Southern Ontario: Winter Weather Hazards Outlook for Monday, December 27, 2021

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Forecast Discussion

A messy system is expected to move into Southern Ontario starting Monday morning. It appears that it will begin as some light to moderate snowfall to those north of Lake Erie. The Windsor and Chatham-Kent region should primarily see just rain although could be mixed at times during the morning. This snow won’t be too impactful with general totals ranging from 2-4cm (a few locations may pick up near 6cm and others might see only a trace). Due to the nature of this system, we can’t issue a precise snowfall accumulation map as it will be extremely variable depending on elevation and temperatures.

The main concern with this precipitation is during the afternoon and evening where we will see the snow begin to switch over to some freezing rain or drizzle. This risk is quite extensive including Sarnia, London, K/W and into the GTA. It won’t be particularly heavy, but it will linger for several hours. Expect some icy road conditions for your Monday evening commute. A thin layer of ice accretion on surfaces may result in isolated tree damage or power outages, but these should be very limited as the freezing rain will be very light.

The risk of freezing rain will shift into Central and Eastern Ontario later in the evening and overnight Monday. The Ottawa region should remain predominantly snow but they likely won’t see anything more than a few centimetres from this system.

Northern Ontario: Snowfall Outlook for Monday, December 27, 2021

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Forecast Discussion

A system is expected to track through Northern Ontario on Monday with a focus on areas around Lake Superior and the International border. Very limited to no snowfall accumulation is expected in Far Northern Ontario. The snow should begin during the morning hours on Monday along the International border and spread to the east by Monday afternoon. This will continue throughout the day with the potential for some blowing snow in some areas. The worst conditions will be found during the morning and afternoon. It will start to move out as we go into the evening but may linger around just past midnight for those near the Quebec border.

As for accumulation, there is a small area just to the southwest of Thunder Bay consistently showing up in the data with the potential to pick up as much as 30cm of snow. Other areas including Kenora, Fort Frances and Thunder Bay can expect around 10-15cm (maybe locally as much as 20cm especially near Thunder Bay). Northeastern Ontario around Lake Superior and into the Timmins area will see around 6-12cm on Monday with a few additional centimetres possible on Tuesday morning.

Southern Ontario: Winter Weather Hazards Outlook for Monday, December 27, 2021

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Forecast Discussion

There is the risk of freezing rain for parts of higher elevations to the northwest of the GTA over the Dundalk Highlands and into Central/Eastern Ontario. This will be primarily during the afternoon and into the evening on Monday. However, there is low confidence in the extent of the freezing rain at this point.

Battle of the Seasons Across Southern Ontario on Christmas With a ‘White’ Christmas Almost Certain for Central and Eastern Ontario

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This Christmas will be the story of two different seasons across Southern Ontario with a Green Christmas expected for much of Southwestern Ontario into the GTA, but further to the north, we will see the cold air hold on just long enough to maintain the existing snow on the ground and allow for a White Christmas. This won’t be a typical White Christmas as there will also be the threat of freezing rain during the morning hours on Christmas Day through Central and Eastern Ontario. Since temperatures will still be below the freezing mark, it shouldn’t melt any of the existing snowfall though it’ll be quite icy and slushy.

Temperatures rising above the freezing mark overnight into early Christmas morning combined with some rainfall are expected across the Windsor, Sarnia, London, Hamilton and Toronto corridor. This means that even if you have some snow on the ground tonight, it likely won’t be there when you wake up in the morning. Those over the higher elevations of the Dundalk Highlands and Grey-Bruce counties have a better chance as the temperatures will only get slightly above the freezing mark along with a more extensive snowpack from lake effect snow earlier in the week.

For more details on the freezing rain risk for Christmas Day, click on the image above to read our full forecast.

There is some uncertainty around the Simcoe County region and along the Georgian Bay shoreline which is dependent on how fast the temperature rises overnight. We believe the snowpack should be enough to hold on even with several hours above freezing. This is why we have a fairly expansive 75% zone as if we see a faster switch over to rain earlier in the overnight it could wash away most of the accumulation. However, this doesn’t seem likely at this point. To the northeast of Lake Simcoe, a White Christmas is practically guaranteed at this point, but again the freezing rain could make it quite sloppy and icy. As long as there is still 2cm of some type of snow on the ground in the morning then it’ll count as a White Christmas.

Freezing Rain Could Threaten Christmas Celebrations in Central and Eastern Ontario Between Friday and Saturday With Possible Power Outages

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It could be quite the icy start to Christmas across much of Central and Eastern Ontario as a system is set to move through Southern Ontario starting late Christmas Eve. For those in Southwestern Ontario and around the GTA, the precipitation will come down as rain which will wash away any hope of a White Christmas.

The problematic area will be around the higher elevations of the Dundalk Highlands and into Central/Eastern Ontario where some slightly colder temperatures will lock in at the surface with warmer temperatures above the surface. An hour or two of freezing rain is possible through Orangeville and Simcoe County late on Christmas Eve before it transitions over to regular rain after midnight. However, the main event will be over Central and Eastern Ontario where we expect a fairly expansive band of freezing rain to develop roughly to the northeast of Lake Simcoe and into the Ottawa Valley during the late evening.

The freezing rain risk will continue overnight and into Christmas Morning as current data suggests that the cold air will be quite stubborn so the freezing rain won’t switch as quickly as we see with most events. Some areas particularly around the Bancroft, Kingston and Brockville area could experience 6-12 hours of periodic freezing rain from Friday evening to Saturday afternoon. We will finally see the freezing rain taper off as we head into the afternoon hours, but some drizzle may linger into the evening. Note that areas around the Quebec border including the Ottawa Valley could see some ice pellets mix in which would reduce the freezing rain threat.

There is some concern with this event in particular as it won’t be followed by a warm-up or rain afterwards which helps melt any ice accretion. The only area this will occur is along the Georgian Bay shoreline and around Lake Simcoe. Instead, the freezing rain risk will only come to an end for more areas once the precipitation moves out during the afternoon. Temperatures will remain around the freezing mark and we expect even colder temperatures to flow in behind the system late Saturday into Sunday. This will mean that any ice accretion will remain on tree branches and power lines for several days and could cause power outages throughout the weekend as the branches and power lines buckle under the weight of the ice.

If you are travelling on Christmas Day in the affected area, you should be prepared for some potential icy road conditions. And be aware of the risk for power outages that may affect dinner plans on Christmas Day. However, don’t panic as the expected ice accretion is far from significant so hopefully any outages should be quickly restored. This won’t be anywhere close to an ice storm, but the timing makes it potentially impactful.