OFallon Missouri Weather

OFallon - Weather Data from OFallon, MO

Latitude: N 38° 50' 20" Longitude: W 90° 43' 42" Altitude: 532 ft

CDT UTC Last station update CDT

WXSIM Forecast for: O'Fallon
Issued by: OFallonweather.com

Updated: Saturday, 15-Aug-2026 04:00 pm

Tonight Chance rain	Sunday Rain likely	Sunday night Rain likely	Monday Fog a.m.	Monday night Fog late	Tuesday Fog a.m.	Tuesday night Rain likely	Wednesday Chance rain
<.1 in.	<.25 in.	<.25 in.	<.1 in.			.35 in.	<.1 in.
Low: 77°	High: 89°	Low: 73°	High: 86°	Low: 69°	High: 89°	Low: 71°	High: 87°
	Heat: 99°				Heat: 95°		Heat: 92°
SW 4-17 mph	W 5-20 mph	NNW 5-16 mph	NNW 5-23 mph	N→ENE 2-19 mph	S→NW 3-21 mph	ESE→S 3 mph	NNE 4-21 mph
	UV: 8 Very High		UV: 8 Very High		UV: 8 Very High		UV: 8 Very High

Tonight	Partly cloudy in the evening, becoming mostly cloudy after midnight. Patchy light fog in the evening, then light to moderate fog after midnight. A chance of rain. Precipitation showery or intermittent. Warm. Low 77°. Wind southwest around 4 mph, gusting to 17 mph. Chance of precipitation 50 percent. Precipitation mostly less than a tenth of an inch.
Sunday	Partly cloudy. Light to moderate fog in the morning. Rain likely. Precipitation showery or intermittent. Hot. High 89°. Heat index up to 99°. UV index up to 8. Wind west around 5 mph, gusting to 20 mph. Chance of precipitation 70 percent. Precipitation mostly less than a quarter of an inch.
Sunday night	Partly cloudy. Moderate fog. Rain likely. Precipitation showery or intermittent. Low 73°. Wind north-northwest around 5 mph, gusting to 16 mph. Chance of precipitation 60 percent. Precipitation mostly less than a quarter of an inch.
Monday	Partly to mostly sunny in the morning, becoming mostly sunny in the afternoon. Moderate to dense fog in the morning. A chance of rain. High 86°. UV index up to 8. Wind north-northwest around 5 mph, gusting to 23 mph. Chance of precipitation 30 percent. Precipitation mostly less than a tenth of an inch.
Monday night	Clear in the evening, becoming fair after midnight. Light to moderate fog after midnight. Low 69°. Wind north around 2 mph, gusting to 19 mph, in the evening, becoming east-northeast after midnight.
Tuesday	Sunny. Light to moderate fog in the morning. Hot. High 89°. Heat index up to 95°. UV index up to 8. Wind south around 3 mph, gusting to 21 mph, in the morning, becoming northwest in the afternoon.
Tuesday night	Fair in the evening, becoming partly to mostly cloudy after midnight. Moderate fog after midnight. A chance of rain in the evening, then rain likely after midnight. Low 71°. Wind east-southeast around 3 mph in the evening, becoming south after midnight. Chance of precipitation 70 percent. Precipitation mostly between a quarter and half an inch.
Wednesday	Partly to mostly cloudy in the morning, becoming partly cloudy in the afternoon. Moderate fog in the morning. A chance of rain. Precipitation showery or intermittent. High 87°. Heat index up to 92°. UV index up to 8. Wind north-northeast around 4 mph, gusting to 21 mph. Chance of precipitation 50 percent. Precipitation mostly less than a tenth of an inch.
Wednesday night	Mostly cloudy in the evening, becoming cloudy after midnight. Light to moderate fog after midnight. A chance of rain in the evening, then rain likely after midnight. Precipitation showery or intermittent. Low 70°. Wind northeast around 5 mph, gusting to 18 mph, in the evening, becoming east after midnight. Chance of precipitation 90 percent. Precipitation mostly around half an inch.
Thursday	Cloudy in the morning, becoming mostly cloudy to cloudy in the afternoon. Light to moderate fog in the morning. Rain likely in the morning, then a chance of rain in the afternoon. Precipitation showery or intermittent. High 80°. UV index up to 5. Wind east around 4 mph, gusting to 19 mph. Chance of precipitation 70 percent. Precipitation mostly around a quarter of an inch.
Thursday night	Mostly cloudy in the evening, becoming partly cloudy after midnight. Patchy light fog in the evening, then moderate fog after midnight. Rain likely. Precipitation showery or intermittent. Low 69°. Wind east-northeast around 4 mph, gusting to 16 mph. Chance of precipitation 60 percent. Precipitation mostly around a tenth of an inch.
Friday	Partly to mostly cloudy in the morning, becoming partly to mostly sunny in the afternoon. Light to moderate fog in the morning. High 84°. UV index up to 8. Wind north around 7 mph, gusting to 25 mph.
Friday night	Mostly clear in the evening, becoming clear after midnight. Moderate fog after midnight. Low 65°. Wind north-northeast around 5 mph, gusting to 21 mph.

WXSIM forecast formatting script by Saratoga-Weather.org.

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