The Philadelphia 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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4.44 inches of rain fell in two days, the most for this week of the year since records began in 1903. The next wettest, 3.64 inches, fell in 1955.
Philadelphia’s center stands about 850 ft above sea level. Within three miles the land runs from 820 ft to 890 ft, a difference of 70 ft: gently rolling country.
Under the town center the state geologic map shows Muscatatuck Group (limestone, dolostone), from the Devonian, 359 to 422 million years old.
The section below crosses 3 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.
Limestone, dolostone. Age: Devonian, 359 to 422 million years old. About 23 mi of the line.
Limestone, dolostone. Age: Silurian, 422 to 445 million years old. About 1 mi of the line.
Black-shale. Age: Devonian to Carboniferous, 324 to 422 million years old. About 0.2 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 Philadelphia reaches the Gulf of America by way of Sugar Creek, the Driftwood, the Flatrock, the East Fork White, the White River, Big Bayou, the Wabash River Old Channel, the Old Channel Wabash, the Ohio and the Mississippi: about 1,480 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 Philadelphia; river miles along the main stem, rounded.
Philadelphia has a hot-summer humid continental climate. Summer afternoons average 84° in July; winter nights fall to about 19° in January. A normal year brings about 20 inches of snow; with the rain, that comes to about 48 inches of water.
On November 14 Philadelphia normally reaches 52° and falls to 33°. The record high is 74°, in 1955; the record low 6°, in 2019. The most rain on this date, 3.00 in, fell in 1993.
Normals 1991–2020 and records since 1903 at Greenfield, 4 miles east. NOAA, through RCC-ACIS.
