Environment Canada says up to 20 centimetres of snow could fall in the Hamilton and Niagara regions by mid-morning on Christmas Day.
The weather agency is predicting that snow will be heavy at times on Christmas Eve and overnight with two to three centimetres per hour possible.
The snow should taper off to flurries by Friday afternoon. Freezing rain at times is also possible.
“Some uncertainty remains regarding total snowfall amounts, however, for much of the Niagara Region and areas just west, it appears 15 cm is likely enough to warrant a snowfall warning,” meteorologists said in a statement.
Motorists can expect deteriorating winter driving conditions from Christmas Eve into Christmas Day.
The general forecast for Thursday is calling for rain in the afternoon changing to snow in the evening with the temperature falling to -10 C.
A high of -2 C is expected on Christmas Day with periods of snow.