Friday, September 14, 2007

Damp Friday Yields to Nicer Weekend


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 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.


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.

Wednesday, September 12, 2007

DC: Delightfully Comfortable


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. 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, 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".

Tuesday, September 11, 2007

Much-Needed Rain on the Way Out
Classic Fall Conditions on the Way In


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.

Monday, September 10, 2007

Goodbye, Gabrielle


Mostly sunny, hot, muggy. It's another hot and muggy afternoon in the Washington metro area with temperatures in the upper 80s to some low 90s and dewpoints generally in the upper 60s. Except for some very isolated activity on the Eastern Shore, showers and thunderstorms on radar are mainly confined to southern West Virginia. If no precipitation falls before midnight, it will be the 15th consecutive rainless day.

Tonight and Tomorrow

Warm, muggy, chance of showers. Warm and muggy conditions will continue overnight, with a 40% chance of showers or thunderstorms. Lows will range from the low or even mid 70s downtown to some upper 60s in the 'burbs. A stalled front in the region tomorrow will result in a partly sunny, muggy, day with a 40% chance of showers or thunderstorms and highs 84-87°.

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

Tropical Topics

Statistically, today is the average peak of the hurricane season, but there are no active storms in the Atlantic basin other than the departing Tropical Depression Gabrielle, which is accelerating eastward a couple of hundred miles south of Nantucket. The storm had maximum sustained winds of 35 mph as of the 5pm advisory.

Except for a tiny corner of coastal North Carolina, the drought-busting potential of Gabrielle was significantly under-achieved. Persistent northerly shear and very dry air to the west kept most of the precipitation offshore as the storm was more of a sandblasting event for much of the Outer Banks. The darkest blue on the NWS Precipitation Analysis map represents 0.25-0.5" of rain, and the lighter blues are less.

In breaking news on the bureaucratic front, ousted Hurricane Center Director Bill Proenza is reported this afternoon by the Florida Sun-Sentinel to be getting his old job back as Director of the NWS Southern Region.

Seasonal Outlook

Latest seasonal forecast: Click here.

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