Although rain was plentiful this summer, recent dryness is starting to creep up on the D.C. area.
The corn crop was remarkable this summer, the grass was luscious green but now lack of rain is starting to become a bit noticeable in the region.
As a matter of fact, the latest drought monitor, issued each week by the National Drought Mitigation Center, indicates the Washington area is abnormally dry. This designation precedes a moderate drought.
Notice how the abnormally dry designation matches well with the latest 60-day precipitation departures in the Mid-Atlantic. The DC area has seen the least amount of rain and thus has the highest rainfall deficit.
Looking back through monthly precipitation tallies, the rainfall deficit of 1.94 inches for September (so far) is the greatest deficit since November of last year. What has helped keep precipitation on target though for the year is the surplus seen in June; 6.19 inches above average. July was slightly above average for rain and August is when the dryness began. Rainfall was 1.59 inches below average. Note the precipitation departures in the graph below. Much of the year has been near average, with the significant spike in rainfall in June. However, the latest trends show less rain than average.
This is contributing to brown grass in spots and lower volume in area streams. The United States Geological Survey reports that a few streams in Maryland are running at 10% to 25% of their normal flow. Discharge is a great indicator of stream flow.
As for Washington, the Potomac River is still in great shape. Discharge is about 1,810 cubic feet per second at the USGS site near Little Falls. To put this in perspective, the lowest discharge recorded at this site is 121 cubic feet per second in September of 1966.
Ground water levels are still in fine shape but have been dropping at an accelerated rate since July. The nearest reporting site to Washington is in Dunkirk, Md., with water at about 43 feet below the ground. The record low is 49.19 feet set back in August of 2007. Given that groundwater levels fluctuate slowly, the dry pattern would have to continue for several more months to begin having problems with wells, etc.
The next threat for rain is Saturday, with potential of a half-inch as a cold front swiftly moves through the Mid-Atlantic. Beyond that, a dry weather pattern looks to take charge through much of next week.
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