Moderate precipitation deficit persists into 2008
While enough to get you wet without rain gear, today's semi-springlike showers have done little to dampen the impact of a prolonged dry spell in the Washington metro area. Rainfall amounts of around a tenth of an inch or less have barely equalled the long-term daily average, although more rain is possible tonight. With only two days left in the month, there have been only six days, counting today, with measurable precipitation (0.01" or more). That is less than two-thirds the average of 9.8 rainy/snowy days in the average January in the base period of 1971-2000. Total precipitation for the month is less than 50 percent of the "normal" (long-term average).
The regional 30-day precipitation percentage of average from the National Weather Service (NWS) Precipitation Analysis shows a lot of sub-average yellows and oranges, with the near to above-average grays and greens mostly limited to parts of the Northern Neck of Virginia and southern Maryland. The intensity of the dryness increases generally northward and westward of the Beltway, with Montgomery, Fairfax, and Loudoun Counties faring the worst within the near 'burbosphere.
Looking back at the last six months, the picture isn't any better, with large areas in the range of 75 percent or less of average. A sizable chunk of central Loudoun County is in the 25-50 percent bracket (and we're not talking tax cut proposals in this primary season). Outside of far western Maryland, there's virtually no above-average area south of the Mason-Dixon line.
The dry conditions have prevailed into this year from an also very dry 2007. The chart at the top of this post shows the monthly percentage excess or deficit of precipitation. Only April (+50%) and October (+103%) were substantially wetter than usual. Although October was quite wet, by far the greatest portion of the rainfall came in the four inches that fell on the 26th-27th. That two-day amount was nearly one-eighth of the total for the entire year. The number of rainy days was only 5, compared with 7.2 in an average October. August and December were marginally above average, but the other eight months all contributed significantly to the yearly deficit of 16 percent, especially the consecutive months of May, June and July.
Fortunately, the situation hasn't reached the magnitude of the "Exceptional Drought" classification as it has in the interior Southeast, but large portions of Virginia and central and southern Maryland are in the Moderate Drought category. Since it's clearly too warm right now for the white stuff, disappointed snow fans might want to consider doing a rain dance instead. The effects will be less obvious now that stuff isn't growing, but your lawn, shrubs, trees and water supply will thank you in the spring.