The Irwin 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.
Chance of showers
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78° on Nov. 12, 2010, the hottest reading for this week of the year since 1949. Next is 75° in 2009.
Irwin’s center stands about 1,450 ft above sea level. Within three miles the land runs from 1,300 ft to 1,570 ft, a difference of 270 ft: rolling country.
Under the town center the state geologic map shows Allegheny Formation (sandstone), from the Carboniferous, 299 to 324 million years old.
The section below crosses 4 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 29×. 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. Age: Carboniferous, 299 to 324 million years old. About 11 mi of the line.
Sandstone, conglomerate. Age: Carboniferous, 299 to 324 million years old. About 11 mi of the line.
Sandstone. Age: Carboniferous, 324 to 359 million years old. About 1 mi of the line.
Siltstone, shale. Age: Carboniferous, 324 to 359 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 Irwin reaches the Gulf of America by way of Scrubgrass Creek, the Allegheny, the Ohio and the Mississippi: about 2,060 river miles.
970 miles of the trip are on the Ohio.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Irwin; river miles along the main stem, rounded.
Irwin has a warm-summer humid continental climate. Summer afternoons average 81° in July; winter nights fall to about 17° in January. About 45 inches of rain fall in a normal year.
On November 14 Irwin normally reaches 50° and falls to 31°. The record high is 75°, in 2009; the record low 8°, in 1986. The most rain on this date, 1.15 in, fell in 1972.
Normals 1991–2020 and records since 1949 at Slippery Rock 1 SSW, 13 miles south-southwest, 190 ft lower. NOAA, through RCC-ACIS.
