August Heat Wave


The National Weather Service in Chanhassen issued an Excessive Heat Warning for Hennepin County from 11am August 22nd, 2023, until August 23th, 2023 at 11pm. Heat index values were expected to reach temperatures in excess of 105° F with little relief expected overnight, with temperatures forecasted to stay in the 70s. After the warning, there will be a heat advisory in effect until the 24th at 7pm.

As we highlighted in July, make sure to drink plenty of fluids, stay in cool buildings or in the shade, reschedule outdoor events, wear lightweight and loose fitting clothes, check up on your neighbors, and limit any physical activity outdoors. If you or someone you are with are experiencing symptoms of heat stroke, call 911 and seek medical attention immediately.


As a reminder: NEVER leave any person or pet in a unattended car. Temperatures rise very quickly inside vehicles in the heat, causing it to act as an oven and become life-threatening to anyone inside within minutes. Always check the back seat and make sure all passengers are out.


Collage of Hennepin West Mesonet maps showing air temperature, heat index, Wet Bulb Globe Temperature, and relative humidity from August 22, 2023.


The image above shows the conditions at 8:32am, 12.31pm, and 3:25pm on 8/22 to showcase the changes in the environment. In the morning, temperatures were in the upper 70s, with humidity readings in the upper 80s. As the day went on, the heat index strayed farther and farther away from the air temperature, with the heat index reading as high as 117 degrees F while the air temperature was in the mid to upper 90s. The humidity also decreased as the day progressed, still reading in the upper 50s to low 60s at the hottest time of the day. The high temperatures and relatively high humidity combined to produce such high heat index values and wet bulb globe temperatures.


This graphic was found on the Hennepin West Mesonet map with the current air temperature (first on the left), and the heat index (second from the left). Wet bulb globe temperature and then relative humidity follow. Heat index is the combination of heat and humidity, and outputs the temperature the body could experience. This can be found by going to the preconfigured dropdown, then "Extreme Heat", or for individual maps you can hit "Customized",  hit the "Temperature" category, and then select "Current Heat Index" and "Current Air Temperature" maps.