Friday, June 2, 2006

Breaking the Dry Spell?

The two essential ingredients for showers and thunderstorms are moisture and vertical motion. With dewpoints at the ground from 68° to 72°, there is plenty of moisture around. The vertical motion for yesterday's storms was provided mainly by heating: a threepeat in the form of a third consecutive day of 90°+ temperatures.

Today is a somewhat different story, since a persistent high overcast has limited temperatures, at least by mid afternoon, to the low 80s. (This overcast, which has nevertheless allowed a fair amount of strong June sun to penetrate, led to forecasts for today ranging from 76 on a certain cable channel to 80 from the local NWS. For a check on how PM Update did, scroll on down to here).

Vertical motion is being helped today by a nearly stationary front draped across Pennsylvania. Therefore, more widespread storm activity is possible late this afternoon and through tonight. The NWS has issued a flash flood watch for Washington DC and the immediate area. By mid afternoon, radar was showing storms widely scattered from near Hagerstown to southwest of Richmond. These were generally moving northeast.

Tonight and Tomorrow

Showers and thunderstorms are likely late this afternoon through tonight. Some locally heavy downpours could produce flash flooding. Lows will be in the mid to upper 60s. Some showers may linger through early afternoon tomorrow, especially in the eastern portion of the region, with gradual clearing later in the day and highs in the mid 70s.

Yesterday's Rain

The map from the NWS of total precipitation centered roughly on DC shows that yesterday's rainfall was quite disappointing in much of the metro area. Except for a very small portion of far western MoCo where amounts were as high as possibly 2.5", most of the area saw 0.1" or less, and large portions of the District and adjacent Virginia were completely dry. Official DC reports were a trace at National and a whopping 0.02" at Dulles. BWI, which benefited from stronger storms in the Baltimore area, had 0.24". Amounts were also higher over the Bay and large portions of the Maryland Eastern Shore.

Climate Corner

The climate change documentary, "An Inconvenient Truth", which opens today in several area theaters, is reviewed in today's WaPo Style.

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