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.
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3° on Nov. 16, 1933, the coldest reading for this week of the year since 1901. Next is 5° in 2019.
Helena’s center stands about 700 ft above sea level. Within three miles the land runs from 650 ft to 740 ft, a difference of 90 ft: gently rolling country.
Under the town center the state geologic map shows Lockport Dolomite (dolostone), from the Silurian, 425 to 445 million years old.
The section below crosses 2 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.
Dolostone. Age: Silurian, 425 to 445 million years old. About 21 mi of the line.
Dolostone. Age: Silurian, 428 to 445 million years old. About 3 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 Lake Erie by way of Muddy Creek: about 25 river miles. From there it moves on through the Great Lakes, over Niagara Falls and down the St. Lawrence to the Atlantic.
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 hot-summer humid continental climate. Summer afternoons average 85° in July; winter nights fall to about 18° in January. A normal year brings about 26 inches of snow; with the rain, that comes to about 38 inches of water.
On November 14 Helena normally reaches 51° and falls to 33°. The record high is 75°, in 1909; the record low 8°, in 2019. The most rain on this date, 1.52 in, fell in 1972.
Normals 1991–2020 and records since 1901 at Fremont, 9 miles east, 100 ft lower. NOAA, through RCC-ACIS.
