It was a tame summer.
Reagan National, D.C.’s official reporting station, has seen only 24 days at or above 90 degrees this year, which is 12 days below average. And out at Dulles, there have only been 12 days at or above the 90 degree mark!
These are standout numbers for both locations, though certainly not unheard of in either recent or extended history.
Let’s put this up front: The average (via NCDC, and based on 1981-2010 temperatures) final date for 90s in D.C. is September 10. The latest it has ever (as far back as 1872) occurred is on October 11 in 1919.
Sticking with the NCDC averaging period, by the time we’ve made it through the first two thirds of September we’ve reached an expectation of 35.8 days of 90 degrees or higher. That’s compared to the 36.4 days seasonal norm.
While those odds may suggest a 90-degree day from here out about half of all years, they’re fattened by the fact that when one late-season hot day comes along, there is often another to follow. 21 of the past 30 years saw zero additional 90-degree days after the first two thirds of September. But half of those years that did saw two or more.
Of course, as recently as 2013 we’ve seen 90 degree readings into October. And in that case it was two, the latest of which was a torchy 91 on the 6th.
I’d be remiss not to note another official station in the region. As has been the case for what seems like about 12 to 18 months now, cool anomalies are even more impressive than the warm ones outside the city.
Out west at Dulles airport, a location often considered more representative of the western suburbs, the 12 days at or above 90 degrees this year puts it a stones throw from the fewest on record (since 1963) there of eight days.
As it stands, only six other years have recorded 12 or fewer 90-degree highs at Dulles. It is, in fact, the fewest since the record holder of eight in 2004, and the third time during the 2000s that Dulles has tallied so few.
Impressive numbers at Dulles, and the larger region for sure. When compared to the extraordinary high numbers in recent summers, it has almost felt like a dream at times. Extreme variability feels like a norm if nothing else.
As noted above, it’s a little soon to say goodbye to 90s without a doubt. The odds are not high, though.