DC’s rainy end to September

 

A September day in NW Washington, D.C.

This month’s weather in the nation’s capital stands out more than many recent Septembers. It has featured no shortage of cooler than average weather and is coming to a damp and wet conclusion. Despite the cloudy and wet weather over the past week, this month will still finish as drier than average month.

September is DC’s fourth rainiest month of the year with a monthly average of 3.93”, according to NOAA. Despite the gloomy weather of the last week, this month will finish with less than 3” of rain. That will make this the third consecutive drier than average September in Washington, D.C.

Oddly enough, this month will also finish with near average temperatures despite being the fourth warmest month of the year on average. Nine of the first 10 days of September were cooler than average and DC’s temperature average has remained below average for much of the month since then. This September will finish as DC’s first without any 90-degree heat since 2011. That’s in contrast to recent Septembers such as 2019 that featured nine days of 90-degree heat and last September that featured five consecutive days in the upper 90s.

In recent decades, cooler than average September’s have largely been a function of above average rainfall in the nation’s capital such as in 1999, 2011 and 2020. However, this month will finish with below average rainfall despite the gloomy weather over the last week. The DMV could actually use some beneficial rainfall, especially areas west of I-95 where drought conditions remain in effect. 

The cooler than average temperatures this month have been a relief to many following DC’s third hottest summer. The 2024 summer was not only very hot, it was also quite dry and that acerbated the drought conditions, particularly in areas along and west of I-81. That will be significant as the leaves start to change color. Traditionally, the autumn colors are more muted following a hot and dry summer.