The Portersville area tied Donegal in Westmoreland County today for the coldest reported air temperature in the state with 20 below zero at 7:28 a.m.
That temperature does not factor in the wind chill.
Joe Palko, meteorologist for the National Weather Service, said the temperature dropped quickly overnight because there was no cloud cover and the snow on the ground.
That low temperature caused all public school districts in the county to cancel classes today along with Butler County Community College.
Slippery Rock University had classes but on a two-hour delay.