Monday, February 4, 2008

Super Soaker: Record Rain Recap

This morning's showers, while generally minimal across the metro area (a couple hundredths of an inch), helped add to a nice surplus for February built up from Friday's record-setting rainfall. The regional 24-hour precipitation map (popup image) ending 7 a.m. Saturday from the National Weather Service (NWS) Precipitation Analysis shows that National Airport and a good chunk of the eastern half of the District were in the sweet spot, with the heavier amounts (shaded in yellow) blossoming out even wider through the entire Baltimore Beltway vicinity and northeastward toward Pennsylvania. Some amounts as high as 3" were reported just over the Mason-Dixon line. Even in the less-rainy parts of the immediate metro region, amounts up to 1.5" (dark green) were widespread.

The virtual rain gauge for the three major local reporting stations (click image to enlarge) shows the rainfall accumulation in three-hour intervals from 4 a.m. through 7 p.m. Although precipitation started earlier at Dulles (0.01" actually fell before 4 a.m.), the three totals were coincidentally precisely equal at 0.81" by 10 a.m. Notice that, after diminishing somewhat in the morning, the rainfall rate picked up dramatically at both National and BWI in the afternoon. Nearly half of the final total at National fell from 1 to 4 p.m. This is a typical pattern in large storms; the precipitation begins slowly as warm air overrides colder air near the surface, then increases in intensity toward the end as deeper, more convective-type showers take over. There were a few unofficial reports of thunder with this storm.

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