September 2012 marks the eleventh month in a row of warmer-than-normal average monthly temperatures at Washington National Reagan Airport (DCA). The monthly difference from average this time was a relatively minor 1.2 degrees as we experienced a somewhat more balanced month of both warm and cool periods.
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.
For the overall month, we only hit 90 degrees three times, which was a big relief from the hot meteorological summer. We spent half the month with highs in the warm 80s.
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.
The warmer lows in the 70s occurred in the first eight days of the month. Two of those days - September 4 and 5 - set record high minimum temperatures. They were the only two records set at DCA during the month.
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.
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: