PENN TWP — Sub-zero temperatures returned to Butler County overnight, according to the National Weather Service.

The weather service’s reporting station at the Butler County Airport recorded the lowest temperature as 18 below zero at 5:30 a.m. today.

The forecast called for temperatures to rebound into the low-20s by this afternoon.

Here are the hour-by-hour readings at the airport:

Midnight — 6 below

1 a.m. — 8 below

2 a.m. — 8 below

3 a.m. — 8 below

4 a.m. — 13 below

5 a.m. — 11 below

6 a.m. — 17 below

7 a.m. — 11 below

8 a.m. — 15 below

9 a.m. — 0