Excessive Heat — Polk, Wisconsin

2023-07-27 · Polk, Wisconsin

Event narrative

Warm environmental temperatures in the low to mid 90s combined with high dewpoint values reaching 80, caused high heat indices exceeding 105F for approximately four hours. The ASOS station located at the Osceola Municipal Airport recorded an apparent temperature of 114F at 2:15 PM (CST).

Wider weather episode

Surface temperatures reaching the mid to upper 90's combined with dew points in the 70s and lower 80s allowed for apparent temperatures, or the heat index, to exceed 105F in for multiple hours. Strong ridging aloft was in place over the southwestern U.S. which allowed for seasonally warm high temperatures to be carried east via zonal flow over the Central U.S.

In the lower levels, a surface low over the Dakotas along with transport of gulf moisture from the south allowed for dew point temperatures to remain elevated the night prior to July 27th, despite cloud cover lingering from prior convection over the northern plains. As clouds cleared the next day, daytime heating increased surface temperatures in an already humid air mass, causing heat indices to reach dangerous levels.

The highest heat indices from this event were:

New Richmond Regional Airport in St. Croix County: 115F

Osceola Municipal Airport in Polk County: 114F.

Source: NOAA Storm Events Database, event_id 1107184. Narrative written by the NWS forecast office that issued the report.