O'Fallon, Missouri climate: NOAA's gridded normals for the city, beside the nearest station records
NOAA's gridded 1991-2020 normals put O'Fallon's center at January lows of 22°F and July highs of 88°F, a yearly mean of 55.5°F and 42.8 inches of precipitation. No NOAA station keeps a record under the city's name. The nearest station record, Weldon Spring (6 miles S, 610 ft), has January lows of 21°F and July highs of 88°F.
95,355 people (Census Bureau 2024). Distances and directions are from the city's center.
- Jan 39° 22°
- Feb 45° 26°
- Mar 56° 34°
- Apr 67° 44°
- May 76° 55°
- Jun 84° 64°
- Jul 88° 68°
- Aug 87° 65°
- Sep 80° 57°
- Oct 69° 46°
- Nov 55° 35°
- Dec 44° 27°
Each month: normal high (large) and low, °F. Fill: the month's normal mean, colder blue to hotter red.
The months above are NOAA's gridded normals at O'Fallon's center.
What is each month like in O'Fallon?
NOAA's grid estimates the normals every 5 km or so from the stations around each point, terrain included. It smooths between stations, so night lows at the heart of a large city can run warmer than the grid shows: at five big-city airports we compared, the grid's highs were within about 1°F of the station and its lows 1-6°F cooler. The nearest record's high and low are beside each month.
| Month | High | Low | Mean | Precip. | Weldon Spring high | Weldon Spring low |
|---|---|---|---|---|---|---|
| January | 39°F | 22°F | 30.6°F | 2.52 | 39°F | 21°F |
| February | 45°F | 26°F | 35.3°F | 2.26 | 45°F | 24°F |
| March | 56°F | 34°F | 44.9°F | 3.57 | 55°F | 33°F |
| April | 67°F | 44°F | 55.6°F | 4.76 | 67°F | 44°F |
| May | 76°F | 55°F | 65.2°F | 5.03 | 76°F | 54°F |
| June | 84°F | 64°F | 74.0°F | 4.49 | 84°F | 63°F |
| July | 88°F | 68°F | 77.9°F | 3.77 | 88°F | 67°F |
| August | 87°F | 65°F | 76.2°F | 3.70 | 87°F | 65°F |
| September | 80°F | 57°F | 68.7°F | 3.38 | 80°F | 57°F |
| October | 69°F | 46°F | 57.2°F | 3.21 | 68°F | 46°F |
| November | 55°F | 35°F | 45.1°F | 3.46 | 55°F | 35°F |
| December | 44°F | 27°F | 35.0°F | 2.61 | 44°F | 26°F |
In metric: a yearly mean of 13.1°C, January lows of −6°C, July highs of 31°C and 1,086 mm of precipitation a year.
Source: NOAA NCEI U.S. Monthly Gridded Climate Normals 1991-2020 (nClimGrid, accession 0245564); NOAA NCEI 1991-2020 station normals. The grid cell holding the city's Census center point.
What do the station records around O'Fallon say?
Each row is a NOAA station's own 1991-2020 normals, with the snow and frost dates the grid does not give. A record downhill or nearer the coast than the city can run warmer, one uphill cooler: compare the elevations.
| Record | Where | Elevation | Year | Jan low | Jul high | Precip. | Snow | Last frost |
|---|---|---|---|---|---|---|---|---|
| Weldon SpringWeldon Spring NWS | 6 mi S | 610 ft | 55.2°F | 21°F | 88°F | 44.4 | 14 | April 10 |
| St. PetersSt Peters (2 mi SE) | 7 mi E | 575 ft | 55.3°F | 21°F | 88°F | 42.3 | 15 | April 9 |
| St Louis Spirit of St. Louis Airport | 9 mi S | 462 ft | 56.1°F | 22°F | 90°F | 39.8 | – | April 12 |
Source: NOAA NCEI 1991-2020 U.S. Climate Normals; place center and population: Census Bureau 2024. Last frost: the median last spring date of 32°F.
How much snow, how late a frost, what zone and how much sun in O'Fallon?
NOAA's grid gives no snow, frost dates or records, so these come from the nearest station record, Weldon Spring (6 miles S, 610 ft). It gets 14 inches of snow in a normal year. The last spring frost (32°F) comes after April 10 in half of years and the first autumn frost before October 26. Its record high is 109°F (2000) and its record low −23°F (1977) (kept since 1957).
The USDA's 2023 Plant Hardiness Zone Map puts O'Fallon in zone 6b across its 3 ZIP code areas.
Over a year 75% of the sunlight that would reach the ground under clear skies gets through the clouds in the area (4.2 kWh per square metre a day, NASA POWER 2001-2020); July is the sunniest month (82%) and December the cloudiest (66%).
Weldon Spring's page has its months, frost probabilities, records by month and recent years. NOAA's grid has monthly figures only, so there are no day-by-day month pages for O'Fallon; the nearest record's month pages have them.
Source: NOAA NCEI 1991-2020 normals, station USC00238805; records: ACIS; USDA 2023 Plant Hardiness Zone Map, ZIP listings: PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed October 8, 2026; sunshine: NASA POWER.
How does the climate vary across O'Fallon, ZIP code by ZIP code?
3 ZIP code areas lie wholly or partly in O'Fallon. On NOAA's grid 63366 is the warmest (55.5°F a year) and 63367 the coolest (55.4°F), so the city is nearly uniform. Each row also names the nearest station record and its frost dates.
| ZIP code | Zone | Year | Jan low | Jul high | Precip. | Nearest record | Last frost | First frost |
|---|---|---|---|---|---|---|---|---|
| 63366 | 6b | 55.5°F | 22°F | 88°F | 42.1 | St. Peters (10 mi) | April 9 | October 26 |
| 63367 | 6b | 55.4°F | 22°F | 88°F | 42.7 | Weldon Spring (8 mi) | April 10 | October 26 |
| 63368 | 6b | 55.5°F | 22°F | 88°F | 42.8 | Weldon Spring (4 mi) | April 10 | October 26 |
Source: Census Bureau 2020 ZCTA-to-place relationship file and ZCTA centers; NOAA NCEI gridded and station normals, 1991-2020. A ZIP area counts when at least a tenth of its land (and 0.5 km²) is in the city; its figures are the grid cell at its center; frost dates are the nearest record's medians of 32°F.