O'Fallon, MO Weather Records Since April 2005
| Temperature | ||
| Highest Temperature | 107.3 °F | at 5:00 PM on 28 June 2012 |
| Highest Heat Index | 124.1 °F | at 6:28 PM on 02 August 2011 |
| Lowest Temperature | -8.8 °F | at 7:44 AM on 06 January 2014 |
| Lowest Windchill | -33.5 °F | at 8:26 AM on 06 January 2014 |
| Highest Minimum | 83.0 °F | at 6:09 AM on 24 July 2012 |
| Lowest Maximum | 1.9 °F | at 12:00 AM on 06 January 2014 |
| Rainfall | ||
| Highest Rain Rate | 52.36 in/hr | at 9:44 AM on 31 July 2021 |
| Highest Hourly Rain | 3.24 in | at 12:11 AM on 09 August 2020 |
| Highest Daily Rain | 4.19 in | on 25 June 2021 |
| Highest Monthly Rain | 12.03 in | October 2009 |
| Wind | ||
| Highest Gust | 58.0 mph | at 5:00 PM on 18 June 2012 |
| Highest Average | 26.0 mph | at 4:57 PM on 20 February 2014 |
| Pressure | ||
| Highest Pressure | 30.984 in | at 4:27 PM on 07 January 2015 |
| Lowest Pressure | 29.027 in | at 3:30 AM on 26 October 2010 |
| Page Updated | 8/4/2021 7:10:00 AM |