Summer-like winds generate mid-winter deluge in Washington, D.C. area

* Numerous flood warnings for rising rivers/streams in area | Flooding leads to water rescues across Washington area *


Car inundated from Goose Creek flood waters, south of Leesburg in Loudoun County. Driver required boat rescue. (Chris Cook)

A mad rush of warm, humid air from the sub-tropics triggered an unusual January episode of wind-driven rains over the Washington, D.C. metro region Wednesday night. West of the beltway, 2 to over 4 inches of rain fell, with widespread reports of flooding in northern Fauquier, Loudoun, northern Montgomery, and Frederick counties.

The setup for this event was much more characteristic of the warm season. Very strong flow from the south pushed record challenging warmth into the Mid-Atlantic, with temperatures surging into the 70s ahead of a powerful cold front.


Water vapor image last night shows deep flow of moisture up the East Coast from the Gulf of Mexico, extending into the sub-tropical Pacific

This super-charged flow carried deep moisture from the subtropical Pacific and Gulf of Mexico up the East Coast at high speeds, up to 90 mph just a mile above the surface. We call this feature a “low level jet” and it enables the efficient transport of vast quantities of moisture over large distances.


Surface winds show strong southerly flow up the East Coast around 11 p.m. last night (left). Winds about one mile up were around 80 knots or 90 mph Wednesday evening (right) carrying abundant moisture from the south. (Left, hint.fm/wind; right, weatherbell.com)

Weather Underground meteorologist Jeff Masters, in his Wednesday morning blog post, noted the storm system contained record levels of January moisture. Precipitable water - a measure of the available moisture in the atmosphere for producing rain - reached record or near record levels for January in numerous cities, Masters said. The precipitable water in Sterling, Va. Wednesday was 4th highest on record for January.


Radar around 11 p.m. Wednesday night showing waves of heavy rain pulsing from southwest to northeast generally west of the beltway (Weather Underground)

There was concern, due to some turning of the winds of height in the atmosphere, of tornado activity, prompting a “watch” from the National Weather Service (NWS). Although there was some weak rotation - which apparently produced a funnel cloud near Ft. Belvoir - no confirmed tornadoes touched down.

The NWS issued a number of severe thunderstorm warnings associated with the convective bands of rain coming through. The motivation was a concern the very strong winds at higher altitudes might crash down to the ground. But a very shallow layer of more stable air near the surface helped to attenuate the force of any downward transport of these raging winds. To be sure, winds were gusty at times, as high as 45-50 mph, but below damaging levels.


Doppler estimated rainfall totals from Wednesday and Wednesday night’s rain (NOAA)

By far, rainfall resulted in the greatest impacts. The highest totals exceeded 4 inches in Loudoun, Frederick and northern Montgomery county. An observer in Damascus, Md. reported an astonishing 6.15 inches of rain.

Link: List of rainfall totals and peak wind gusts

@capitalweather I guess it rained last night. The most standing water on summit of Bull Run Mountains I’ve seen. #cww twitter.com/paulcrumlish/s…

— Paul Crumlish (@paulcrumlish) January 31, 2013

Here are totals from our local airports:

Reagan National: 1.14 inches
Dulles: 2.32 inches (2” that fell Wed before midnight a daily record)
BWI: 2.00 inches

Flood warnings remain in effect for several area rivers and streams, which have yet to crest.

Jason is currently the Washington Post’s weather editor. A native Washingtonian, Jason has been a weather enthusiast since age 10.

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