After another top-10 hottest summer in central PA, our weather flipped like a switch right as fall began. Our average temperature from September 22-29th was the coolest in that stretch since 2013. And, there are signs this seasonably cool pattern will continue through at least early October.


Last Saturday, temperatures dipped into the 40s officially for the first time since early May. Including today, we’ve now had nine straight days of lows in the 40s or 50s and highs in the 60s or 70s. This weekend will remain cool thanks to the remnants of Ian moving north and locking in clouds and rain. For some, it might be a struggle getting above the 60-degree mark.

Even as Ian departs us early next week, there’s a signal for more chill as we head toward the end of the week. An unusually strong trough, or dip in the jet, will move into the northeast, pushing quite chilly air into the region and likely our first chance of a widespread frost.

A cold front will cross the region sometime next Thursday or Friday, dropping temperatures into the 40s next Friday morning and eventually 30s for most of us next Saturday and Sunday. Frost requires calm conditions with mainly clear skies, both of which should be met next weekend as high pressure out of Canada gradually builds overhead.

The highest chance for frost or possibly even a light freeze looks to be over northern and western PA as temperatures dip into the mid and even low 30s. Locally, it will be a closer call with mid to upper 30s possible for most areas. Highs will only reach the upper 50s and low 60s. Keep in mind the normal high for us next weekend is still around 70 degrees with the normal low closer to 50.

First Freeze of the Autumn
The average first frost for south central Pennsylvania isn’t until late October and even early November for some areas south of the turnpike. Next weekend’s chill would come a few weeks ahead of schedule.
Expected departure from normal temperatures through early October.

Right now, it looks like the cooler pattern will last through at least the first 10 days of October, with milder conditions staying locked in across the far western US.

-Meteorologist Adis Juklo