At 12:51 a.m. on Thursday, the National Weather Service released an updated cold weather advisory valid between 1 a.m. and 10 a.m. for Northern Westchester and Southern Westchester as well as Putnam and Rockland counties. Understanding cold weather alertsCold weather advisory: Be Aware. A cold weather advisory is issued when seasonably cold air temperatures or wind chill values, but not extremely cold values, are expected or occurring. Extreme cold warning: Take Action! An extreme cold warning is issued when dangerously cold air temperatures or wind chill values are expected or occurring.