Overall, this was the 28th warmest September on record and the 6th warmest of this young century.

DCA recorded a precipitation surplus for the first time this calendar year with 4.29” total. This places September 2012 as the 41st wettest in history (tied with 1928). The surplus broke an 8-month streak of drier than average months - the longest on record to start a calendar year. While DCA logged a modest surplus, Dulles and BWI recorded deficits yet again.

Temperature breakdown

Amazingly, DCA experienced a third of the month with lows in the cool 50s. In fact, four other days saw lows of just 60 degrees, so about half the days saw minima of 60 or cooler.

2012 continues to be the warmest year on record. With the September data, we now find DCA running 1.6F warmer than the second place tied years of 1991 and 2010. Here are the latest rankings:

Autumn cool down ahead?

The National Weather Service is forecasting October to be the first cooler-than-normal month in Washington, D.C. since October of last year. The developing pattern type does seem to support a cooler-leaning month, but we may end up closer to seasonal levels overall with plenty of variability. You can see the final National Weather Service outlook for October, 2012 for the U.S. here.

Further information

The National Weather Service publishes nice monthly assessments usually within a week of the close of each month (should be available shortly). You can click on your closest airport location here:

Reagan National (DCA)

Dulles Airport (IAD)

Baltimore-Washington (BWI)