The Johnston 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
Mostly sunny
Mostly sunny
Partly cloudy
Mostly sunny
Showers likely
−3° on Nov. 12, 2019, the coldest reading for this week of the year since 1995. Next is 7° in 2005.
Johnston’s center stands about 830 ft above sea level. Within three miles the land runs from 790 ft to 980 ft, a difference of 190 ft: gently rolling country.
Under the town center the state geologic map shows Lower Cherokee Group and Raccoon Creek Group (shale, sandstone, siltstone), from the Early Pennsylvanian to Middle Pennsylvanian, 307 to 324 million years old.
The section below crosses 3 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 64×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Shale, sandstone, siltstone. Age: Early Pennsylvanian to Middle Pennsylvanian, 307 to 324 million years old. About 16 mi of the line.
Shale, siltstone. Age: Middle Pennsylvanian, 307 to 315 million years old. About 8 mi of the line.
Shale, limestone. Age: Middle Pennsylvanian, 307 to 315 million years old. About 0.1 mi of the line.
From the USGS State Geologic Map Compilation (Horton and others, 2017), the states’ geologic maps joined at a common scale.
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 Johnston reaches the Gulf of America by way of Beaver Creek, the Des Moines and the Mississippi: about 1,540 river miles.
Lake on the way: Roberts Creek.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Johnston; river miles along the main stem, rounded.
Johnston has a hot-summer humid continental climate. Summer afternoons average 85° in July; winter nights fall to about 13° in January. A normal year brings about 38 inches of snow; with the rain, that comes to about 36 inches of water.
On November 14 Johnston normally reaches 48° and falls to 30°. The record high is 75°, in 2025; the record low 7°, in 2014. The most rain on this date, 0.17 in, fell in 2008.
Normals 1991–2020 and records since 1995 at Des Moines Wsfo-Johnston, 5 miles north-northwest, 130 ft higher. NOAA, through RCC-ACIS.
