O'Fallon weather by month
Measured at St Louis/Spirit of St Louis Arpt
Averages and records for each calendar month at St Louis/Spirit of St Louis Arpt, United States, from 1987 to 2026. The warmest month is July, averaging 31.7°C; the coolest is January at 5.2°C.
| Month | Avg high | Avg low | Record high | Record low | Years |
|---|---|---|---|---|---|
| January | 5.2°C | −5.4°C | 24.4°C28 January 2002 | −26.7°C5 January 1999 | 36 / 36 |
| February | 7.8°C | −3.9°C | 28.9°C27 February 2024 | −24.3°C7 February 2014 | 37 / 37 |
| March | 14.4°C | 1.7°C | 34.4°C26 March 2026 | −17.2°C4 March 2002 | 37 / 37 |
| April | 20.3°C | 7.0°C | 34.4°C18 April 2002 | −6.1°C7 April 1990 | 36 / 36 |
| May | 24.9°C | 12.6°C | 35.0°C26 May 2012 | −0.6°C6 May 1992 | 37 / 37 |
| June | 29.9°C | 17.6°C | 42.8°C28 June 2012 | 7.2°C10 June 1988 | 37 / 37 |
| July | 31.7°C | 20.1°C | 42.2°C7 July 2012 | 10.0°C28 July 2013 | 37 / 37 |
| August | 31.0°C | 18.7°C | 41.1°C15 August 2007 | 7.8°C13 August 2004 | 36 / 36 |
| September | 27.4°C | 13.7°C | 38.9°C5 September 2026 | 0.0°C24 September 1989 | 35 / 37 |
| October | 20.7°C | 7.1°C | 34.4°C3 October 2006 | −4.9°C25 October 2013 | 36 / 36 |
| November | 13.9°C | 1.5°C | 29.4°C11 November 1989 | −15.0°C8 November 1991 | 36 / 36 |
| December | 7.4°C | −3.3°C | 25.0°C28 December 2025 | −30.0°C23 December 1989 | 36 / 36 |
Years shows the number behind the average high, then the number holding a record for that month. They differ because a year contributes an average only when the month has at least 25 days of readings, while a single reading is enough to set a record. The average low is withheld on the same 25-day rule and is counted separately again; it is shown as a dash where the archive cannot support it. Across the twelve months here the averages rest on 35 to 37 years each.
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Climate at nearby stations
The closest stations with twelve months of archive of their own, nearest first.
Every figure on this page is computed from NOAA GHCN-Daily observations stored per station, per year, per month. Nothing is modelled, interpolated or estimated, and a month the archive never covered is left out rather than filled in. A station appears here only once all twelve months carry an average from at least 10 years. See how this is built.