Busting out of the Drought
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...
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.
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...
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