Warmest on record at MSP by 2.4 degrees
2nd warmest at Milwaukee and Green Bay, WI (1925)
5th warmest at Madison, WI (warmest since 1963)
Warmest at La Crosse, WI by nearly 2 degrees
Warmest at Duluth, MN by 2.7 degrees
All of these periods of record date back to the 1800s. The last two entries on this list I would imagine are significantly less prone to UHI than the others, and they completely rewrote the record books by a huge margin. It’s not all UHI, and I would argue it’s not even primarily UHI.