National Weather Service United States Department of Commerce


Intense heat and extremely high humidity levels lead to dangerously high heat indices on July 20, 2022. High temperatures in the mid to upper 90s combined with incredibly high dewpoints to produce heat index values ranging from 110 to 123. Cape Girardeau, MO tied their all-time highest heat index of 123 degrees, which was previously recorded on July 2, 1980. A weak frontal boundary moving into the region caused dewpoints to pool ahead of it. This resulted in a very tropical airmass with dewpoints rising into the upper 70s to lower 80s. A few sites even exceeded 82 degrees, which is very rare for our area.

Forecast Analysis

A mid level shortwave moved across the Great Lakes during the day which lead to a cold front moving into the Quad State during the late afternoon and evening. Abundant low level moisture pooled ahead of this boundary, resulting in ridiculously high humidity levels. Despite strong instability and plentiful moisture, only isolated thunderstorms formed ahead of the front. This was due to a strong cap (warm air aloft) in place along with weak wind shear. The thunderstorms that did develop struggled to maintain themselves and eventually fizzed out.

Surface Map - 7 AM July 20, 2022 Surface Map - 7 PM July 20, 2022
850mb Chart - 7 AM July 20, 2022 850mb Chart - 7 PM July 20, 2022
500mb Chart - 7 AM July 20, 2022  
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