Crowds of Clouds Create Capital Cooling

Now

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 nature.com Climate Feedback blog. Trenberth wrote a feature article, "Warmer Oceans, Stronger Hurricanes" in the July Scientific American. The SciAm article was critiqued by wunderground.com's Jeff Masters in his blog.

Still Seeking September's Seasonable Showers in Spectacular Sunshine

Now

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.

CapitalWeather.com 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.

Continued Clear and Comfortable

Now

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.

DC: Definitely Crispy

Now

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.

Damp Friday Yields to Nicer Weekend

Now

Cloudy, muggy, light showers. Precipitation sandwiched between a strong cold front through the Great Lakes and Ohio Valley and a weak warm front through the Carolinas spread rapidly northeastward this afternoon, but the heaviest amounts were over and to the west of the mountains. By mid afternoon, each of the 3 major airports had reported a trace of rain; Frederick had 0.01".

Temperatures in the metro area are generally in the mid to upper 70s, but dewpoints are in the muggy mid 60s. Behind the cold front, temperatures in the upper Midwest were in the upper 40s shortly after lunch time.

More showers are likely overnight before cooler and much drier air arrives for the weekend.

Tonight and Tomorrow

Showers, then clearing and cool. There is a 40% chance of measurable rain through early evening (more likely to the north and west) and a 60% chance of showers overnight. Lows will be in the mid 60s downtown and in the low 60s to near 60° in the 'burbs. Cloudy skies should clear from west to east tomorrow morning along with decreasing humidity and gusty northwesterly breezes. Highs will be 72-76°.

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

Humberto's History, Ingrid Increases Intensity

After setting the record for fastest intensification from first advisory to hurricane, Humberto quickly became history yesterday, although its moisture brought some drought relief to extremely parched areas of the Southeast. Stu Ostro of The Weather Channel has an excellent retrospective (with pictures) in a series of blog posts.

Ingrid, about 750 miles east of the Lesser Antilles, is a little stronger today at 45 mph, but it is still expected to be weakened by wind shear to a depression without reaching hurricane strength.

Climate Corner: Tropical Topics

This month's American Meteorological Society (AMS) Environmental Science Seminar Series presentation is "Hurricanes and Global Warming: Where are we now?". The seminar is scheduled for next Friday, the 21st, from noon to 2:00 in the Dirksen Building. The public is invited; reservations are not necessary, but registering on the web will allow you to bypass the registration table.

This is also the topic of the DC AMS presentation by Chris Mooney the following Wednesday, the 26th.

Jeff Masters discusses the topic "Humberto and Felix--a sign of climate change?" in his wunderground.com blog post today.

Some new material on the topic of a possible hurricane/climate change connection was published in last week's (September 4) issue of the American Geophysical Union's EOS Transactions (subscription required). The papers "Misuse of Landfall as a Proxy for Atlantic Tropical Cyclone Activity" (Holland) and "Atlantic Tropical Cyclones Revisited" (Mann, Emanuel, Holland, and Webster) both provide new statistical evidence to support the notion that increasing intensity of Atlantic tropical cyclone activity is real and not an artifact of improved observational technology.

For more background on the subject, see MIT Prof. Kerry Emanuel's 2007 AMS Haurwitz Memorial Lecture. It's available for viewing online in both Windoze Media and Quicktime format.

Mediarology

The subject of "Hurricanes & Climate Change" will also be covered on this weekend's "Forecast Earth" on The Weather Channel (5pm Saturday and Sunday):

Will we see more hurricanes in a warmer world? The latest research contains new clues about global warming's influence on the number of hurricanes. We go to the leading climate experts for answers.

DC: Delightfully Comfortable

Now

Clear, warm, low humidity. The last time this headline appeared in PM Update was May 22. Unless you're a lawn, a garden, a farm field, or someone economically dependent on one of those things, it's a delightfully sunny and dry day in the National Capital region. After hitting an official low of 64° (59° at Dulles), temperatures have rebounded mainly to the upper 70s and some low 80s under crystal clear blue skies this afternoon. By 4pm, National had reached at least 79°. Dewpoints are in the extremely comfortable mid and upper 40s.

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

Tonight and Tomorrow

Clear and comfortable. With clear skies, light winds, and low humidity, temperatures should be able to drop to the upper 50s downtown and the low and mid 50s in the 'burbs with some upper 40s in outlying areas. Tomorrow will again be sunny and warm with low humidity, highs 78-83°.

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

Tropical Topics

A stormy area off the Texas coast and the tropical wave in the Atlantic mentioned yesterday were vying to be the next tropical cyclone, and they were each declared tropically depressed at 11am this morning. The Texas one has gone on to become Tropical Storm Humberto. It's too close to the coast to develop much stronger winds, but its slow movement will pose the threat of considerable flooding to the Houston area. The mid-afternoon Houston radar, courtesy of wunderground.com, shows a very small, but well-developed circulation.

Tropical Depression 8 (Ingrid wannabe) is expected to strengthen to a tropical storm in the next couple of days but not to intensify rapidly after that as it aims toward the northern Caribbean islands.

Gabrielle is gone, but apparently there was quite a commotion in the blogosphere over the weekend regarding some highly hyperbolic scenarios for the East Coast. That was not the case here (see Friday's PM Update), although one local broadcast outlet was observed on multiple occasions at least partially buying in to the alternate reality of some outlier models. The Weather Channel's Stu Ostro has a very nice recap of the situation in his blog posting, "Getting Wiggy with Gabrielle".

Much-Needed Rain on the Way OutClassic Fall Conditions on the Way In

Now

Cloudy, muggy, showers. After persistent summer heat in the first third of the month, the crashing sound you heard today was that of busting temperature forecasts (see yesterday's PM Update for a prime example). The lingering, but much-needed, showers have kept temperatures to the low and mid 70s this afternoon in the metro area.

Through early afternoon, National had recorded slightly under half an inch of rain, and Dulles was closer to two-thirds. The NWS Precipitation Analysis to the right shows a healthy band (dark blue) of quarter to half-inch rainfall across DC and the Beltway vicinity, with some higher amounts (green) around Dulles and also to the south.

Clearing and drying overnight following a cold frontal passage should lead to a much more pleasant and fall-like midweek.

Tonight and Tomorrow

Showers ending, clearing, comfortable. Showers will end from west to east by early this evening, and clouds will decrease toward morning, along with lower humidity. Lows will range from the low and mid 60s in the urbosphere to some upper 50s in the outer sub-urbosphere. Tomorrow will be sunny and comfortable with northwesterly breezes and highs 78-82°.

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

Tropical Topics

Tropical Depression Gabrielle was dissipating as it moved eastward well south of Nova Scotia, and the last advisory was issued at 11 this morning.

The showers and storms associated with a tropical wave over 1000 miles east of the Windward Islands were weaker this morning, but the area still has the potential to become a depression in the next couple of days.

Awesome August

Matt noted earlier the record summer heat and significant dryness in the DC area. August conditions were even more extreme in other parts of the country. The Weather Channel's Dr. Greg Forbes recently posted a discussion of those extremes. Several Midwest locations, including Madison WI, Rochester MN, and Rockford IL, had their wettest month ever, while seven others had their wettest August. Opposite records were set in Missouri, Arkansas, North Carolina, Kentucky, and Michigan, where several places had their driest August or even driest month ever (North Little Rock, 0.01").

In the temperature department, a number of places had their warmest month on record. These were in Alabama, Florida, Georgia, Kentucky, Mississippi, the Carolinas, and Tennessee. An additional 20 stations in 13 states had their all-time record warmest August.