Friday, January 10, 2014

Heavy rain - flooding forecast

There is a house somewhere! An incredible amount of snow in Owen Sound, Ontario this week. Flooding is a big threat with heavy rain and rapid snow melt expected this weekend. (The Weather Network)
A major change in the weather will occur this weekend as arctic high pressure retreats back north and we are left with a very warm surge of mild and moist air form the Gulf of Mexico. But first one more cold morning with a low of -17C recorded here on L'Ile Perrot around 3am this morning, it has since warmed to -12C. The rest of the day will be cloudy with some light snow in advance of the main system and mild highs near -3C.

Warm air will continue to stream into southern Quebec overnight with perhaps a period of freezing drizzle or rain before dawn. By Saturday morning enough warm air will filter into the St. Lawrence Valley to change precipitation to all rain. Roads will be icy at the onset overnight but conditions should improve in the city by mid morning. It will remain rather icy across the Ottawa Valley and north of Montreal where freezing rain warnings are posted for tonight. The main concern once we switch to rain will be flooding. With surfaces frozen solid the water will have no place to go but runoff into lakes and rivers as well as pond on roadways. We have so much snow and ice around southern Quebec and Ontario that some flooding will be likely. Another issue may be river flooding where ice jams occur. For that reason a flood watch has been posted by the National Weather Service office in Burlington for all of Vermont and Northern New York. Flooding is also possible across Ontario and western New York where copious amounts of lake effect snow have occurred since Monday. Flooding from ice jams has already been reported along the Niagara River near Buffalo, NY.

It looks like general 25mm (1 inch) of rain is possible for all regions before it tapers to flurries by early Sunday morning as a cold front crosses the region. Temperatures on Saturday will be very mild from plus 5C to 8C (40-46F) forecast for southern Quebec and Ontario. They will drop to near 0C for Sunday.

No comments: