O'Fallon, MO Weather Forecast
St. Charles County, Missouri
Seven-day outlook
42–81°F across the weekThe week runs between 54° and 80°, with today the warmest day of it. There is no real trend across it: one day looks much like the next. Tuesday is the wettest day, peaking near 59%. 3 of the 7 days stay dry.
Forecasts come from the National Weather Service's own computer models, and current conditions from the nearest reporting weather station. Both are served through the weather API. A forecast is guidance, not a warning, and anything the Weather Service has actually issued is on the live map.
The written summaries on this page are generated from the forecast data above, not by a meteorologist. Each sentence is a reading of the same numbers you can see, and no forecaster has reviewed them.
About the O'Fallon forecast
O'Fallon sits at 38.7847°N, 90.7207°W in St. Charles County, Missouri. The forecast above is drawn for that point from the National Weather Service's own computer models: a seven-day outlook, and a finer-grained one covering the next eighteen hours where it reaches, and the radar and alert panels show what the Weather Service has out over the area right now.
- County
- St. Charles County
- Coordinates
- 38.7847°N, 90.7207°W
- Population
- 94,074 · 2023 estimate
- Land area
- 30.525 sq mi
Place data from the US Census Bureau. Coordinates are the Census internal point for O'Fallon, and the forecast is for that location, not for every address inside the city limits, and a large city can have real weather differences from one side to the other.
How well can the network see O'Fallon?
The nearest Doppler radar is KLSX (St. Louis, MO), 6.3 miles to the SSE. A WSR-88D's lowest routine scan sits half a degree above horizontal, and the earth curves away beneath it, so by the time that beam reaches O'Fallon its center is about 310 ft above ground. That is about as close as radar coverage gets in the United States: the lowest scan is still near the ground when it reaches O'Fallon, so low-level rotation and the leading edge of a gust front show up on it. O'Fallon is closer to its radar than 98% of US cities.
The closest instrument actually measuring the air is KSUS · St Louis/Spirit of St Louis Arpt on the ASOS/AWOS network, 9.5 miles away. Near enough to be representative on most days, though a summer thunderstorm can soak one and miss the other entirely.
Beam height is the standard 4/3-earth approximation for the 0.5° scan and assumes normal refraction; it is where the center of the beam is, not its edges, and unusual temperature profiles bend it. Radar siting from the NWS WSR-88D network, station positions from the Missouri observing network as of this build.
Forecasts near O'Fallon
- Dardenne Prairie, MO3 mi
- Lake St. Louis, MO4 mi
- Cottleville, MO4 mi
- St. Paul, MO5 mi
- St. Peters, MO6 mi
- Weldon Spring, MO6 mi
- Wentzville, MO8 mi
- St. Charles, MO11 mi
Elsewhere in Missouri
Kansas CitySt. LouisSpringfieldColumbiaIndependenceLee's SummitAll Missouri forecasts →