A closer look at September weather in Washington, D.C.

 

A stellar evening at Nationals Park

The first half of September has featured no shortage of sunny and stellar weather in the nation’s capital. It’s also been a cooler than average month with nine of the first 13 days below average.

Washingtonians may have noticed the lack of extreme heat dating back to last month. That’s similar to last September that was also cooler than average in the nation’s capital. However, a key difference between last September and the first half of this September is the number of 90-degree days. September 2024 was DC’s first without any 90-degree heat since 2011. Meanwhile, this September 6 saw a sultry high of 93° at National Airport that was DC’s hottest September day in nearly two years.

Average daily high temperatures plummet throughout the month, from 85° on September 1, to 75° by month’s end. However, the nation’s capital has averaged between three and four September days of 90-degree heat over the last 30 years, according to NOAA data. Although NOAA’s Climate Prediction Center expects predominantly warmer than average weather for the D.C. Metropolitan Region over the next few weeks, no 90-degree heat is likely in the nation’s capital.

The nation’s capital averaged roughly two September days with highs in the 60s, dating back to the mid-1990s. For example, Washingtonians had four September days with highs in the 60s in 2020, but that was DC’s coolest September since 2009. Cooler than average September days with highs in the 60s can also be a function of heavy rain.

Beneficial rainfall would be excellent news for the nation’s capital this September. That’s because the latest Drought Monitor Index shows abnormally dry conditions have returned across much of D.C., Maryland and Virginia (DMV). A smaller area of moderate drought conditions exists within the abnormally dry conditions across the DMV.