A large dome of high pressure that was centered across the mid section of the nation the week of July 18th, caused temperatures to rise into the 80s and 90s across the state. These temperatures combined with very high dew points in the mid to upper 70s, created heat indices between 100-110 degrees during the afternoon of Wednesday July 20th, and into Friday afternoon, July 22nd over portions of west central Wisconsin.
A frontal boundary aiding in pooling of dew points and associated higher heat indices during this time period, especially along the St. Croix and Mississippi River Valley.
The highest heat indices occurred between 12 noon and 7 pm. However, even the overnight temperatures only fell into the upper 70s to lower 80s, creating dangerous readings for those who did not have air conditioning or were caught out in the elements.
The following are recorded highest heat indices in this three day period;
Near Hudson 110 degrees
Spring Valley 110 degrees.

Excessive Heat in POLK, WISCONSIN
From 20-JUL-16 13:00:00 to 21-JUL-16 19:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Several surface observations across Polk County measured heat indices over 105 degrees for several hours during the afternoon of Wednesday, July 20th, and again Thursday afternoon July 21st. Temperatures only managed to fall into the mid to upper 70s during the morning of July 21st, and rebounded into the 80s and 90s once again by the afternoon. The highest heat index was 108 degrees along the St. Croix River.

Excessive Heat in PIERCE, WISCONSIN
From 20-JUL-16 13:00:00 to 21-JUL-16 19:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Several surface observations across Pierce County measured heat indices over 105 degrees for several hours during the afternoon of Wednesday, July 20th, and again Thursday afternoon July 21st. Temperatures only managed to fall into the mid to upper 70s during the morning of July 21st, and rebounded into the 80s and 90s once again by the afternoon. The highest heat index was 110 degrees along the Mississippi River.

Excessive Heat in ST. CROIX, WISCONSIN
From 20-JUL-16 13:00:00 to 21-JUL-16 19:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Several surface observations across St. Croix County measured heat indices over 105 degrees for several hours during the afternoon of Wednesday, July 20th, and again Thursday afternoon July 21st. Temperatures only managed to fall into the mid to upper 70s during the morning of July 21st, and rebounded into the 80s and 90s once again by the afternoon. The highest heat index was 110 degrees along the St. Croix River.

Excessive Heat in PEPIN, WISCONSIN
From 21-JUL-16 13:00:00 to 22-JUL-16 19:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Several surface observations across Pepin County measured heat indices over 105 degrees for several hours during the afternoon of Thursday, July 21th, and again Friday afternoon July 22nd. Temperatures only managed to fall into the mid to upper 70s during the morning of July 22nd, and rebounded into the 80s and 90s once again by the afternoon. The highest heat index value was 110 degrees along the Mississippi River.

Excessive Heat in EAU CLAIRE, WISCONSIN
From 21-JUL-16 13:00:00 to 22-JUL-16 19:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Several surface observations across Eau Claire County measured heat indices over 105 degrees for several hours during the afternoon of Thursday, July 21th, and again Friday afternoon July 22nd. Temperatures only managed to fall into the mid to upper 70s during the morning of July 22nd, and rebounded into the 80s and 90s once again by the afternoon. The highest heat index value was 109 degrees.

Excessive Heat in DUNN, WISCONSIN
From 20-JUL-16 13:00:00 to 21-JUL-16 19:00:00 (CST-6)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Several surface observations across Dunn County measured heat indices over 105 degrees for several hours during the afternoon of Wednesday, July 20th, and again Thursday afternoon July 21st. Temperatures only managed to fall into the mid to upper 70s during the morning of July 21st, and rebounded into the 80s and 90s once again by the afternoon. The highest heat index was 107 degrees.