The Helena 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
Partly cloudy; warmer
Mostly sunny
Partly cloudy
Mostly cloudy
Partly cloudy
Showers likely
74° on Nov. 13, 1999, the hottest reading for this week of the year since 1942. Next is 72° in 2012.
Helena’s center stands about 950 ft above sea level. Within three miles the land runs from 890 ft to 1,010 ft, a difference of 120 ft: gently rolling country.
Under the town center the state geologic map shows Upper Cambrian (sandstone, siltstone, shale), from the Cambrian, 487 to 497 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 42×. 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, siltstone, shale. Age: Cambrian, 487 to 497 million years old. About 22 mi of the line.
Sandstone, siltstone, shale. Age: Middle Cambrian to Cambrian, 487 to 521 million years old. About 2 mi of the line.
Dolostone, sandstone. Age: Early Ordovician, 471 to 487 million years old. About 0.8 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 Helena reaches the Gulf of America by way of the Raven Stream, Sand Creek, the Minnesota and the Mississippi: about 1,870 river miles.
Lake on the way: Lake Pepin.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Helena; river miles along the main stem, rounded.
Helena has a warm-summer humid continental climate. Summer afternoons average 81° in July; winter nights fall to about 5° 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 Helena normally reaches 42° and falls to 26°. The record high is 69°, in 1990; the record low −5°, in 1959. The most rain on this date, 1.23 in, fell in 2010.
Normals 1991–2020 and records since 1942 at Jordan 1 SSW, 5 miles north-northwest. NOAA, through RCC-ACIS.
