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.
Only four days into the month, the official Washington rainfall total is already at 78% of the long-term average for the entire month of February, and the more than 50% deficit from January is nearly all erased. Through yesterday, the year so far is within less than a tenth of an inch of the long-term average. But the accumulated deficit from last year still remains, and while the overall drought situation is improved, we're still not out of the woods in the long run.
In the 67 years since the official observation location moved to National Airport, this is apparently only the fourth time that precipitation has totaled 2" or more on a single calendar day in February, exceeded only by the 2.27" on the 22nd and the 2.14" on the 16th, both in 2003. In fact, there have been only 24 instances of 1" or more of daily precipitation in February during that period. Consistent with the fact that most heavy precipitation events in Washington are rain, even in the winter, only nine (slightly over one-third) of those events had measurable snow. The heaviest amount was 16.4" on the 11th in 1983; only two others were in double digits.
For a typically excellent illustrated analysis of the early evolution of this storm, see Stu Ostro's post, "Another Feisty System," at The Weather Channel's blog.
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