Subzero cold greeted early risers across parts of the metro area on Monday, as the first in a series of polar air masses settled across the Great Lakes. Low pressure will pass across far northern Illinois Tuesday and Tuesday night, allowing temperatures to spike above freezing during the evening. The brief thaw means most of Chicagoland is due to receive a mixed bag of precipitation. Snow is expected to develop around midday Tuesday, becoming mixed with sleet, and rain or freezing rain as milder air spreads from south to north. All rain is to fall during the evening, before colder air sweeps back into the region during the overnight hours, changing rain to snow or flurries. Any precipitation after Tuesday night will be in crystalized form. Periods of light snow may accompany surges of arctic air Thursday afternoon, and again late Saturday.