Frost is possible on the anniversary of Philly’s earliest snowfall
On Oct. 10, 1979, officially 2.1 inches of snow were measured in Philadelphia
It won’t be snowing, but frost is possible in areas just outside the city Friday morning on the anniversary of Philadelphia’s earliest snowfall.
Temperatures are forecast to fall into the mid-30s in Philly’s surrounding counties. While that’s not close to freezing, it may be a scraping situation as the atmosphere leaves a wafer-thin coating of white on car roofs, windshields, lawns, and leaves.
The National Weather Service in Mount Holly has issued frost advisories, in effect from 2 to 9 a.m. Friday, for the entire region, save for Philadelphia and Delaware County, where urban heating is expected to hold off a visit from Emily Dickinson’s “blonde assassin.”
Frost is possible at temperatures above freezing
Although frost formation is tied to a variety of factors, in general it can form with readings as high as 36 degrees, said Sarah Johnson, warning coordination meteorologist in the Mount Holly office.
The air temperatures are taken about 6 feet off the ground, but they can be several degrees lower on the ground and on cooler surfaces.
“The key thing is clear skies and light or calm winds,” Johnson said, and that will be the case early Friday.
Temperatures should climb into the mid-60s Friday afternoon, and lows Saturday morning will be mostly in the 40s.
When will Philly have its first freeze?
Conditions during the weekend are forecast to deteriorate, with a chance of showers Saturday afternoon, and potentially it could be quite stormy Sunday into Monday, especially at the Shore.
However, no frost or freeze threats are in the extended outlooks, and if trends hold, Philly may have to wait a month before it sees a 32-degree reading, at least officially.
On average that first-freeze reading has been recorded in Pottstown on Oct. 21; Millville, Oct. 22; and Doylestown, Oct. 25 — and not until Nov. 11 at toasty Philadelphia International Airport, said Johnson’s colleague Ray Martin.
It really did snow once on Oct. 10 in Philly
Philadelphia’s first official freeze did not occur until Nov. 16 in 1979. Yet, that year on Oct. 10, it experienced its earliest first measurable snow in records dating to the late 19th century.
Officially, 2.1 inches was measured at Philadelphia International Airport. Yes, snow can accumulate on the cold ground when it’s above freezing.
Also on that date, the first-pitch temperature in Game 1 of the World Series between the Pittsburgh Pirates and Orioles in Baltimore was 41 degrees. At the time, it was a record low for the start of a World Series game.
The series was supposed to have begun on Oct. 9, but a wintry mix forced a postponement.