Potentially Historic ‘Nightmare Before Christmas’ Storm Threatens to Ruin Holiday Plans Across Southern Ontario
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NOTE: You can click on the map to open a zoomable image which will be easier to read.
We are watching what could be a life-threatening winter storm for Southern Ontario in the days before Christmas. You might be rolling your eyes reading this and thinking 'Oh yeah, another storm where we'll barely get anything'. And your skepticism is warranted as it has been quite a long time since we've experienced a storm of this scale.
However, it's important to emphasize that the particular dynamics of this upcoming storm are very concerning with the combined threat of a flash freeze, rapid drop in temperatures, destructive wind gusts and blizzard conditions. While there is still time for models to change, the confidence in this storm is quite high and you should be getting prepared now. We don't take a forecast like this lightly as it can cause a lot of stress, but it's a lot better to be prepared for the worst rather than being caught off guard.
The uniqueness of this storm has made us rethink our usual approach to forecasting a winter storm as the danger from this event isn't focused on one particular threat type (like heavy snow, wind or freezing rain). The concern is how the different threats will combine and help to maximize their impact on our region over the next few days. So we've decided to start our preliminary forecast with a regional look at the impact of this winter storm including the expected conditions on each day. We know many are trying to plan their holiday travel and that the timing of this event is what matters the most.
We have put together maps and forecast discussions for each region throughout Southern Ontario. We will still have our regular forecast maps including snowfall totals and maximum wind gusts, but the purpose of this is to provide a more holistic view of the impacts over the several days. Our full forecast will be released sometime late Wednesday or early Thursday.
IMPORTANT: There has been some confusion regarding the regional map. To clarify, the graphic on the right of each regional forecast is unrelated to the map. We have chosen to break down the impact and threat type by each day and went into detail about timing. The map shows the overall impact of this storm. We understand that using the same colour on the graphic and the map resulted in this confusion and we will be fixing it for future forecasts.
NOTE: You can click on the map to open a zoomable image which will be easier to read.
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For Southwestern Ontario, Thursday will start as the calm before the storm with temperatures near the freezing mark as you wake up in the morning. By the afternoon, temperatures will slowly rise into the low single digits along with some light rain moving into the region later in the afternoon. This rain will set the stage for our first hazard associated with this multi-day event when combined with an expected rapid temperature drop just after midnight and into Friday morning.
Temperatures will drop by 10-15 degrees in the span of a few hours resulting in a flash freeze throughout the region. Roads will likely become quite icy during the predawn hours on Friday. In addition to this, the rain will transition over to snow with more intense bands east of Lake Huron due to some lake enhancement of the system snowfall.
As the heavy snow continues with a particular focus on areas east of Lake Huron, the system will stall out over our region and rapidly intensify. This intensification will result in the development of some strong to damaging wind gusts ranging from 90-110km/h inland and even stronger directly along the shoreline.
Friday afternoon and evening are when we expect the worst conditions with gusty winds combined with heavy snow leading to blizzard conditions. Highway closures are almost certain and any non-essential travel should be avoided late Friday. The strong wind gusts will likely result in widespread power outages and make for a very dangerous situation with one of the coldest nights of the season so far on Friday. It will feel like into the -20s once you factor in the brisk wind chill. It's VERY important that you don't venture out in these conditions as when (not if) you get stranded in your vehicle, it will probably be a long time until emergency officials can get to you.
Snow squall activity will continue east of Lake Huron throughout Saturday and into early Sunday. This will likely lead to snowfall accumulation of over 50cm between Friday and Sunday for the Grey-Bruce region. The rest of Southwestern Ontario can expect around 15-30cm of snow by the end of the weekend. We hope that the power outages can be limited because Saturday and Sunday night appears to be just as cold making for one of the coldest Christmas in recent memory.
NOTE: You can click on the map to open a zoomable image which will be easier to read.
Temperatures will start on a mild note throughout the GTA on Thursday as warm air flows in advance of the approaching system. Daytime highs are expected to approach the mid-single digits as the rain starts to move in by late Thursday afternoon. The mild air will hold on throughout the evening and overnight with heavy rainfall. Total rainfall accumulation of up to 10-20mm is possible by Friday morning. Temperatures are expected to take a plunge by the late morning and early afternoon dropping over 5-10 degrees in a few hours. With the ground still wet from the previous rainfall, there is a strong flash freeze risk as roads will become quite icy.
Rain will turn over to snow by Friday afternoon across the Golden Horseshoe as we see the increase in wind gusts later in the day. Damaging wind gusts approaching 90-110km/h (higher in the Niagara region off Lake Erie) are expected during the evening and overnight hours. Power outages are possible in the hardest hit regions along with poor driving conditions due to blowing snow and even localized blizzard conditions in the Niagara region.
Snow squalls will also develop off Lake Erie and further enhance the system snowfall for the Niagara region. The heaviest snowfall rates will be found right along the Lake Erie shoreline including Port Colborne and Fort Erie. Lake effect snow activity will continue throughout the day on Saturday and into Sunday while the system-related snowfall will taper off for the rest of the GTA by early Saturday.
Current data suggests that much of the GTA could end up in a dry pocket when it comes to snowfall accumulation. At this point, most of the GTA will see around 5-15cm of snow over the weekend. The only exception is the Niagara region which will see snow squalls pushing totals into the 20-40cm range over the weekend. Localized spots right along the Lake Erie shoreline may even pick up more than that!
The main danger from this storm in the Golden Horseshoe will be the flash freeze risk on Friday late morning along with damaging wind gusts. Those who lose power from the wind damage could stay in the dark for an extended period due to the widespread impact expected. This isn't a good situation with the wind chill making it feel into the -20s over the weekend so be sure to have a plan in place to stay warm! And of course, the Niagara region will be heavily impacted by the snow squalls burying them in lots of snow along with blizzard conditions. Travel should be avoided in this region until conditions improve.
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NOTE: You can click on the map to open a zoomable image which will be easier to read.
NOTE: You can click on the map to open a zoomable image which will be easier to read.
The forecast for Central and Eastern Ontario is quite complex as it will start on Thursday with temperatures slightly below the freezing mark. Temperatures will only rise to near the freezing mark during the afternoon as light snowfall approaches the region later in the day. Those along the Lake Ontario shoreline are expected to be slightly warmer which will allow them to see light rain instead of snow. Snow (rain near the Lake Ontario shoreline) will continue to intensify throughout the evening and overnight on Thursday.
By Friday morning, there could be a brief warm-up throughout Central and Eastern Ontario allowing for the snow to switch over to rain for a few hours. Temperatures are expected to plunge well below the freezing mark later in the day as colder air floods into the region. As a result, there is the risk of a flash freeze especially around the Lake Ontario shoreline with a lot more rain on surfaces to freeze up. Expect icy road conditions during the afternoon as the temperature quickly drops which will also transition the precipitation back over to snow.
The worst conditions are expected late Friday into Saturday as the low-pressure system rapidly intensifies as it stalls out over the region. Lake-enhanced snowfall east of Georgian Bay and northeast of Lake Ontario will be the main focus with intense snowfall rates and blizzard conditions as wind gusts strengthen early Saturday. Regions including Muskoka, Parry Sound, Kingston and Prince Edward County will bear the brunt of this system with a focused snow squall developing off both Georgian Bay and Lake Ontario. Expect dangerous travel conditions throughout the hardest hit region during the morning and afternoon on Saturday. Avoid all non-essential if you can.
Wind gusts will also be an issue in this part of Southern Ontario but to a lesser extent. The only area expected to see near damaging wind gusts is along the Lake Ontario shoreline with gusts approaching 90-100km/h. Otherwise, wind gusts will range from 60-80km/h for the rest of Central and Eastern Ontario.
Snow squalls and very dangerous conditions will continue east of Georgian Bay throughout Saturday and into Christmas Day on Sunday. If you are in the affected regions, you should make plans to not travel on Christmas Day as roads in this area will likely be impassible due to the extensive amount of snowfall over the last few days.
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