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Posted at 11:00 AM ET, 09/ 9/2010

Drought getting closer to D.C. area

By Dan Stillman

* Sunday showers? Full Forecast | BWI sets record | Climate myths *

The latest U.S. Drought Monitor, issued this morning, places much of the D.C. area in the "abnormally dry" category. Shown above are the Drought Monitor maps for Maryland (top), West Virginia (left) and Virginia (bottom).

No doubt we're in a dry stretch. Aug. 22 and 23 are the last time more than a trace of rain was measured at Reagan National and Dulles airports, respectively. BWI's virtually rainless streak also goes back to Aug. 23.

According to the latest U.S. Drought Monitor issued this morning, the recent dryness and an overall deficit in precipitation for the year to date has much of the area classified as "abnormally dry" -- just a step away from "moderate drought" -- with the exception of D.C. proper and Prince George's, Howard and eastern Montgomery counties. From the Drought Monitor discussion:

Rainfall associated with Hurricane Earl (0.5 to 4.5 inches) prompted improvements in the drought conditions from Long Island to Maine. Away from the path of the hurricane, little to no precipitation fell across this region ... Across northern Virginia, abnormal dryness was expanded from the west toward the District of Columbia to reflect the field reports of deciduous trees dropping leaves and fruit earlier than normal due to lack of recent rainfall.

For the time being, the D.C. metro area isn't as bad off as outlying regions.

Keep reading for more on the status of drought in the D.C. area and beyond...

The biggest precipitation deficits (around 4 inches or more in the past 90 days) are focused from Frederick, Loudoun and northern Fauquier counties toward points west in western Md., northwestern Va. and the panhandle of West Virginia.

Departure (in inches) from the average amount of precipitation that would be expected during the past 90 days. Oranges and reds represent the biggest deficits (around 4 inches or more). Image credit: National Weather Service

Much of the W.V. panhandle and parts of western Md. have now entered "extreme drought" as of this morning's Drought Monitor, having received 40% of normal precipitation over the past 30 and 90 days. Southern Maryland and points east across the lower Eastern Shore are also struggling in the precipitation department.

The lack of moisture has hurt corn crops in areas such as Frederick, Md., and near Salisbury, Md., while a drought emergency could soon be declared in West Virginia. It's also increased the fire risk -- just yesterday much of the region was under a Red Flag Warning as "downsloping" winds from the west (blowing down the slopes of the Appalachian Mountains) brought with them incredibly dry air (relative humidity below 15% and dew points in the low 30s at National).

Locally, precipitation totals since Jan. 1 are below normal, though not terribly extreme...

National - Observed: 21.36"; Normal: 27.25"; Departure from Normal: -5.89"
Dulles - Observed: 26.59"; Normal: 29.27"; Departure from Normal: -2.68"
BWI - Observed: 28.26"; Normal: 29.39" ; Departure from Normal: -1.13"

We've seen worse in recent years, such as early last year as well as in 2007 into the first part of 2008. And we've had an above-normal precipitation month as recently as July, though February is the only other month to clock in on the plus side this year as observed at Reagan National.

In fact, the D.C. area is fortunate the drought situation isn't more dire right now, considering how hot the summer was -- warmer temperatures result in more evaporation of soil moisture. We got "lucky" with periodic and well-aimed thunderstorms during the summer, which have helped fend off drought conditions as defined by the Drought Monitor, but of course brought plenty of their own damaging impacts.

With drought essentially creeping toward the D.C. metro area from the west/northwest and south, the threat could become more serious if we don't see some decent rains as we get into the fall and toward winter. Prospects aren't great in the short term, with Sunday the only day in at least the next week having the potential for showers.

One factor that may not help the situation is the strengthening La Nina -- cooler-than-average water temperatures in the equatorial Pacific Ocean. La Nina can sometimes (but not always) favor a drier-than-normal fall in the mid-Atlantic.

The moral of the story is: Enjoy the cooler, mostly sunny and dry weather (with the possible exception of Sunday) now settling in, which we all deserve after surviving this summer's scorching heat and severe storms. But hope that it will soon be followed by some doses of appreciable rain. Drought is one extreme we could do without in this already extreme year of Washington-area weather.

By Dan Stillman  | September 9, 2010; 11:00 AM ET
Categories:  Droughts, Local Climate  
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Some interesting additional points on the dryness:

As David posted this morning, yesterday we saw some remarkable drying. After the front came through, downsloping winds (off the mountains) winds from the west dried us out to desert-like conditions. The relative humidity fell to 15% and we had dew points in the low 30s. At the same time, the temperature soared to 96. At 5 p.m., the temp was 94 and the dew point was 33 at Reagan National. That's a highly unusual combination for this area and much more typical in the SW U.S.

Many of you may have noticed the Fire Weather Watch and Red Flag Warning issued yesterday due to dry conditions and wind. Those have since expired, though burning conditions remain ripe.


Posted by: Jason-CapitalWeatherGang | September 9, 2010 11:21 AM | Report abuse

On the contrary, farmers in the Upper Midwest, with rainfall above normal, are expecting bumper corn and soybean crops--at a time when the crop failures in and around Russia have increased grain prices worldwide.

I'm not so sure of the situation in the Iowa Corn Belt--it's possible that TOO MUCH RAIN out there lowered their crop estimates. Iowa experienced flooding during July into August.

Conclusion: One of the major effects of global warming involves extremes in the distribution of precipitation patterns. We've seen that happen at both ends thus far during 2010.

Posted by: Bombo47jea | September 9, 2010 12:28 PM | Report abuse

Given how wet it is around her normally, I'm ok with "abnormally dry" being the new normal. Also, wasn't it worse earlier in the summer before we had that period of heavy rain over a week or so, maybe in late July?

Posted by: oldtimehockey | September 9, 2010 1:12 PM | Report abuse

A few showers on Sun will do little 2 end the dry cond. If these cond. cont. 4 another 8-10 days, we will move into an extreme fire danger. Looks like a tropical sys. is the only thing that will bring any rain in the next 2 weeks. At least we have the dancecast 2 look 4ward 2.

Posted by: VaTechBob | September 9, 2010 3:34 PM | Report abuse

Doug Hill has mentioned the need for rain most mornings lately when he's on WTOP.

Posted by: marathoner | September 9, 2010 3:45 PM | Report abuse

Bombo: could be. Global warming doesn't explain the similar or worse extremes in the 1930's. But if it is true that extremes in water vapor are increasing for the earth as a whole, then global warming sensitivity is low because extremes cool on average.

On the other hand, if water vapor increases evenly, then we will have much more feedback and ice cap melt, etc over the long run.

Posted by: eric654 | September 9, 2010 5:05 PM | Report abuse

Greetings from Provincetown/Cape Cod, CWG. Thank you for an incredibly insightful and informative post. As 'lead whiner' from the much-needed rain crowd, our ever-worsening drought status is cause for much concern.

Fully 6" below normal at National? While not "extreme", it is certainly significant. Worse yet, the metro area's reservoirs are located in the Potomac Highlands in Western MD and WV--precisely where our drought is the most severe. Let's hope reservoir levels do not drop to the point where we need water restrictions.

As usual, Bombo reiterates his distaste for rain by complaining about flooding in the Midwest.

On behalf of the MNR crowd, I abhor "abnormally dry" as the new normal. Any change in the pattern to return us to normal or above-normal precipitation will be gratefully welcomed.

Posted by: TominMichiganParkDC | September 9, 2010 9:30 PM | Report abuse

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