Hot weather impacts people's health. Heat index is a combined measure of air temperature and relative humidity that indicates how hot it really feels. Many health agencies throughout the United States, with assistance from the National Weather Service, use heat index to communicate health risk due to hot weather.

  • Heat index by month

Monthly summer temperature, 2000-2022

In Minnesota, the monthly average heat index is lowest in May and highest in July. More Minnesotans are treated for heat-illness in the emergency department (ED) in July, when the heat index is the highest, compared to other summer months.

Source: National Aeronautics and Space Administration, North American Land Data Assimilation System (NLDAS), 2000-2022.

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    • Average heat index (County)
    • Extreme heat days (County)

    Average summer heat index in Minnesota by county, 2019-2022

    Heat index is a measure of the ambient temperature and humidity that estimates the "real feel" of the temperature outside.The map shows that the average heat index is higher in the southwestern and southeastern parts of Minnesota, as well as the 7-county metropolitan area. This corresponds with average higher temperatures in southern Minnesota versus northern Minnesota.

    Source: National Aeronautics and Space Administration, North American Land Data Assimilation System (NLDAS), 2019-2022. Average max daily heat index. The average summer heat index from 2019-2022 was determined by averaging the maximum daily heat index from May through September for the three years for each county.
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      Number of extreme heat days in Minnesota by county, 2022

      Extreme heat days were defined as days that had a heat index over the 95th percentile of the baseline (based on the daily heat index for the years 1991-2020). Every county in the state had at least five days of extreme heat in 2022, which shows that every Minnesotan is at risk for heat-related illness due to a high heat index. Generally there were more extreme heat days in the southwestern part of Minnesota. Even northern counties had days where the daily maximum was higher than the 95% threshold.

      Source: National Aeronautics and Space Administration, North American Land Data Assimilation System (NLDAS), 2022. Extreme heat days defined as days with max daily heat index over the 95th percentile relative threshold.
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