With a notable exception overnight temperatures Thursday in the Philadelphia region dropped deep into the 20s, and in some places that got all the way to 19.

Not surprisingly the notable exception was the official measuring station at Philadelphia International Airport where the readings didn’t make it below 30.

By comparison, the low at the Chester County Airport was 25; 24 in Wilmington; 21 in Blue Bell, Montgomery County, Mount Holly, and at the Atlantic City International Airport; and 19 in Pottstown and Millville.

Overnight conditions were ideal for allowing daytime heat to soar in the space, with clear skies and no wind — except at the airport, said Sarah Johnson, a lead meteorologist at the National Weather Service in Mount Holly.

» READ MORE: Where is temperature measured in Philly, and why?

A persistent light breeze from the south, 5 to 10 mph, inhibited the “rational cooling,” she said, and the temperature bottomed out at 30. or almost no wind.

The renegade breeze might have been related to the airport’s proximity to the Delaware River, she said.

Under any conditions, the automated site at the airport is in a peculiar setting that can affect temperature readings. It is situated in an open area, near the river; a swamp; and heat-retaining buildings and runways that add the urban heat island effect.

» READ MORE: Why this deep South Jersey location is such a thermal outlier

Still, 30 was the lowest official reading in Philadelphia since March 1, during the pre-lockdown era. Looking ahead a week can be a perilous exercise, but it’s all but certain that we won’t have a White Thanksgiving.

Temperatures are forecast to rise into the 50s Thanksgiving Day, but “there is potentially a system coming through that could bring rain,” Johnson said.