Another late-season freeze is expected Thursday in the Philly area
Temperatures outside the city may be 10 degrees chillier Thursday morning than they are at the airport.
The cherry blossoms and most other blooms evidently weathered the Wednesday morning freeze, but they may be in for another (maybe final) challenge Thursday as temperatures could drop into the mid-20s outside the city.
As was the case for Wednesday, the National Weather Service has posted a “freeze warning” for the entire region. However, the outcomes this go-round could be considerably different, said Ray Martin, a lead meteorologist in the Mount Holly office.
On Wednesday morning, it got down to 31 degrees at Philadelphia International Airport, the latest official “freeze” in four years, and 10 days later than the average last freeze in this century. Lows outside the city generally were in the 28-to-30 range.
Come Thursday morning, don’t be surprised if the difference between the city and the neighboring counties ends up being on the order of 10 degrees, said Martin.
The wind, or lack of it, will effect temperatures in the Philly region
Steady winds overnight that persisted past daybreak were factors in driving temperatures below freezing at the airport, Martin said.
In effect, they overpowered the urban heat lsland effect, generated by heat-holding structures and runways. To get to freezing at PHL this late in the season, he said, “You want something that’s gong to blow in the cold air from somewhere else.”
That won’t be the case early Thursday as the breezes die down. “When the wind goes away, the urban heat island will return with a vengeance,” he said.
The lack of wind will make it feel less harsh in the morning, but it also will allow temperatures to plummet in suburban and rural areas, he said, as they will allow daytime heat absorbed by the ground to radiate efficiently into space.
While the official weather service forecast calls for the airport to visit freezing again Thursday morning, Martin said he is skeptical.
He expects readings in the city to bottom out in the mid-30s, while being 10 degrees colder elsewhere.
That could put some stress on the blooms.
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Some magnolia blossoms did take a hit at Longwood Gardens, said spokesperson Patricia Evans, but the cherry blossoms and bulbs “are fine.”
Said Bill Cullina, executive director of the Morris Arboretum & Gardens of the University of Pennsylvania, in Chestnut Hill, where it tends to be considerably chillier than the airport, cherry blossoms and other flowering tees “usually” handle the mid-20s. So do ”early shrubs as well as spring bulbs like daffodils and tulips."
But if temperatures “drop much below that, we could see additional damage,” he said.
That is unlikely, and after Thursday, said Martin, it’s likely that the city will be done with freezes until sometime in the fall.