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Hottest Days Coming Earlier

By Climate Central

With Memorial Day and the unofficial summer vacation season just around the corner, summer heat will soon begin to settle in. After a phenomenally warm February for much of the country, many of you have been asking us to take a look at how much earlier in the year the first occurrence of summer-like high temperatures are arriving.

First day with summer-like temperatures coming earlier

This week, we examine how early in the year certain threshold high temperatures first occurred in these cities. While we found a large variation from place to place, the vast majority of our stations analyzed (78 percent) had the first occurrence of a threshold high temperature trending earlier in the year. Some of the strongest trends were found in California, Florida, and the Great Lakes. Compared to 1970:

  • San Diego and San Francisco are seeing their first occurrence of 80°F about a month earlier.
  • Orlando and Tampa are seeing their first occurrence of 90°F about a week earlier. Miami’s first occurrence of 90°F is about a month earlier.
  • Detroit, Erie, Grand Rapids, Milwaukee, and Saginaw are all seeing their first occurrence of 80°F about 2-3 weeks earlier.

There are a handful of places, generally in the Carolinas and Georgia, where the first occurrence of 90°F is actually coming about 1-2 weeks later.

Methodology: To determine each city's threshold temperature, we examined the frequency of  maximum temperatures, in increments of 10°F, between 70-110°F, for each city. The threshold temperature for each city was chosen at the highest of these increments occurring at least 15 times per year.