Heavy rain and record warmth forecast for Montreal Monday

Heavy rain and record warmth should wash away any memory of last weeks snowstorm in Montreal. Despite nearly 40cm of snow falling this month, many parts of southern Quebec are looking at a green Christmas.

Heavy rainfall warning in effect for southern Quebec, with flood watches posted across Vermont and northern New York State.

Despite what the calendar says, a windy, warm and wet storm is on the way to southern Quebec. Strengthening low pressure off the South Carolina coast is forecast to move northward to lie near Lake Champlain on Monday. Deep tropical moisture is producing torrential rain and strong thunderstorms along many parts of the east coast today. Steady rain will overspread southern Quebec Sunday night, becoming heavy at times Monday morning, and ending late in the day.

At this time, a track just to our east is expected, resulting in up to 50mm of rain for Montreal, with some locations north and east of the city possibly receiving more.  The heavy rain may result in some localized river and urban flooding. The rainfall record for Montreal on December 18 is 52.4mm set back in 1878. Unseasonably warm air will also be in place, with a current forecast low of 5C (41F). The high on Monday will be close to a record-breaking 10C (50F). The current record for the date is 5.7C (42F) set in 1996. We should easily break the record, likely very early in the day.

NWS radar image showing strong low pressure developing off the Florida coast in the Gulf of Mexico on Saturday. This storm is moving rapidly north to lie near Lake Champlain late Monday afternoon.

As the storm moves northeast of Montreal, cooler air will move into the region. Any leftover precipitation will change over to light snow and persist into Tuesday. Some locations across far western Quebec and eastern Ontario may pick up a centimetre or two of accumulation. The temperature will drop to 0C (32F) by Tuesday morning, remaining fairly steady during the day.

Winds will become rather gusty Sunday evening, between 30 and 50km/h in the St. Lawrence Valley. Winds will back to the northwest between 20 and 40km/h Monday night persisting into Tuesday.