Pre-Christmas storm forecasted in Ottawa with up to 20 cm of snow ...

Environment Canada has issued a snowfall warning for Ottawa and parts of eastern Ontario with a snowstorm expected to start on Monday afternoon.

The forecaster says snow will be heavy at times and will continue into the late evening. It all but guarantees a "white Christmas," which Environment Canda defines as having at least 2 centimetres of snow on the ground by 7 a.m. on Christmas Day.

While there remains some uncertainty with where the heaviest snow will fall, Environment Canada says most regions can expect to see near 15 cm with up to 20 cm locally.

"Rapidly accumulating snow could make travel difficult over some locations. Visibility may be suddenly reduced at times in heavy snow. Surfaces such as highways, roads, walkways and parking lots may become difficult to navigate due to accumulating snow," Environment Canda said in a statement.

Motorists are being asked to adjust their travel plans accordingly and to expect hazardous driving conditions.

The weather warning is also in effect for Gatineau, Smiths Falls, Perth, Cornwall and Brockville.

The snow is expected to taper off to flurries with a risk of freezing drizzle by Tuesday morning.

The forecast high for Ottawa is -8 C with a wind chill around -14. Overnight, expect the temperature to stay steady around -11 C with a wind chill around -14.

Tuesday's forecast is mainly cloudy with a chance of flurries and a risk of freezing drizzle in the morning. The afternoon high is -7 C.

Christmas Day is looking sunny with a high of -8 C.