* WHAT...For the Extreme Cold Warning, dangerously cold wind chills as low as 17 below. For the Cold Weather Advisory, very cold wind chills as low as 7 below expected. * WHERE...Northern Nassau, Northwest Suffolk, Southern Nassau, and Southwest Suffolk Counties. * WHEN...For the Extreme Cold Warning, until 1 PM EST this afternoon. For the Cold Weather Advisory, from 1 PM this afternoon to 10 AM EST Monday. * IMPACTS...The cold wind chills could result in hypothermia if precautions are not taken.