Major Snowstorm and Prolonged Freezing Rain Risk To Hit Southern Ontario With Up to 15-30cm of Snow by Friday

After a fairly mild day across Southern Ontario on Wednesday, that will be coming to an end as an impactful system is set to dump up to 15-30cm of snow between Thursday and Friday. Earlier data indicated a more northern track which would have resulted in a fairly expansive freezing rain and even an ice storm threat. It appears the storm will indeed track further south with the colder air encompassing more parts of our region and making this a snowstorm for most locations. The Niagara region along with Prince Edward County and Kingston are the only exceptions to this which is still on track to see several hours of freezing rain.

The worst conditions are expected during the late afternoon on Thursday starting in Southwestern Ontario and continuing through the evening and early Friday morning. A very intense band of snow will work its way through the Sarnia, London, K/W, GTA, Peterborough and Ottawa corridor late Thursday which could bring hourly snowfall rates between 4-8cm for several hours. As a result, rapid snowfall accumulation is expected and will feel very reminiscent of the blizzard that dumped over 50cm of snow in the span of 6-8 hours exactly one month ago to the data as of Thursday.

The moisture associated with this system won’t be as intense as what we saw a month ago so snowfall rates exceeding 10cm are unlikely. Along with mixing and ice pellets being more prevalent with this system will help reduce potential accumulation. However, the immediate impact of this storm probably won’t be that different from what we saw last month because it’s impossible for road crews to keep up with the rapid accumulation. The long-term impact shouldn’t be as significant since 15-30cm of snow is the maximum that we’re going with which is around half of what the last storm delivered for many areas. It should allow for a faster and more efficient cleanup.

There is also the threat of a few hours of blizzard conditions with 30-60km/h wind gusts and very intense snowfall rates. Now, it might not meet the official criteria for a blizzard according to Environment Canada which requires blizzard conditions that last 4 hours or longer, but a few hours can still make travel near impossible during that time. Travel should be avoided starting late Thursday and if you can, stay home on Friday as many roads will likely still remain snow-covered. School bus cancellations and school closures are almost certain for Friday and some areas could even see them on Thursday due to the risk of freezing rain early in the day.

REGIONAL TIMING

TIP: You can click on either timeline graphic to open a zoomable version of the graphic.

We’ve already begun to feel the impacts of this system with heavy rainfall occurring Wednesday evening and will continue into Thursday morning. General rainfall totals will range from 10-25mm across Southern Ontario (Note: we have only included rainfall totals occurring after 6 am in the graphics above - although almost everyone will see heavy rain late Wednesday and overnight).

The first threat associated with this winter storm will play out just after sunrise on Thursday as cold air starts to flood into Southern Ontario from the northwest. This will push temperatures below the freezing rain starting with Central and Southwestern Ontario during the morning on Thursday. Due to the previous rainfall and melted snow, it’s quite likely that we see icy conditions developing on roads so be sure to drive very carefully on Thursday.

The cooldown thankfully appears to be more gradual over the span of 3-6 hours instead of a rapid drop so a traditional flash freeze is unlikely. This will continue to spread to the southeast throughout the day reaching the GTA by the early afternoon and Eastern Ontario by the mid to late afternoon.

As the cold air causes temperatures to drop, we will also see the rain slowly transition over to an hour or two of freezing rain and ice pellets before snow takes over. The exact switch over for each region is outlined in the regional graphics above, but it will occur sometime during the late morning and afternoon depending on your location.

The snow will likely start off quite light and there might even be a short break during the afternoon on Thursday before the second push of moisture moves into the region by the dinner hour. This second round will come in the form of snow as we expect most areas to have cooled down enough. A slower cool down could result in more ice pellets mixing in from Windsor, through the GTA and into the Ottawa Valley during the early evening. Depending on the extent of this slowdown, it could significantly reduce the potential snow totals in those regions so keep in mind the forecasted totals are conditional on that.

For the Niagara region and a small area around Kingston, it looks like the colder air could get stuck which would allow for the development of a fairly extensive band of freezing rain. Significant icing is possible for the aforementioned regions starting late in the afternoon and continuing past midnight. This of course will depend on the exact temperatures and if it’s slightly warmer it could come down as regular rain or slightly colder would mean more ice pellets or snow.

As mentioned, this wave of precipitation will bring very intense snowfall rates of 4-8cm per hour during the evening hours. That combined with the strong wind gusts will result in localized blizzard conditions and blowing snow. It will only last for 2-3 hours max, but during that time it will be almost impossible to travel anywhere so PLEASE stay home if you can late Thursday.

Conditions will improve overnight and early Friday morning as the snow becomes less intense and the system moves out of the region. We do expect a significant impact on the Friday morning commute as it’s unlikely that most roads will be cleared of snow by then so continue to stay home if you can.

SNOWFALL ACCUMULATION

By the time the snow tapers of early Friday, we are looking at widespread snowfall accumulation ranging from 15-30cm including Windsor, Sarnia, London, K/W, Toronto, Peterborough and Ottawa. A few localized totals could exceed the 30cm mark especially if temperatures end up slightly colder and allow for higher snow ratios. Mixing along the southern edge of this zone including Windsor and Hamilton could also decrease snowfall totals if the switchover is delayed.

For those along the Lake Erie shoreline and into the Niagara region, we are looking at between 5-15cm of snow along with the freezing rain threat with the snow coming predominantly early Friday morning after the switchover. Totals will also drop off further norther with between 10-20cm of snow extending from Goderich through Barrie, Southern Muskoka and Pembroke. The Bruce Peninsula and Parry Sound/Northern Muskoka are can expect around 5-15cm (likely closer to the lower end). Little to no impact is expected for Northeastern Ontario as this will be contained to Southern Ontario.

FREEZING RAIN ACCRETION

The focus of the freezing rain will be on the Niagara Region including St. Catharines and Niagara Falls late Thursday and Friday morning. Total accretion here could range from 6-12mm with locally as much as 15mm if it ends up lasting longer than expected. Kingston and Prince Edward County will likely end up somewhere around 4-8mm so we haven’t included them in the higher zone. The rest of the affected regions can expect a few millimetres of ice accretion during the switch over mid-day Thursday.

Keep in mind that this isn’t a typical freezing rain event which is usually followed by a warm-up and any ice to quickly melt. This event will be followed by another drop in temperature later on Friday and will stay below the freezing mark going into next week. Power outages are possible in the affected region and could even continue to linger into the weekend as the ice adds continued stress on power lines and trees. Be sure to charge up all your devices and be prepared for power outages.