The Severn 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
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79° on Nov. 15, 1993, the hottest reading for this week of the year since 1950. Next is 77° in 1955.
Severn’s center stands about 170 ft above sea level. Within three miles the land runs from 90 ft to 300 ft, a difference of 210 ft: rolling country. The highest named summit within 15 miles is Chestnut Hill, about 610 ft, 12 miles north-northwest.
Under the town center the state geologic map shows Potomac Group, including Raritan and Patapsco Formations, Arundel Clay, and Patuxent Formation (sand), from the Cretaceous, 66 to 145 million years old.
The section below crosses 6 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 44×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Sand. Age: Cretaceous, 66 to 145 million years old. About 14 mi of the line.
Biotite-schist. Age: Proterozoic, 542 to 2,500 million years old. About 4 mi of the line.
Sand. Age: Cretaceous, 66 to 145 million years old. About 1 mi of the line.
Gabbro. Age: Proterozoic to Paleozoic, 252 to 2,500 million years old. About 1 mi of the line.
Fine-detrital, coarse-detrital. Age: Pleistocene, less than 2.6 million years old. About 0.9 mi of the line.
Quartz-monzonite. Age: Middle Ordovician to Late Devonian, 370 to 470 million years old. About 0.7 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 Severn reaches Chesapeake Bay and the Atlantic Ocean by way of Stony Run and the Patapsco: about 25 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Severn; river miles along the main stem, rounded.
Severn has a humid subtropical climate. Summer afternoons average 89° in July; winter nights fall to about 25° in January. A normal year brings about 19 inches of snow; with the rain, that comes to about 45 inches of water.
On November 14 Severn normally reaches 58° and falls to 37°. The record high is 77°, in 1989; the record low 18°, in 1986. The most rain on this date, 1.86 in, fell in 1972.
Normals 1991–2020 and records since 1950 at Baltimore-Washington International Airport, 3 miles north-northeast. NOAA, through RCC-ACIS.
