Freeze watches up for parts of Philly region, frost possible elsewhere, maybe even a few snowflakes
Patchy frost likely will be widespread, but the "heat island" effect will offer Philly a measure of protection.
A plant-threatening freeze is possible in parts of the region early Friday, and patchy frost is possible elsewhere.
The National Weather Service has posted a freeze watch for an umbrella of counties around the I-95 corridor.
In and around Philadelphia, the urban heat island effect, which inhibits overnight cooling, likely will keep temperatures above 32.
However, frost can form even at temperatures above freezing. Cold air sinks, and at ground level it can be colder than it is six to eight feet up, where temperature readings are taken.
With winds light, conditions will be favorable for daytime heating to radiate into space. Readings could drop below freezing north and west of the city.
And for Millville, N.J., and areas around the Pine Barrens, “it could be a solid freeze” early Friday, said Nicholas Carr, a meteorologist at the weather service’s Mount Holly office.
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Even a few snowflake sightings were reported on Thursday, when the forecast high, 50, would be about 15 degrees below long-term averages and normal for a Dec. 1.
The forecast low for Friday in the city is 34.
It isn’t easy getting to freezing in the city in mid-April, especially at the official observation station at Philadelphia International Airport, where the thermometer is located not far from buildings, runways, a swamp, and the Delaware River.
It did get to 27 degrees on April 17, 1943, the record for the date.
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However, not a single daily-low record has been set in April in Philadelphia since 1985; seven record daily highs have been recorded in April in the 21st century.