The National Weather Service issued an extreme cold warning at 12:32 p.m. on Thursday valid from 7 p.m. until Friday 11 a.m. for Southern Herkimer. “Dress in layers including a hat, face mask, and gloves if you must go outside.”Understanding cold weather alertsExtreme cold warning: Take Action! An extreme cold warning is issued when dangerously cold air temperatures or wind chill values are expected or occurring. If you are in an area with an extreme cold warning, avoid going outside. A cold weather advisory is issued when seasonably cold air temperatures or wind chill values, but not extremely cold values, are expected or occurring.