Frost dates for O'Fallon, Missouri
Missouri · first & last freeze, from NOAA 1991–2020 climate normals
In a typical year, the last spring freeze around O'Fallon comes near April 10 and the first fall freeze near October 26. One year in ten, a freeze still arrives after April 26 in spring — and one year in ten, the first fall freeze has already landed by October 12. NCEI's own growing-season statistic (days between freezes, percentiled per year) puts the median at 199 days.
Freeze-date probabilities, three thresholds
| Threshold | Last spring — 9 in 10 years past by | Last spring — typical (median) | Last spring — 1 in 10 years later than | First fall — 1 in 10 years by | First fall — typical (median) | First fall — 9 in 10 years by |
|---|---|---|---|---|---|---|
| 36°F — near-freezing (frost can occur) | April 8 | April 22 | May 6 | October 1 | October 16 | October 28 |
| 32°F — freezing | March 26 | April 10 | April 26 | October 12 | October 26 | November 8 |
| 28°F — hard freeze | March 12 | March 31 | April 15 | October 22 | November 5 | November 22 |
Measured at Weldon Spring Nws, MO (USC00238805), 6.3 mi from the city's census reference point, elev. 610 ft. NOAA/NCEI 1991–2020 normals. Read each date column as odds over the 30-year record — e.g. "9 in 10 years past by" means only one spring in ten saw a later freeze than that date.
Frost-free windows (computed)
| Window (32°F ends) | Opens | Closes | Length |
|---|---|---|---|
| Cautious (1-in-10 freeze risk at each end) | April 26 | October 12 | 169 days |
| Typical (median freeze dates) | April 10 | October 26 | 199 days |
| Gambler's (9-in-10 freeze risk at each end) | March 26 | November 8 | 227 days |
Pure arithmetic on the freeze-date percentiles above — the "cautious" window opens on the date only 1 year in 10 still sees a later spring freeze, and closes on the date by which only 1 year in 10 has already frozen.
About this city's numbers
- Census entity: O'Fallon city, Missouri — official 2024 population estimate 95,355.
- Weather station: Weldon Spring Nws, MO (USC00238805), 6.3 mi from the city's census-gazetteer reference point at elevation 610 ft. Frost dates are that station's history — neighborhoods vary.
- Data pulled 2026-09-05; normals period 1991-2020 (replaced by NOAA roughly once a decade).
More Missouri cities
Kansas City · St. Louis · Springfield · Columbia · Independence · Lee's Summit · all of Missouri →