Twin Cities Superstorm: July 23-24, 1987 [View all]

Any resident over the age of 40 who lived in the Twin Cities remember where they were on July 23, 1987. The largest rainfall event in Twin Cities' history began in the late evening and within six hours, ten inches of rain fell at the Twin Cities International Airport, causing massive flooding especially in the southern and western parts of the metro.

https://www.dnr.state.mn.us/climate/journal/870723_24_superstorm.html

As of today, this was when the largest amount of rain fell in the airport.