The Chelsea 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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78° on Nov. 15, 1993, the hottest reading for this week of the year since 1872. Next is 76° in 1909.
Chelsea’s center stands about 30 ft above sea level. Within three miles the land runs from 0 ft to 130 ft, a difference of 130 ft: gently rolling country. Open water lies within three miles. The highest named summit within 15 miles is Great Blue Hill, about 630 ft, 13 miles south-southwest.
Under the town center the state geologic map shows Cambridge Argillite, from the Neoproterozoic to Early Cambrian, 521 to 1,000 million years old.
The section below crosses 4 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 56×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Argillite. Age: Neoproterozoic to Early Cambrian, 521 to 1,000 million years old. About 8 mi of the line.
Diorite, gabbro. Age: Neoproterozoic, 542 to 1,000 million years old. About 4 mi of the line.
Metavolcanic. Age: Neoproterozoic, 542 to 1,000 million years old. About 1 mi of the line.
Granite, granodiorite. Age: Neoproterozoic, 615 to 645 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.
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 Chelsea reaches Boston Harbor and the Atlantic Ocean by way of the Mystic: about 1 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Chelsea; river miles along the main stem, rounded.
Chelsea has a hot-summer humid continental climate. Summer afternoons average 82° in July; winter nights fall to about 23° in January. A normal year brings about 49 inches of snow; with the rain, that comes to about 44 inches of water.
On November 14 Chelsea normally reaches 52° and falls to 38°. The record high is 71°, in 1993; the record low 16°, in 1905. The most rain on this date, 1.49 in, fell in 2009.
Normals 1991–2020 and records since 1872 from the Boston Area threaded record (Boston Logan International Airport, 3 miles south-southeast). NOAA, through RCC-ACIS.
