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Posted at 10:09 AM ET, 06/17/2011

Thursday night’s rain provides needed soaking

Baltimore sets new daily rainfall record

Doppler indicated rainfall over the last 24 hours. (National Weather Service)
Generally half an inch to two inches of rain fell in the heart of the metro region Thursday night, at least temporarily quenching the thirst of area lawns and gardens.

Of course, there were some notable exceptions. Around Fairfax City, around 2.5” of rain fell, causing flash flooding. High water was reported at Woodburn Road and Frost Way, as well at Little River Turnpike and Wakefield Drive. At Roberts Road and Forest Avenue, vehicles were reportedly submerged.

Baltimore Washington International airport set a new daily rainfall record Thursday, with 1.96”, breaking the old record of 1.68” from 1948.

Some areas largely missed out on the rain, including portions of northeast Montgomery county and western Loudoun county.

Here are some reported rainfall totals:

Baltimore Washington International Airport: 1.96”
Reagan National Airport: 0.83”
Dulles Airport: 0.57”

NW Washington, D.C.: 1.25”

Vienna, Va: 1.45”
McLean, Va.: 1.14”
Great Falls, Va: 0.27”
Centreville,. Va: 1.02”
Fort Belvoir, Va: 0.69”
Manassas, Va.: 0.60”
Woodbridge, Va: 0.33
Round Hill, Va: 0.27”

Beltsville, Md.: 1.36”
Waldorf, Md.: 1.25”
La Plata, Md: 2.28”
Potomac, Md: 0.57”
Takoma Park, Md.: 0.58”
Germantown, Md: 0.47”
Frederick, Md.: 0.38”
Wheaton-Glenmont: 0.69”

(Data sources: Cocorahs network and National Weather Service mesonet)

Prior to yesterday’s downpours, Reagan National had accumulated a 1.32” rainfall deficit mid-way through June, following a shortfall of 2.12” in May. The U.S. Drought Monitor indicated “abnormally dry” conditions in eastern northern Virginia (i.e.. Fairfax county), the District, and central Maryland

GFS Model nailed it

Simulated rainfall by GFS model for 5 p.m. to 11 p.m. Thursday night. Dark green shade represents 0.5-0.75”, white shade 0.75-1”. (
In last night’s PM Update, I noted the GFS model simulated a deluge across the region, but I was skeptical it would pan out for several reasons: 1) The model had overforecast rainfall amounts on several previous occasions, 2) The best storm “dynamics” were north and northwest of the region, 3) We’ve been in a dry pattern (when in drought, leave it out).

It turns out, the GFS had an excellent simulation, predicting about 0.5-1” of rain over the region between 5 p.m. and 11 p.m. Of course, that was a little bit low, but models usually won’t capture the heaviest precipitation amounts in convective events. The model did a great job of picking up on the moisture potential from the southerly flow that streamed into the area which was squeezed out by the slow moving front and enhanced by the upper level dynamics (even if they were better north of D.C.).

By  |  10:09 AM ET, 06/17/2011

Categories:  Local Climate, Floods, Latest

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