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Posted at 03:01 PM ET, 09/27/2011

Washington D.C.’s wettest stretches: how do August and September compare?


Two-month rainfall totals over the mid-Atlantic and Northeast range from 15 to more than 30 inches in some areas. (NOAA)
With deluge after deluge over the past one to two months, just how wet has it been in Washington compared to past rainy periods?

Steve Zubrick, science operations officer at the National Weather Service forecast office in Sterling, Va., emailed the Capital Weather Gang offering some perspective. Zubrick analyzed the highest rainfall amounts over periods of different lengths since records have been kept in D.C. Generally, he found it’s been unusually, even historically wet, but not the top wettest.

First, Zubrick analyzed 30-day running precipitation totals, and found:

For Washington DC...the highest of an consecutive 30-day running rainfall total is 17.45” from Sep 1-Sep 30, 1934

The second highest consecutive 30-day running precip max was 16.61” that spanned 7- consecutive 30-day periods from Jun 13-19 through Jul 12-18, 2006 This period in 2006 covered the heavy rainfall that fell on Jun 25-26, 2006 that flooded parts of the DC metro region including Alexandria/Huntington.

In fact, the top 26 highest consecutive 30-day running totals in DC are all either associated with rainfall from the Sept 1934 maxima or the late Jun 2006 heavy rains.

So how does the recent wet period compare to 2006 and 1934? Zubrick found:

....the period spanning Aug 13-Sept 11, 2011 (inclusive) ... featured 15.03” of rainfall. This total ranks pretty far down in the pack (39th highest) of 30-day running totals.

Zubrick also analyzed the wettest one and two week periods, and reported:

The wettest 7-day (running consecutive day) period for DC: 11.37” spanning June 21-28, 2006. Note: nothing in 2011 ranks in the top 50 wettest 1-week list.

The wettest 14-day period for DC: again in 2006: 14.09” spanning June 18-July 2, 2006.

Lastly, he examined combined August-September rainfall totals since records began and reported:

...so far this year (2011), from Aug 1 through Sep 25 (inclusive), DCA has had 17.28” of rain. This ranks as the 3rd highest combined Aug/Sep rainfall for DC, behind Aug-Sep 1934 (22.66”) and Aug-Sep 1928 (18.70”)...and we still have 5 days left in the month.

There’s a slight chance we could break into second place with rain this week, but it’s highly unlikely we’ll pass 1934.

While the rainfall in D.C. over the past weeks has fallen just short of leading the pack historically, AccuWeather reports:

...several cities, including Philadelphia, New York City, Allentown and Baltimore, have had record rainfall for two consecutive months..

Related: What is August like in Washington? and What is September like in Washington?

By  |  03:01 PM ET, 09/27/2011

Categories:  Local Climate, Latest

 
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