The Byrnes Mill 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
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10° on Nov. 12, 2019, the coldest reading for this week of the year since 1987. Next is 13° in 2018.
Byrnes Mill’s center stands about 570 ft above sea level. Within three miles the land runs from 440 ft to 930 ft, a difference of 490 ft: hilly country. The highest named summit within 15 miles is Frisco Hill, about 860 ft, 7 miles east-southeast.
The section below crosses 6 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 36×. 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 6 mi of the line.
Limestone. Age: Carboniferous, 324 to 359 million years old. About 5 mi of the line.
Dolostone, limestone, shale. Age: Middle Ordovician, 459 to 471 million years old. About 5 mi of the line.
Dolostone. Age: Early Ordovician, 471 to 487 million years old. About 4 mi of the line.
Limestone. Age: Middle Ordovician, 459 to 471 million years old. About 3 mi of the line.
Dolostone, sandstone, limestone. Age: Early Ordovician to Middle Ordovician, 459 to 487 million years old. About 2 mi of the line.
From the USGS State Geologic Map Compilation (Horton and others, 2017), the states’ geologic maps joined at a common scale.
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 Byrnes Mill reaches the Gulf of America by way of the Big River, the Meramec and the Mississippi: about 1,180 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Byrnes Mill; river miles along the main stem, rounded.
Byrnes Mill has a hot-summer humid continental climate. Summer afternoons average 90° in July; winter nights fall to about 22° in January. About 40 inches of rain fall in a normal year.
On November 14 Byrnes Mill normally reaches 57° and falls to 35°. The record high is 80°, in 2025; the record low 13°, in 2018. The most rain on this date, 2.08 in, fell in 1993.
Normals 1991–2020 and records since 1987 at St Louis Spirit Of St Louis Airport, 16 miles north-northwest, 110 ft lower. NOAA, through RCC-ACIS.
