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Posted at 10:52 AM ET, 12/08/2011

The record breaking rain storm of December 7, 2011


Washington, D.C.’s daily rainfall records by month. Wednesday’s 3.1” of rain was the most ever in December and higher than the highest of all months between November and March.
Wednesday’s storm had it all: heavy mountain snow, raging wind, and severe thunderstorms in the Virginia Tidewater and southern Maryland. But it was truly exceptional as a rain-producer, and the wettest day Washington, D.C. (as measured at Reagan National Airport, DCA) has ever experienced during the cold season spanning November to March.

THE RAIN

Reagan National’s daily rainfall total was 3.10”, setting both daily (previous record 1.34” from 1971) and monthly rainfall (previous record 2.81” from 1977) records. More rain fell Wednesday than it does in an average December (in its entirety), 3.05”. It was the 57th wettest day in D.C. weather records since 1871, or in the 99.9th percentile for rain events. 2011 has now accumulated 45.33” of rain at DCA, almost 8 inches above average.


Doppler estimated rainfall indicates 1.5-2.5” of rain was most common in the D.C./Baltimore region, but isolated amounts were measured by observers. Doppler radar can underestimate rainfall sometimes. (National Weather Service)

Daily rainfall records were also set at Baltimore Washington International Airport and Dulles, which received 2.38” (old record 1.27” from 1976) and 2.14” (old record 1.13” from 1976), respectively.

Other select rainfall amounts (from different sources):

Maryland


Brandywine, 2.76” (Cocorahs)
Calvert County, 2.43” (Wes Junker, CWG)
Camp Springs, 2.46” (Cocorahs)
Columbia, 1.98” (Cocorahs)
Frederick, 1.15” (Cocorahs)
La Plata, 2.44” (Cocorahs)
Rockville, 1.8” (Cocorahs)
Severn, 2.02” (Cocorahs)
Silver Spring, 2.45” (Cocorahs)
Takoma Park, 2.24” (Cocorahs)
Wheaton/Glenmont, 1.4”(Cocorahs)

Virginia

Alexandria, 1.84” (Cocorahs)
Hamilton, 1.6” (worldtraveler83, Capital Weather Watcher)
Leesburg, 1.41” (Cocorahs)
Lorton, 2.42” (Cocorahs)
McLean, 1.93” (Cocorahs)
Remington, 2.51” (Cocorahs)
Stafford, 2.3” (Cocorahs)

The heavy rain resulted in many reports of flooding - of streams, roads, and basements...

HOW MUCH SNOW WOULD HAVE FALLEN IF IT HAD BEEN COLDER?

We get this question all the time and it’s unanswerable. Cold season heavy rain events typically have prevailing winds from the south which pump in tropical moisture whereas snow events typically have winds from the drier north direction, so it’s comparing apples and oranges. Rain events necessarily will have more moisture to work with.

To drive this point home further, the rainfall output from Wednesday’s storm was greater than the liquid equivalent from D.C.’s two biggest snowstorms on record. The Knickerbocker storm of January, 1922 produced the liquid equivalent of 2.81”(28 inches of snow) and the blizzard of February 1899 produced the equivalent of 2.08” of rain (20.5” of snow). Even the most extreme snow events don’t have the water content of rain events.

THE SNOW

Accumulating snow was generally limited to high elevations in central/western Maryland and western Virginia, including the Shenandoah. Capital Weather readers S.P. Gass reported 4.5” at 1,900 feet in Warren County. Reports of bursts of snow and/or snow mixing with rain were common in D.C.’s north and west suburbs but most locations did not get any accumulation.

Here are some reports from the National Weather Service:

Maryland

Damascus, Md.: Trace
Fort Ritchie (Frederick county): 2.0”
Wolfsville (Frederick county, elevation 1,250): 1.8”

Virginia

Reagan National Airport: Trace
Big Meadows (Madison county): 2.5”
Bluemont, Va. (Loudoun county): 4.0”
Herndon, Va.: Trace
Winchester, Va.: 0.2”

THE WIND

As the storm rapidly deepened, winds accelerated last night, resulting in some impressive gusts in the 40-50+ mph range and scattered power outages. Here are some the peak gusts aggregated by the National Weather Service:

Maryland

BWI Airport, 46 mph
Flint in Frederick county, 56 mph
Laytonsville, 50 mph
Patuxtent River, 51 mph

Virginia

Reagan National Airport, 39 mph
Winchester, 41 mph
Sterling, 45 mph

READER REACTIONS/REPORTS

Here are some fun Tweets and Twitter messages collected during the storm (wait a few seconds for these to load)

Ian Livingston contributed to this post.

By  |  10:52 AM ET, 12/08/2011

Categories:  Local Climate, Latest, Recaps, Floods, Winter Storms

 
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