The Potomac 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.
Sunny
Mostly sunny
Sunny
Partly cloudy
Mostly sunny
Partly cloudy
Partly cloudy
2° on Nov. 17, 1959, the coldest reading for this week of the year since 1887. Next is 3° in 2019.
Potomac’s center stands about 670 ft above sea level. Within three miles the land runs from 640 ft to 730 ft, a difference of 90 ft: gently rolling country.
Under the town center the state geologic map shows Carbondale Formation (shale, sandstone, coal), from the Middle Pennsylvanian to Late Pennsylvanian, 304 to 315 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 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.
Shale, sandstone, coal. Age: Middle Pennsylvanian to Late Pennsylvanian, 304 to 315 million years old. About 16 mi of the line.
Shale, sandstone. Age: Early Pennsylvanian to Middle Pennsylvanian, 307 to 324 million years old. About 5 mi of the line.
Siltstone. Age: Early Mississippian to Middle Mississippian, 331 to 359 million years old. About 2 mi of the line.
Shale, limestone. Age: Late Pennsylvanian, 304 to 307 million years old. About 0.6 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 Potomac reaches the Gulf of America by way of Bluegrass Creek, the Middle Fork Vermilion, the Vermilion, Big Bayou, the Wabash River Old Channel, the Old Channel Wabash, the Ohio and the Mississippi: about 1,400 river miles.
970 miles of the trip are on the Mississippi.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Potomac; river miles along the main stem, rounded.
Potomac 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 20 inches of snow; with the rain, that comes to about 41 inches of water.
On November 14 Potomac normally reaches 51° and falls to 34°. The record high is 74°, in 1971; the record low 10°, in 1940. The most rain on this date, 1.14 in, fell in 1972.
Normals 1991–2020 and records since 1887 at Hoopeston, 13 miles north-northeast. NOAA, through RCC-ACIS.
