Unseasonably cold Canadian air heading into Iowa has caused the National Weather Service in Des Moines to issue a frost advisory for 1-8 a.m. Thursday.

This air mass is expected to drop temperatures to at or below freezing for an extended period of time. The weather service reports that significant areas of frost are possible across Central Iowa.

The weather service said that dry air may mean that the frost won’t be visible, but that damage can still occur to sensitive crops and outdoor plants. It recommends covering plants or bringing them indoors.