The O'Fallon plate. Relief from Copernicus GLO-30; rivers and lakes from USGS NHD; watersheds from the USGS Watershed Boundary Dataset; roads and city limits from Census TIGER 2024.
Sunny
Partly cloudy; warmer
Sunny
Sunny
Partly cloudy
Partly cloudy
Partly cloudy
4.19 inches of rain fell in two days, the most for this week of the year since records began in 1957. The next wettest, 2.96 inches, fell in 2003.
O'Fallon’s center stands about 550 ft above sea level. Within three miles the land runs from 430 ft to 640 ft, a difference of 210 ft: rolling country. The highest named summit within 15 miles is Tavern Rock, about 880 ft, 14 miles south-southwest.
The section below crosses 8 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 50×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Limestone. Age: Carboniferous, 324 to 359 million years old. About 8 mi of the line.
Limestone. Age: Carboniferous, 324 to 359 million years old. About 6 mi of the line.
Clay, silt, sand. Age: Holocene, less than 12,000 years old. About 5 mi of the line.
Limestone. Age: Middle Mississippian, 331 to 347 million years old. About 2 mi of the line.
Shale, sandstone. Age: Early Pennsylvanian to Middle Pennsylvanian, 307 to 324 million years old. About 1 mi of the line.
Shale, sandstone, coal. Age: Middle Pennsylvanian to Late Pennsylvanian, 304 to 315 million years old. About 1 mi of the line.
From the USGS State Geologic Map Compilation (Horton and others, 2017), the states’ geologic maps joined at a common scale. 2 smaller units along the line are not listed.
Heights from Copernicus GLO-90 (a surface model: it includes buildings and tree canopy); summits from USGS GNIS; rivers from USGS NHDPlus HR; rock from the USGS State Geologic Map Compilation.
A raindrop that lands in O'Fallon reaches the Gulf of America by way of Belleau Creek, Dardenne Creek and the Mississippi: about 1,220 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of O'Fallon; river miles along the main stem, rounded.
O'Fallon has a hot-summer humid continental climate. Summer afternoons average 88° in July; winter nights fall to about 21° in January. A normal year brings about 14 inches of snow; with the rain, that comes to about 44 inches of water.
On November 14 O'Fallon normally reaches 56° and falls to 35°. The record high is 80°, in 1989; the record low 10°, in 1986. The most rain on this date, 2.00 in, fell in 1993.
Normals 1991–2020 and records since 1957 at Weldon Spring Nws, 8 miles south. NOAA, through RCC-ACIS.
