The U.S. Drought Monitor through July 17 indicates moderate drought over much of the D.C. metro region, except far north and northwest areas which are abnormally dry. (U.S. Drought Monitor)

In Virginia, the area covered by drought grew by 6 percentage points between this week and last week (from 10 percent to 16 percent), spreading into Prince William and Fauquier counties for the first time. Much of Loudoun county is not yet designated as a drought area, but still classified as abnormally dry. 88 percent of Virginia is either abnormally dry or in drought. Consider at this time last summer, just 22 percent of the state fit this description.

In Maryland, the extent of drought remained about the same close to metro D.C., but grew in the southern part of the state. Overall, the area of the state covered by drought increased from 48 percent to 55 percent. Northwest Montgomery and Howard counties as well as Frederick county are not considered drought areas, but abnormally dry. 92 percent of Maryland is either abnormally dry or in drought.

Officially, Reagan National Airport has a rainfall deficit of 7.16” this year, Dulles 7.63” and BWI 8.72”. At Reagan National Airport, every month so far in 2012 has had below average rain (and/or snow), including July which is running 0.54” below normal.

Summer thunderstorms in the last couple weeks have produced heavy rainfall totals and even isolated flooding in parts of northern Fairfax county (e.g. around Reston, McLean and north Arlington), the District (especially just north of downtown) and central Prince George’s county. But these highly localized events have been insufficient to quell the expansion of drought conditions throughout the region.

Rainfall projection through Saturday indicates the potential for 1.5 to 2 inches of rain in the D.C. metro region (NOAA)

This evening an area of showers and thunderstorms is likely to come through the area, although it’s not clear how widespread it will be.

The best chance of widespread rainfall appears to be Friday afternoon into Friday evening.

Generally speaking, about 1-2” of rain is possible across the area through Saturday, although locally higher and lower amounts are likely due to the uneven nature of summer storms and convection.

Rainfall deficits at the airports this month range from about 0.5-1.5” - so perhaps the wet pattern into the weekend can help bring July rainfall to near normal levels.