The proclamation alerts the public that the combination of temperature and wind chill will make it feel like 20 degrees or less, putting people without shelter in severe danger. The alert is set to expire at noon Monday, Martin Luther King Day.
In the Philadelphia area, the NWS predicts, Friday's temperatures will peak in the 40s but drop down to 26 overnight. Saturday's forecast high is 37 with a low of 25. Sunday should be even colder, with a high of 30 and a nighttime low of 19.
Monday should be sunny, in the mid-30s, before Tuesday warms up to the mid-40s. No measurable precipitation is in the weekend forecast.
The health department recommends checking general cold-weather invormation from the Centers of Disease Control and Prevention.