After what has been an unseasonably warm start to October across much of the northeast, some cold air is finally appearing on the horizon. After a couple of chilly mornings early this week, it appears the first widespread frost will come for northern and western Pennsylvania this weekend, specifically Sunday morning.
Note: The National Weather Service in State College has declared that the growing season has ended over the northern PA mountains as well as the Laurel Highlands, given the first bout of cold air early this week.
A series of cold fronts will cross Friday and Saturday, reinforcing cooler air each day. Lows Saturday morning will drop into the 40s, but as skies clear Sunday morning, temperatures will drop into the mid to upper 30s for much of northern and western PA.
Right now, it appears the coldest air should stay just north of the our viewing area, which means the first frost for south-central and southeast PA is still not in sight.
The average first frost for our area occurs between October 11-20, with the immediate Harrisburg area usually not experiencing it until October 21-31. The lowest temperature in Harrisburg so far this season is 44 degrees, which occurred Tuesday morning. With clouds and unsettled weather around next week, it is unlikely we see a frost through the end of the month. The latest sub-40 degree reading on record in Harrisburg was on November 4th, 1971, and the latest sub-37 degree reading (a typical frost threshold) was November 12th, 1920.
For comparison, here’s the first date of 36 degrees or lower from last year. For much of the commonwealth, this occurred in October and even as early as mid-September, a far cry from this year!
The month has been significantly warmer and drier than average, but we do foresee a more sustained period of average to perhaps below average temperatures by mid-November.
-Meteorologist Adis Juklo