Here is a summary of record highs as reported by the NWS
Waterloo 86 85(1931)
Moline, IL 86 83(1941)
Cedar Rapids 86 84(1931)
Spencer 88 84(1931)
Lamoni 87 80(1941)
Mason City 85 83(1931)
Ottumwa 87 86(1908)
Atlantic 88 86(1908)
Sioux City [1] 91 87(2003)
Des Moines 89 89(1883) TIED
St Joseph, MO 92 88(1936)
Rochester, MN 82 80(1941)
Mankato, MN 84 84(1985) TIED
Minneapolis, MN 84 78(1976)
[1] This was the fourth earliest date in the year for the
first 90 degree reading. The earliest date was
30 March 1968 for Sioux City.