Snow was falling early Wednesday in the Tucson area and other communities across southeastern Arizona.
The state Department of Transportation reported whiteout conditions on State Route 90 near Sierra Vista and said it was sending plows to Interstate 10 in the Benson area.
The National Weather Service said snowfall by midmorning was beginning to decrease in Nogales in Santa Cruz County but was expected to intensity in Douglas in Cochise County as the morning went on.
Snowfall also was forecast in the White Mountains of east-central Arizona.
Forecasters issued a winter storm warning for the region until 5 p.m. MST.