The Londonderry 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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74° on Nov. 11, 2024, the hottest reading for this week of the year since 1978. Next is 72° in 1993.
Londonderry’s center stands about 560 ft above sea level. Within three miles the land runs from 380 ft to 650 ft, a difference of 270 ft: rolling country. The highest named summit within 15 miles is Gap Hill, about 880 ft, 10 miles northwest.
Under the town center the state geologic map shows "Glenarm Wissahickon" formation (mica-schist), from the Paleozoic, 252 to 542 million years old.
The section below crosses 9 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 27×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Mica-schist. Age: Paleozoic, 252 to 542 million years old. About 12 mi of the line.
Mica-schist, quartzite. Age: Paleozoic, 252 to 542 million years old. About 3 mi of the line.
Gneiss. Age: Precambrian. About 2 mi of the line.
Gneiss. Age: Precambrian. About 2 mi of the line.
Schist, phyllite. Age: Paleozoic, 252 to 542 million years old. About 1 mi of the line.
Muscovite-schist. Age: Proterozoic, 542 to 2,500 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. 3 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 Londonderry reaches Delaware Bay and the Atlantic Ocean by way of Doe Run, Buck Run, West Branch Brandywine Creek, Brandywine Creek, the Christina and the Delaware: about 80 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Londonderry; river miles along the main stem, rounded.
Londonderry has a hot-summer humid continental climate. Summer afternoons average 85° in July; winter nights fall to about 22° in January. A normal year brings about 18 inches of snow; with the rain, that comes to about 48 inches of water.
On November 14 Londonderry normally reaches 54° and falls to 33°. The record high is 72°, in 1993; the record low 15°, in 2022. The most rain on this date, 0.92 in, fell in 1995.
Normals 1991–2020 and records since 1978 at Octoraro Lake, 10 miles west-southwest, 300 ft lower. NOAA, through RCC-ACIS.
