Frost in Pittsburgh on 4 Nov 2021 (photo by Kate St. John)

4 November 2025

Four years ago today I took a photo of frost because it was so late that year.

Though Pittsburgh’s killing frost date officially ranges from October 20 to 22, it was so warm in 2021 that we had no killing frost until early November when low temperatures were in the upper 20s for five days. The growing season ended abruptly.

This year, vegetation in my “urban heat island” neighborhood is still in good shape so we’ve had no killing frost here even though there was a freeze warning on 9 October (not!) and the temperature dipped to 31°F at the airport on 27 October.

I’ve marked this NWS graph of Pittsburgh temperatures last month with yellow on 9 October (we did not freeze at all) and a red box on 26 October (the one day that fell below freezing at the airport).

Because of the urban heat island effect, Pittsburgh’s growing season between frost dates could be mapped in micro climates with a warmer zone in the city and colder pockets in the creek valleys.

This graph was drawn with summer temperatures; I added October/November low temperatures to give you an idea of the variation in first frost.

Urban heat island profile across the landscape (graph from Wikimedia Commons)

So have you had a killing frost in your area?

Was it before or after the first frost at your National Weather Service forecast station?