The Derry 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.
Mostly cloudy
Partly cloudy; warmer
Partly cloudy
Sunny
Sunny
Mostly sunny
Mostly sunny
76° on Nov. 15, 1973, the hottest reading for this week of the year since 1888. Next is 76° in 1993.
Derry’s center stands about 450 ft above sea level. Within three miles the land runs from 330 ft to 780 ft, a difference of 450 ft: hilly country. The highest named summit within 15 miles is Stony Mountain, about 1,710 ft, 13 miles north-northwest.
Under the town center the state geologic map shows Stonehenge Formation (limestone), from the Ordovician, 445 to 487 million years old.
The section below crosses 13 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 22×. 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. Age: Ordovician, 445 to 487 million years old. About 7 mi of the line.
Siltstone-mudstone, shale. Age: Triassic, 202 to 252 million years old. About 7 mi of the line.
Arkose. Age: Triassic, 202 to 252 million years old. About 3 mi of the line.
Limestone, dolostone. Age: Ordovician, 445 to 487 million years old. About 2 mi of the line.
Basalt. Age: Jurassic, 145 to 202 million years old. About 1 mi of the line.
Graywacke. Age: Ordovician, 445 to 487 million years old. About 1 mi of the line.
From the USGS State Geologic Map Compilation (Horton and others, 2017), the states’ geologic maps joined at a common scale. 7 smaller units along the line are not listed.
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 Derry reaches Chesapeake Bay and the Atlantic Ocean by way of Spring Creek, Swatara Creek and the Susquehanna: about 80 river miles.
Lake on the way: Lake Aldred.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Derry; river miles along the main stem, rounded.
Derry has a hot-summer humid continental climate. Summer afternoons average 87° in July; winter nights fall to about 23° in January. A normal year brings about 30 inches of snow; with the rain, that comes to about 44 inches of water.
On November 14 Derry normally reaches 54° and falls to 36°. The record high is 74°, in 1989; the record low 19°, in 1986. The most rain on this date, 1.74 in, fell in 1995.
Normals 1991–2020 and records since 1888 from the Middletown-Harrisburg Area threaded record (Middletown Harrisburg Int'L Airport, 8 miles southwest, 150 ft lower). NOAA, through RCC-ACIS.
