The Washington PostDemocracy Dies in Darkness

We predict the coolest and wettest October in 11 years in D.C.

It may be hard to come back from this cold and wet start to the month

A visitor to Georgetown Waterfront Park checks to see if it’s still raining Sunday. In the background is the Kennedy Center. (Jeannie In D.C.)

October is rolling in like a chilled pumpkin beer. Monday morning’s lows in the 40s came two weeks ahead of the first instance of 40s last year in Washington. Highs in the 50s are also a sharp contrast to the 80s on this date in 2021. With over an inch of rain already, October has experienced a dismally cool start that will be hard to overcome by Halloween.

Our October outlook favors temperatures to near to below normal — 0 to 3 degrees cooler than the 30-year average of 60.8 degrees; last year’s average was a very warm 66.3 degrees.

We project rainfall to be near to above normal, 0 to 0.5 inches above the 30-year normal of 3.66 inches; last year registered a slightly dry 3.27 inches.

Our most recent cooler-than-normal October was 2015, while our most recent wet October was 2020. But our most recent cool and wet October together was 11 years ago.

The 15-day outlooks for the United States from different computer models project cooler-than-normal weather for the eastern U.S. with near-average rainfall for the Mid-Atlantic, mostly from the storm we’re seeing now:

The next week after this current rain is forecast to be dry, but we would still have two more weeks to make up the 1 to 2 inches of rain needed to match or exceed normal, given the very wet start.

The main culprit for this pattern is a persistent zone of high pressure in western Canada that is causing the jet stream to dip over the eastern United States.

September recap and year-to-date

September was a mild and dry month. The average temperature was 0.3 degrees warmer than normal at 72.7 degrees, giving us the 31st-warmest September in the historical data set originating in the late 1800s. The 2.27 inches of rain was 1.66 inches drier than normal and the 54th-driest in the historical data set.

For the second straight month, there were no temperature records set at the three major D.C.-Baltimore airports.

Here are the daily details for Washington’s September:

The month exhibited an impressive temperature range from the hot 91-degree peak early in the month to the chilly low of 51 degrees toward the tail.

Our outlook at the start of the month correctly called for a warm and dry month; however, we estimated temperatures to be 1 to 2 degrees above normal and it was just 0.3 degrees above the norm.

Looking at the year so far, 2022 is tracking very slightly cooler and drier than last year and very close to the recent 30-year normals.

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