The freeze warning for Maricopa County has been extended another day, until 9 a.m. Wednesday.
A freeze warning means sub-freezing temperatures are "imminent or highly likely."
This is the coldest stretch of weather in the Phoenix metro since 1988.
In southern Arizona border city Douglas, Sunday morning's low of 7 degrees broke a record for January, according to the National Weather Service. The previous record in Douglas was 6 degrees on Jan. 4, 1949.
In northern Arizona, it was record -7 degrees at Flagstaff's Pulliam Airport on Sunday morning. The previous coldest low at the airport on Jan. 13 was 6 degrees below zero in 1963.
Low temperatures were in the mid 20s to the low 30s on Monday. Tuesday morning will be even colder.
If you're planning to be outside at all, wear warm layers that protect the head, hands, and feet. Cover sensitive vegetation with sheets and towels and wrap exposed pipes.