Historic summer heat in the U.S.

Anyone familiar with The United States’ mountain ranges will understand the cluster of pale yellow and pale blue dots in northwestern Wyoming and Colorado. It makes sense that the country's coolest hottest summer days would appear in Rocky Mountain territory.

The country's hottest daytime highs (black dots) are in the Desert Southwest: Arizona, Nevada, and southern California, where elevation and latitude are relatively low and the landscape is arid—all of which favor hot temperatures.

Topography and latitude aren't the only influences on how hot a location has ever gotten. Otherwise, how would we explain that the hottest temperatures on record for many locations in Florida (our country's flattest, most southerly state) are cooler than many of the records set by its northerly neighbors? Daytime high temperatures in Florida are moderated by its location adjacent to two large bodies of water. So we see more orange dots (indicating record-high temperatures near 100 ˚F) in Florida, than we do in Georgia and South Carolina, where the red dots indicate record temperatures closer to 110 ˚F.

We can see a similar influence at play around the Great Lakes. Locations in North Dakota that are at the same latitude as stations in Michigan's Upper Peninsula have record temps that are much hotter.

This map shows only those stations from the first map where the record-high daily temperature was set in the past five summers (2019-2023). More dots appear west of the Mississippi than east in this time period. The large number of dots in the Pacific Northwest show the influence of a blistering  June 2021 heat wave , which kicked off the region’s  hottest summer on record . In other parts of the West, the years of record-high temperatures were more scattered.   

This map shows only those stations from the first map where the record-high daily temperature was set this summer (2023). The cluster of dots in western Texas shows the imprint left by a  June heat wave  that affected the Southern Plains. The ones around the Gulf show the influence of heat wave that broiled the area in late August, contributing to state-wide temperatures that were  much above average  in Texas and Alabama and record warm in Louisiana, Missisippi, and Florida.