Nice and Dry Belie July

Tonight and Tomorrow

Very Fine: Another rare non-AC DC July night is on tap with mainly clear skies and low temperatures in the low 60s in town, down to the mid 50s in the outlying areas. Tomorrow will be sunny with comfortable humidity and highs around 84.

For the outlook through the rest of the weekend and some suggested activities, see Camden's post below.

Omnimedia

You probably missed it if your copy of the Thursday weekly section was from the wrong side of the Potomac, but a couple of site visitors noted that the WaPo yesterday featured the local National Weather Service forecast office in Sterling. One interesting statistic: the 150 flash flood warnings issued in 3 days late in June were more than twice the number issued for all of the year 2005.

CapitalWeather.com's own Jason Samenow will be appearing in a panel discussion Tuesday night next week at the Koshland Museum of the National Academy of Sciences. The topic is "Get the News: New Media", the roles of new and traditional media in science news reporting.

The climate-change documentary "An Inconvenient Truth" is appearing in 562 theaters as of this weekend; total gross revenue so far is $13.6M. The Al Gore interview with Jon Stewart on the Daily Show is available on iTunes.

Improvement Continuing

Now

Decreasing humidity. Although the cold front which brought yesterday's rain moved through the area in the early morning hours, clouds behind the front were slow in clearing out. Nevertheless, temperatures this afternoon have rebounded to the upper 70s with decreasing humidity. National Airport bumped up to 80° at the 5:00 report.

Tonight and Tomorrow

Comfortable conditions. Skies will continue to clear tonight with very comfortable temperatures and low humidity. Temperatures in the low to mid 60s inside the Beltway could very well reach some mid 50s in the coolest 'burbs. Tomorrow will be sunny and dry with a few scattered clouds and highs in the low 80s.

For the extended outlook, see Josh's post below.

Summer Storms Summary

Local utilities are still struggling to catch up with the damage caused by the most recent round of storms which dropped heavy rains on already saturated ground. The NWS precipitation analysis for the 24 hours ending at 8am today shows rainfall coverage throughout the local region, but there was a wide range of amounts. Within about a 50 mile radius of the District, amounts were as low as under 0.50" (blue) to over 3" (red-orange).

There were three distinct "stripes" of heavy rain (yellow/orange/red) running generally towards the east-northeast; the heaviest amounts were well south of the Washington metro area, from near Richmond across the lower Chesapeake Bay and into the Maryland and Virginia Eastern Shore.

Climate Corner (Continued)

Today's WaPo has an editorial on the subject of "Acid Oceans", which we mentioned yesterday. News articles on the ocean acidity study published yesterday have also appeared in:

• San Francisco Chronicle
  
• Boston Globe (AP)
  
• USA Today
  
• St. Petersburg Times
  
• Anchorage Daily News
  
• Discovery Channel News
  

Tropical Topics

The tropics remain quiet.

Rain Remains

A Severe Thunderstorm Watch and Flash Flood Watch remain in effect for the Washington/Baltimore region; a Flash Flood Warning is in effect for DC and adjacent Virginia until 7:30.

Now

Showers and thunderstorms are located ahead of a cold front slouching southward toward the Washington DC metro area from central Pennsylvania and northern West Virginia. So far this afternoon, storm activity locally has been focused on the District and areas to the south and east. While National had almost half an inch of rain by mid afternoon, Dulles had received only 0.01", and many areas outside the Beltway in MoCo had seen at most a trace. Conditions will remain ripe through this evening for showers and thunderstorms to develop and move eastward to northeastward through the region. Some rainfall amounts may be locally heavy.

Tonight and Tomorrow

Showers and thunderstorms are likely (70% chance) through tonight. Lows will be in the upper 60s to near 70. Tomorrow will see clearing skies, lower humidity, and high temperatures near 80.

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

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Rain Records

Yesterday was the 50th anniversary of the world record 1-minute rainfall of 1.23" at nearby Unionville MD in 1956. The record lasted only 14 years; it was exceeded by the 1.5" which fell at Barot, Guadeloupe in 1970. The Australian Bureau of Meteorology has published a list of world extreme rainfalls through 1994, along with a comparison to Australian records. The National Academy of Sciences published a report analyzing the bounds on extreme precipitation events in 1994.

Climate Corner: Inconvenient Side Effects

Today's WaPo has a front-page article describing a joint NSF/NOAA/USGS report, "Impacts of Ocean Acidification on Coral Reefs and Other Marine Calcifiers", issued today on a serious side effect from the increase in CO₂ in the oceans.

Good Ol' Summertime

A Severe Thunderstorm Watch is in effect for the area until 11pm.

OK, you know the drill by now. It's summer, it's warm and humid (although a little less so than yesterday), there's an extra source of moisture from the high ground water content, and there are a couple of triggering mechanisms in the form of two weak frontal boundaries in the region and some upper-level instability rolling through this evening.

Accordingly, the NWS has issued a severe thunderstorm watch for the area until 11pm. The Flash Flood Warning for the Lake Needwood Dam in MoCo also continues. By 4pm, radar showed only isolated activity, some of which was locally intense, ranging over the map in location from upper MoCo (weakening as it moved eastward) to nearing Culpeper, to north of Charlottesville, and to west of Ocean City. The forecast for tonight through the weekend and beyond are below the fold.

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Climate Corner: Comedy Central Coverage

Last night's Daily Show on Comedy Central devoted half the program to an interview with ex-next President Al Gore on the subject of his climate-change documentary "An Inconvenient Truth". The show will be repeated this evening at 8pm and most likely during their holiday break next week.

And Now For Something Completely Different . . .

Right Now

Garden-variety (as opposed to the industrial grade of recent days) thunderstorms with some areas of heavy rain are affecting parts of the area this evening.

With the threat of storms, a Flash Flood Warning remains in effect for Montgomery County where seepage at a Rockville dam is a concern.

Tonight and Tomorrow

Tonight, it will be warm and humid with scattered thunderstorms and lows near 71° in the city, mid to upper 60s in the cooler 'burbs. Tomorrow will be mostly sunny and a little less humid with seasonable highs in the upper 80s and a slight chance of afternoon or evening thunderstorms.

For the outlook into the weekend, see Dan's post below.

Deficit Demolished

Water-weary Washingtonians woke Wednesday with wonder: Sunshine! Blue Sky! After days of near-Biblical deluges, the rain finally stopped. At National, the rain ended at 3:48 am this morning, to be followed by a few minutes of drizzle. The excess precipitation since Friday was more than enough to wipe out the accumulated deficit for the year. In fact, what had been a deficit over 30% quickly reversed to an even larger surplus of 32% through yesterday.

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

Metaphorical Meteorological Meanings

Tom Toles finds a symbolic interpretation of the recent storms in today's WaPo editorial cartoon. (Note to online WaPo: That omnipresent Sprint/Nextel Flash ad is a CPU HOG! It gets your window closed immediately on the PM Update computer every time. Talk about negative advertising!)

Moderate to Monsoon: State of Emergency

Flash Flood Watch is in effect for the entire DC area until Wednesday morning

State of Emergency declared in Washington, DC

9pm update: Heaviest rain is west of the beltway where the highest rainfall totals are likely tonight. Generally 1-3" should fall across the area (with isolated higher amounts--especially west) with rainfall tapering off late tonight. Rain may be enhanced as tropical low moves northward for a time between about 10pm and 3am. Washington Post: More Rain Heading to Washington.

6:45 Update:Flash Flood Warnings have now been issued for most of the immediate DC metro area.

5:30 Update: The low pressure area in the Atlantic moved inland near Morehead City NC before it could develop. However, it is spreading heavy rains and gusty winds across the Outer Banks as it moves northward.

To follow the current storm progress in the Washington area, periodically refresh the radar image from wunderground.com.
For storm related links and a timeline through tomorrow, scroll down to Matt's earlier post below.

With the lower half of the atmosphere almost completely saturated, storms can break out just about anywhere in the region the rest of this afternoon and evening, and storms now in central Virginia will continue moving north or west of north toward the DC area. Although some downpours may be brief, they can also be quite heavy.

After 2.56" of rain fell at National Airport in the 24 hours ending this morning, by early this afternoon, only 0.02" fell, but a heavy shower has raised that by 0.21" in only 14 minutes in the past hour. In an almost complete reversal of the usual thunderstorm path in this area, that storm moved from Prince George's County across the District from Southeast to Northwest, and is now pushing into Montgomery County, where rain is ranging from moderate to monsoon outside the window of Afternoon Blog Central. The main focus of activity so far today, however, is somewhat to the west of the immediate metro area. The most widespread heavy storms extend from near Hagerstown to south of Charlottesville.

Another issue of concern is a weak low pressure area about 35 miles off the lower North Carolina coast. The National Hurricane Center reported this afternoon that a reconnaissance flight found some gale force winds in the eastern portion of the area, but there was no closed circulation; therefore, it is not a tropical cyclone, at least yet. It does have the potential to develop into a tropical storm, however. Depending on the exact track of this disturbance as it moves northward, it could inject even more moisture into the DC region, or it could remain closer to the coast. In any case, the models are predicting several more inches of rain through the next day or so.

Flood Threat Continues

FLASH FLOOD WATCHES AND WARNINGS are in effect for the entire DC metro area. See details in the Current Watches and Warnings box above. Headed out for the commute home? Listen live to WTOP for the latest road conditions.

6:30pm Update: Light to moderate rain now falling in much of the metro area will become heavier at times in many places over the next couple of hours as stronger storms move in from the south.

For the outlook through tomorrow, and a recap of events since yesterday night, scroll down to Jason's post below.

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5:00pm Update: The Flash Flood Warning has been extended for DC and the immediate area except for Prince George's County until 11pm. An area of moderate to heavy rain extends from Springfield northward along much of the VA Beltway and is moving into western Montgomery County.

3:30pm Update: Storm activity is now located almost completely outside the Beltway. The heaviest showers are in southern Montgomery and western Fairfax Counties. Another area of moderate to heavy rain is in southwestern Prince George's County. Dulles has recorded 1.43" of new rain since 8am today. A band of storms extends southward just west of I-95 in Virginia to south of Richmond.

1:30pm Update: Right now, the local areas most affected by showers are in a narrow band from near Bowie southwestward across the eastern portion of DC through Alexandria and along I-95. Don't be fooled if you're seeing sunshine and some blue sky, as we are here in west-central Montgomery County. The air is extremely juicy; dewpoints in the area are in the low to mid 70s, and Stafford is reporting a super-tropical 81°. The sun just adds fuel to the mix, and bands of showers and storms extend (with some breaks) from north of Baltimore southward well into southern Virginia. These storms are moving a little east of north and will impact various parts of the DC region intermittently through the afternoon and evening, some with heavy downpours.