An impressive glaze of white coated cars north and west of the city Friday morning, and some areas received their first serious frost of the season.
Officially, however, the temperature at Philadelphia International Airport didn't even get into the 30s, another case study for the urban heat island effect and the location of the thermometer, near the river and a swamp near the city's southwestern border.
After dark, temperatures between the city and the suburbs can vary by several degrees when the winds are light and the skies generally fair – as was the case during the overnight hours.
Those conditions allow daytime heat to radiate into space, but all those paved surfaces and buildings in the vicinity of the official thermometer can have a heat-trapping effect.
The Philadelphia low will flirt with freezing on Monday, and then the chill is due to ease.
As we've noted, during the last decade, the first freeze has been occurring around Nov. 13, on average.
By contrast, the long-term average for the 140 years of records would be about Nov. 8, but looking decade-by-decade, those first- freeze dates show tremendous variability.
For example, during the legendarily cold 1960s, the average date was Oct. 22. Official The freezing reading of Oct. 5, 1961, holds the record for the earliest.
In the legendarily warm 1930s, the average date was Nov. 20.