A Winter Storm Advisory is in effect from 7 p.m.
through 1 p.m. on Christmas day.
After rain falls throughout the day it will change over to heavy snow, quickly covering roadways.
The National Weather Service predicts 4-6 inches for Pittsburgh and much of the surrounding area with 6 to 12 inches in areas north and northwest of the city.
Temperatures will fall from the high 40s into the low 20s overnight.
And the snowfall could be a record-breaker for Christmas Eve and Christmas Day.
The Christmas Eve record for snowfall is 3.5 inches back in 1912 and the Christmas Day record is also 3.5 inches. That happened in 1909 and 1935.
PennDOT, city and county road crews will be out in force to treat roads, but the heavy rain will make it impossible to pretreat any roads.
Any salt will be washed away until the snow starts to fall. And with high winds and dropping temperatures, there will be plenty of slick spots, especially on bridges and overpasses.
The county will have 24 salt trucks out on the roads with extra drivers on standby.
With travel restrictions in place due to COVID-19, crews may have an easier time on the roads but drivers should still slow down and leave plenty of room between cars and plows.
PennDOT is advising motorists to avoid any unnecessary travel during the storm.