From NWS Pittsburgh:

We want to stress again how impactful next week's arctic system will be. Forecast data suggests that when daily average temperature is 12F below normal during mid-January for 48 hours or longer, SIGNIFICANT impacts are expected (including, but not limited to frozen pipes, frozen sprinklers) with extra caution encouraged for emergency managers, fire departments, building managers, and the public. 

The current forecast calls for 2-3x COLDER or 25F to 35F below normal in the Monday to Wednesday period with the coldest day forecast Tuesday. 

In the WARMEST SCENARIO, high temperatures Monday/Tuesday are in the low 10s and lows Tuesday/Wednesday morning are near 0. In the colder (and more likely) scenario, daytime highs may be in the single digits to near 0 with lows approaching -10F.

Jeff, WB1AAL