The Armstrong 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.
Mostly sunny
Partly cloudy; warmer
Mostly sunny
Partly cloudy
Partly cloudy
Mostly sunny
Showers likely
80° on Nov. 14, 1999, the hottest reading for this week of the year since 1954. Next is 75° in 2001.
Armstrong’s center stands about 1,240 ft above sea level. Within three miles the land runs from 1,200 ft to 1,280 ft, a difference of 80 ft: gently rolling country.
Under the town center the state geologic map shows Dakata and Windrow Formations (sandstone, shale), from the Early Cretaceous to Late Cretaceous, 94 to 113 million years old.
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.
Sandstone, shale. Age: Early Cretaceous to Late Cretaceous, 94 to 113 million years old. About 24 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 Armstrong reaches the Gulf of America by way of the Des Moines and the Mississippi: about 1,760 river miles.
Lakes on the way: Roberts Creek and Big Creek Pounding Area.
1,330 miles of the trip are on the Mississippi.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Armstrong; river miles along the main stem, rounded.
Armstrong has a warm-summer humid continental climate. Summer afternoons average 81° in July; winter nights fall to about 4° in January. A normal year brings about 40 inches of snow; with the rain, that comes to about 33 inches of water.
On November 14 Armstrong normally reaches 43° and falls to 23°. The record high is 80°, in 1999; the record low −10°, in 1959. The most rain on this date, 1.37 in, fell in 2010.
Normals 1991–2020 and records since 1954 at Swea City 5 N, 10 miles east-northeast. NOAA, through RCC-ACIS.
