Not Your Typical May - Or Was It?
By Don Lipman, Guest Contributor
If you're an outdoor tennis enthusiast, as I am, there wasn't much to cheer about last month. We didn't set any monthly rainfall records and barely broke a daily record (on the 26th), but it wasn't for lack of trying.
Though you may think that we haven't had such a rainy May in a long time, think again. We need go back only one year -- to 2008 -- to find a wetter May. In fact, May 2008, with 10.66 inches of rain (one third more than last month), was our third wettest May since records began, at least at Reagan National Airport (DCA), which is Washington's official measuring station! Including the weather records prior to DCA dating back to 1871, May 2009 will go down as the 6th wettest May with 8.05 inches.
It was probably the number of rainy days (21) last month that made it particularly unpleasant. Average is only 11. It's like comparing Seattle's annual precipitation to that of D.C. Most people would say that Seattle has a much rainier climate--and it does, but only because there are many more days (38% more) of overcast, drizzly days than in D.C. Annual precipitation, however, is actually slightly less in Seattle than in D.C.
Keep reading for more on May's weird weather, or was it...?
Actually, soggy Mays are not unusual at all in Washington. Statistically, it's the wettest month of the year--again, at DCA. From 1970 to 2000, the period upon which the current averages, or normals, are based, May has averaged 3.82 inches of rain (though September is a close second, averaging 3.79", and is one day shorter). By comparison, the driest month is February, but on a technicality because it's so short.
The wettest month ever (at least back to 1870) in D.C. was September 1934, with 17.45 inches of rain, an amount so large that it undoubtedly resulted from one or more tropical systems. And just for good measure, the driest month ever in D.C. was October 1963, when only a trace of rain fell. Finally, the wettest year of all was 1889, which piled up 61.33 inches (over 55% above normal) and the driest was the dust bowl year of 1930, which could only muster 21.66 inches of precipitation (45% below normal).
In the thermal department, the highest recorded temperature was 86°, one of the rare instances in which April's high temperature (92°) exceeded that of May. Otherwise, it was a fairly typical month, averaging 65.5 degrees, just .1° below normal (at DCA) but on the warm side at Dulles (IAD), which averaged 65.0 degrees, or 2.7 degrees above normal. (Average temperatures are so much lower at Dulles primarily because of the lower nighttime temperatures.) There were no daily temperature records set.
Following are a few of the May weather highlights at the Reagan National (DCA) and Dulles Airport (IAD) measuring stations:
|Highest temperature||86° on the 9th||86° on the 23rd|
|Lowest temperature||45° on the 19th||38° on the 19th|
|Highest low temperature||68° on the 24th/25th||66° on the 16th/24th|
|Lowest high temperature||56° on the 4th||56° on the 4th|
|Consecutive days with a trace or more of rain (a dreary period)
||1st to the 9th||1st to the 9th|
||26th - 1.65"||26th - 3.59"|
|A trace or more of rain fell on...||21 days||20 days|
I'll leave you with a couple more interesting bits of climate trivia, courtesy the National Weather Service:
- At DCA, total rainfall for the first three months of 2009 was just 5 inches, the fourth driest such period on record. In contrast, the April-May two-month period totaled 12.27 inches, making it the 5th wettest such period.
- At IAD, May 2009 tied (with 1988) for the wettest on record (where records date back to just 1963) with 10.26", and was the wettest month there since June 2006.
About the author: After a 30 year "Intelligence Community" career, Don's second life focuses on tennis and weather. When not on the courts, he writes weather articles, which have appeared in community newspapers/newsletters and gives weather talks at senior centers and on cruise ships. He's doing a weather "gig" on the Emerald Princess on August 24th in the Baltic. Interested in going along?
Capital Weather Gang
| June 2, 2009; 10:00 AM ET
Categories: Lipman, Local Climate
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