with a few higher readings. Culpeper was the warm spot in the region at 4pm with 79°; the major local airports were both 73° but BWI was a couple of degrees cooler. Humidity is also in the very comfortable range; dewpoints are in the upper 40s to low 50s. The nearest showers on the national radar map are over northern Florida.

Surface weather map at 1pm today from IntelliWeather

Tonight and Tomorrow

Clear and comfortable. Under mainly clear skies, lows tonight will be a little warmer than last night, ranging from the upper 50s downtown to the upper 40s in the 'burbs. Tomorrow will be much like today, but with highs 75-79°.

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

Tropical Topics

The main area of interest in the tropical Atlantic is a wave associated with some showers and thunderstorms off the Florida coast and over the Bahamas. The National Hurricane Center sees the "potential for subtropical or tropical cyclone formation over the next couple of days" as this system rotates westward around the large high pressure ridge across Florida and into the eastern Gulf of Mexico.

School Daze: $$$$$

Attention students (and anyone paying tuition for students): As another school year begins, the American Meteorological Society has posted a reminder of its various undergraduate and graduate scholarships in the atmospheric sciences. Most deadlines are February 8.

Monday, September 17, 2007

DC: Definitely Crispy


Clear, cool. After crisp morning lows as cool as the mid 40s in some places (50° at National and only 1° off the BWI record at 45°), temperatures have rebounded to the low 70s in most places under clear September skies. While dewpoints are not as arid as yesterday's upper 30s, they are still in the mid 40s.

Meanwhile, the continuing dryness has prompted Stafford County to impose water restrictions beginning today; the county has 139 days of water supply left in its 2 reservoirs, so crispy lawns may need to stay that way. A warming trend through the week should bring a return to readings near seasonable averages, but little or no rain is in sight.

Tonight and Tomorrow

Clear and cool. Clear skies and light winds will lead to lows tonight in the mid 50s downtown to the mid and upper 40s in many of the 'burbs. Tomorrow will again be sunny; highs will be a little warmer, 73-76°.

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

Tropical Topics

What had been Tropical Storm Ingrid was disintegrating as a depression last night, and advisories were discontinued at 5am.

A new tropical wave is located about 1000 miles east of the Lesser Antilles, but any development is expected to be slow. (That didn't stop it from being blamed for an increase in natural gas prices in commodity trading this morning, however.)

Climate Corner

Today's WaPo science 3/4 page (A7 for the dead-tree fans) is devoted entirely to the issue of the effect of climate change on species habitat ("Climate Change Brings Risk of More Extinctions"). Unfortunately, like many mainstream media reports, it confuses the issue by conflating the effects of bad wetlands conservation policies with the direct effects of sea level rise in the Chesapeake Bay.

Seasonal Outlook

Latest seasonal forecast: Click here.

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