DC Summer Weather Outlook: Hotter than normal dog days ahead?

WASHINGTON - Summer is upon us, and while the hot and humid summers are just a way of life in the D.C. region - some summers are worse than others. So, will this be more of an average summer, or a summer to remember? 

As with winter, the key often lies primarily with whether we are talking about a summer El Niño, or La Niña pattern. While the impacts of both are typically more pronounced in the winter, they can have significant impacts on summer precipitation patterns and the likelihood of heat waves as well. While it is not the only factor to consider in a summer outlook, it is often a starting point. 

After spending an entire winter in an El Niño regime, the waters in the equatorial Pacific have started to shift in a transition phase towards La Niña, which is expected to be in full swing by the end of the summer into next fall. 

What I term "Emerging La Niña" summers have a history of being on the hot side. An average summer here in D.C. features 33 days when the high temperature surpasses 90°F in the afternoon. The previous four summers when we were transitioning from an El Niño to a La Niña regime have exceeded this number, most recently in 2020 when D.C. recorded 46 days when high temperatures exceeded those years. 

In fact, the hottest summer on record here in D.C., 2012, featured 67 days above 90°F and was one of those transition years. So, we expect that this summer will be hotter than normal. It could even feature a few days above 100°F... which D.C. has not done since 2016.

A tougher call in rainfall and severe weather, La Niña summers are known for being abnormally dry, but these transition summers can be tricky. One thing we can look towards is the very warm Gulf of Mexico and southern Atlantic Ocean, typical source regions for moisture for our region. 

Water temperatures in these regions are already at levels more typical of middle to late summer. This likely means we are in for a very humid summer, which in turn would make the threat for summertime storms a little more likely throughout the course of the summer. 

In addition, an active tropical season could bring tropical remnants to our region, though this is more likely later in the summer and through the fall months. 

In conclusion, most of the indicators we examine are indicating that we are in for a hotter than normal summer ahead. We are forecasting 45–55 days above 90°F, along with 1-2 days above 100°, both well above normal for a summer in D.C. 

Due to higher-than-normal humidity, we are also expecting that the summer will have greater risks for storms and severe weather, compared to a typical summer.