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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74° on Nov. 11, 2020, the hottest reading for this week of the year since 1893. Next is 71° in 2012.
Philadelphia’s center stands about 500 ft above sea level. Within three miles the land runs from 410 ft to 570 ft, a difference of 160 ft: gently rolling country. The highest named summit within 15 miles is Orvis Hill, about 1,070 ft, 12 miles south.
Under the town center the state geologic map shows Biotite and/or hornblende granite gneiss, from the Mesoproterozoic, 1 to 1.6 billion years old.
The section below crosses 11 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 36×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Unconsolidated. Age: Quaternary, less than 2.6 million years old. About 7 mi of the line.
Gneiss. Age: Mesoproterozoic, 1 to 1.6 billion years old. About 3 mi of the line.
Limestone. Age: Middle Ordovician, 459 to 471 million years old. About 3 mi of the line.
Paragneiss. Age: Mesoproterozoic, 1 to 1.6 billion years old. About 3 mi of the line.
Sandstone. Age: Cambrian, 487 to 497 million years old. About 2 mi of the line.
Gneiss. Age: Mesoproterozoic, 1 to 1.6 billion 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. 5 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 Philadelphia reaches the St. Lawrence River by way of the Indian, the Oswegatchie and the Saint Lawrence: about 120 river miles. The St. Lawrence carries it on to the Atlantic.
Lakes on the way: Lake Saint Lawrence and Black Lake.
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 warm-summer humid continental climate. Summer afternoons average 80° in July; winter nights fall to about 11° in January. A normal year brings about 116 inches of snow; with the rain, that comes to about 44 inches of water.
On November 14 Philadelphia normally reaches 47° and falls to 31°. The record high is 66°, in 2009; the record low 0°, in 2019. The most rain on this date, 0.76 in, fell in 1936.
Normals 1991–2020 and records since 1893 at Watertown, 15 miles southwest. NOAA, through RCC-ACIS.
