Most Read: Local

Posted at 12:45 PM ET, 10/04/2010

September 2010 hottest since 1980

After dry start, month ends wet

* Warmer later this week: Full Forecast | Potomac river's fall & rise *

From today's Print Edition:

By Martin Weil
September ended with record torrents of rain that may have washed away memories of one of the distinctive aspects of the month. It was one of the hottest Septembers in Washington history, continuing a trend of thermal overachievement that began here months ago.
According to preliminary National Weather Service figures, September's average temperature was 75.5, five degrees above average. That made the month the hottest September since 1980, when the average temperature was 77.1 degrees.
Since record-keeping for Washington began in 1871 (September temperature: 62.3 degrees), it appeared that last month was the fourth-warmest September recorded in the city.
The first three days of October have departed from the precedent set through the summer. The average temperature for Friday, Saturday and Sunday has been at least a degree below normal.
On Sunday, both the high temperature of 67 degrees at Reagan National Airport and the low temperature of 53 were considerably below normal.
As a result, the day's average of 60 degrees fell four degrees below the Sept. 3 average of 64.

The National Weather Service includes some additional details on September, 2010 in its September Climate Report for Reagan National Airport:

* It was the seventh straight month of above normal temperatures.

* The temperature reached or exceeded 90f ten days this month...the most during September since 1998.

* Washington D.C. has recorded 67 90f or higher days so far this year...tying the record set back in 1980 for the most number of 90f degree or warmer days in a calender year. [See also, this Weather Gang post: Going for the gold: National hits 90+ for 67th time]

* A daily record high temperature of 99f was broken on September 24, 2010...breaking the old record of 94f set in 1970. The 99f high temperature marks the latest time in a calendar year that Washington, D.C. has reached 99f or higher. The previous latest occurrence of 99f or higher was
September 8th in 1939...when it reached 100f. It was also the warmest temperature on record for Washington, D.C. during astronomical fall. The previous warmest temperature during astronomical fall was 98f on September 23, 1895.

*A daily record high minimum temperature of 74f was set on September 25th...breaking the old record of 73f in 1930 and 1970.

* Despite most of September being a dry month with measurable rainfall only occurring on three of the first 25 days of the month...a wet end of the month yielded precipitation totals well above normal for the month. September 2010 was only the second month since march with above normal precipitation...and the wettest month since December 2009 when 6.79 inches was recorded. [See also Rainfall records for D.C., Baltimore]

Additional reading:

Dulles Airport September Climate Report
Baltimore Washington International Airport September Climate Report

By  |  12:45 PM ET, 10/04/2010

Categories:  Local Climate

Read what others are saying

    © 2011 The Washington Post Company