Significant Winter Storm Could Impact Southern Ontario Between Thursday and Friday With Heavy Snow and Prolonged Freezing Rain

Confidence is growing in a potentially major winter storm that could have an impact on much of Southern Ontario later this week. There is still a lot to be determined including the exact precipitation type and hardest-hit locations/regions which will come down to the track and mixing line.

What we do know is that this will be an expansive system affecting almost all of Southern Ontario with some form of wintery precipitation. We expect it will begin sometime late Wednesday starting with rain with mild temperatures well above the freezing mark throughout the overnight and into Thursday morning.

This won't last long as colder air will flood into the region by early Thursday allowing for the rain to transition over to freezing rain, ice pellets and heavy snow. How fast this cooldown occurs will be key in determining the exact impact on our region. There could also be the risk of a significant flash freeze with the earlier rainfall and a rapid drop in temperature.

A second push of moisture will make its way into Southern Ontario by late Thursday continuing into Friday. Again, the exact precipitation type is unclear as it will depend on those temperatures. The two main concerns we have with this setup are the heavy snow and prolonged freezing rain potential. Starting with the heavy snow, we are looking at a swath of 15-30cm snow possible which currently appears to extend from Lake Huron and to the northeast through Muskoka and into the Pembroke/Renfrew region. Some other models show this further south bringing it into Southwestern Ontario, GTA and Eastern Ontario.

Further south, we are seeing what could be a prime environment for many hours of freezing rain starting late Thursday and lasting into Friday morning. Exactly where this line of freezing rain sets up will likely shift around as we get closer to the event. Currently, it looks like Deep Southwestern Ontario, the GTA and Eastern Ontario are at the highest risk for freezing rain. But this certainly isn't set in stone - it's important to be aware of the risk.

The dynamics with the freezing rain risk are fairly unusual where we normally see freezing rain before a major warm-up which limits the ice accretion. This won't be the case as a sharp cooldown will follow the freezing rain with temperatures remaining below the freezing mark for days to come. Prolonged impacts including power outages may continue into the weekend if this materializes.

We may have to start talking about an 'ice storm' with this event if the current data is correct but too early to say for sure. Again, lots can change so let's hope this doesn't happen as it could be very damaging.

We will continue to closely follow this and post a more detailed preliminary forecast hopefully sometime Tuesday. Stay tuned!