The Isabel 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.
Partly cloudy
Mostly sunny; warmer
Partly cloudy
Partly cloudy
Partly cloudy; cooler
Mostly cloudy
Chance of showers
78° on Nov. 12, 1999, the hottest reading for this week of the year since 1949. Next is 73° in 1975.
Isabel’s center stands about 2,400 ft above sea level. Within three miles the land runs from 2,260 ft to 2,430 ft, a difference of 170 ft: gently rolling country.
Under the town center the state geologic map shows Hell Creek Formation (shale), from the Late Cretaceous, 66 to 100 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 47×. 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. Age: Late Cretaceous, 66 to 100 million years old. About 16 mi of the line.
Sandstone, siltstone. Age: Late Cretaceous, 66 to 100 million years old. About 7 mi of the line.
Shale, bentonite. Age: Late Cretaceous, 66 to 100 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.
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 Isabel reaches the Gulf of America by way of Firesteel Creek, the Grand River, the Missouri and the Mississippi: about 2,500 river miles.
Lakes on the way: Lake Oahe, Lake Sharpe, Lake Francis Case and Lewis and Clark Lake.
1,170 miles of the trip are on the Mississippi.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Isabel; river miles along the main stem, rounded.
Isabel has a warm-summer humid continental climate. Summer afternoons average 84° in July; winter nights fall to about 7° in January. A normal year brings about 46 inches of snow; with the rain, that comes to about 19 inches of water.
On November 14 Isabel normally reaches 43° and falls to 21°. The record high is 73°, in 1975; the record low −17°, in 1959. The most rain on this date, 0.26 in, fell in 1956.
Normals 1991–2020 and records since 1949 at Glad Valley 2 W, 18 miles west. NOAA, through RCC-ACIS.
