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Posted at 10:30 AM ET, 05/13/2008

Busting out of the Drought

By Jason Samenow
Doppler rainfall estimates from the Sunday-Monday storm. The yellow shade is 2.5", the medium orange shade is 4", and the dark red is 6". Courtesy NOAA.

Related Washington Post story: Deluge Washes Away Area's Drought

It was just this past fall when Reagan National Airport (DCA) observed a record 34 days with no measurable rain. 2007 finished with precipitation 30-40% below average across the region. But for the most part, 2008 has been wet. May already ranks as the 5th wettest on record at DCA, and it's less than half way into the month. So as we've gone from extreme to another, what can we say about the drought? Is it over?

The numbers say yes. After one to three inches of rain Thursday and Friday and another three to five inches from yesterday's storm (with isolated 6"+ totals), we no longer have a short-term or long-term rainfall deficit (before our dry 2007, 2005 and 2006 were both wetter than average). And all drought indicators put us in the "green."

Keep reading and I'll walk you through them. See Matt's full forecast for the outlook through the weekend...

Observed vs. long-term average running precipitation totals over the last 12 months at DCA. The brown shading represents a rainfall deficit. The observed precipitation was less than the average precipitation up until this week. The green 'x' at the end of the graph shows the point where the running precipitation total finally exceeds the long term-average. Courtesy NOAA.

The first indicator is precipitation over the last 12 months. The above graphic shows a running tally of the observed precipitation, the jagged line, versus the long term average, which is the straight line. The shading in the middle represents the difference between them. For almost the entire year, the shading is brown, an indicator of a rainfall deficit. But notice at the very end of the graph, coinciding with Monday, the line representing the observed precipitation rises above the long term average for the first time. That indicates we've made up the rainfall deficit. I drew in a green 'x' to symbolize this point.

Latest Drought Monitor for Maryland and Virginia. Courtesy NOAA et al.

The next indicator, to the right, is the Drought Monitor for Maryland and Virginia. The Monitor, produced by Federal and academic partners, is released each Thursday. It synthesizes multiple drought indices, outlooks, and impacts on a map. As of last Thursday, even before the big the rains, the immediate metro area (counties adjacent to the District in Maryland and Northern Virginia) was not in drought according to this indicator. But just to the south and to the east, abnormally dry and moderate drought conditions persisted. As commenter Augusta Jim wrote Saturday:

The hydrological drought is no where near over [in central Va.].

Central Va. is down to only a 2 inch deficit for the year, with the recent rainfall, but remains close to a 15 inch deficit for the past 18 months.

Of course, he wrote this before the latest deluge. But even accounting for that, central Va. has a ways to go to make up for that deficit. Short term and long term drought indicators suggest portions of Delaware and southern Maryland are in a similar or worse situation. Fortunately, more rain later in the week should put yet another dent in the drought for all of these areas.

Just because many parts of the region are now caught up in the rainfall department doesn't mean we won't slip back into drought. We will need consistent rains through the summer into the early fall to maintain a healthy water supply. The forecast for the rest of this week has us on the right track...

By Jason Samenow  | May 13, 2008; 10:30 AM ET
Categories:  Droughts  
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Mini storm recap

Rainfall Totals since May 8

IAD: 7.11
8 - 1.46
9 - 0.85
10 - 0.29
11 - 3.73
12 - 0.78
(4.36 in one 24-hour stretch)

DCA: 7.71
8 - 1.32
9 - 2.22
10 - 0.22
11 - 2.63
12 - 1.32
(3.88 in one 24-hour stretch)

BWI: 6.15
8 - 0.34
9 - 1.85
10 - 0.27
11 - 1.49
12 - 2.20
(3.65 in one 24-hour stretch)

Posted by: Peter | May 13, 2008 11:11 AM | Report abuse

Peter--Nice breakdown. Thanks.

Posted by: Capital Weather Gang | May 13, 2008 11:25 AM | Report abuse

My thanks to Jason and CWG for the detailed drought status update, something several of us have been looking for! I appreciate the breakdown and the emphasis on the fact that, despite the recent deluge, DC metro could slip back into drought...and our near neighbors are still in a dry situation.

Posted by: ~sg | May 13, 2008 12:17 PM | Report abuse

Thanks for the great drought update post. It's good to know that we've made up the deficit (locally at least).

Posted by: Erika Froh | May 13, 2008 2:43 PM | Report abuse

Sounds as though Augusta Jim is (or was) still calling for rain. Enough!!! We now are so wet the farmers cannot plant their crops. What's now in the ground could fall prey to mold and waterlogging.

Posted by: El Bombo | May 13, 2008 4:42 PM | Report abuse

Most of my area received less than 1 inch of rain Sunday/Monday while the D.C. area was deluged with 3-6 inches.


Jerry Stenger, research coordinator for the state climatology office at the University of Virginia commented for the article, "Things have taken a turn for the better,but some of the areas in the Valley are not out of the woods yet. There are very likely a number of locations which could experience a serious deficit in available groundwater. The groundwater recharge during the growing season is relatively low, unless there is an unusually large amount of rainfall. What you've got now is pretty much what you're likely to be stuck with for the next few months."

A local rancher, Hunter Harris says, "We need an inch of rain every week for a while, if we don't get that, we're going to be in trouble."

Posted by: Augusta Jim | May 13, 2008 10:30 PM | Report abuse

What about the SE US? If water levels in the rivers there dont raise this summer the nuc plants will shut down creating a big time jump in electric rates and possible black outs throughout the East.

Posted by: Anonymous | May 14, 2008 11:04 AM | Report abuse

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