Weekend winter storm on tap for southern Ontario
This winter has certainly given us a variety of weather so far and it is looking the start to 2014 won’t be much different! More nasty, wintry weather will come in the form of a snow storm, then more bitter cold and snow squalls for southern Ontario. The forecast is looking rather complicated at this point in time so the following is a break down here to give you a better understanding at what we’re looking at and the possible scenarios.
In the image below, we are looking at Friday morning’s upper air analysis which will help set the stage for the incoming storm. What is shown below is the 500 millibar (mb) analysis across most of North America. Outlined are three areas of concern: The upper low on the eastern shore of Hudson Bay (1), the upper low near the Nunavut/Northwest Territories border (2), and the trough pushing into southern Alberta and extending back through British Columbia. These three features are important because ultimately how these three features interact will, in due course, determine how the weekend storm will pan out across the Great Lakes.
Taking a look at the surface in the image below, we can see the result of this pattern is the low that prompted warnings western Alberta, the southern Prairies, and into northwestern Ontario. The low pushing across the Prairies will stall over Hudson Bay having the two cold fronts merge and stall through southern and eastern Ontario Sunday. This cold front is expected to bring light snow across the region at that time.
As disturbance (3), shown in the very first image, dives south, it is expected to develop a Texas low along the stalled cold front and track into southern Ontario Sunday night through Monday. The timing and track of that low will depend on how the upper air pattern pans out.
The image below compares the NAM (North American Mesoscale Model) forecast model, GFS (Global Forecast System) forecast model, and Canadian (GLB) forecast model. The differences here are where they have the upper low centered and how far east the lobe of energy is through central and southern Ontario. The NAM has the upper low centered well to the south along the eastern shore of Lake Michigan and is skewed eastward with the pattern. The GFS/GLB have it centered near the northern shore of Lake Superior around the Marathon to Nipigon region and are skewed westward with the pattern. This is critical because it will have fairly major implications as to where the surface low will track and precipitation type.
At the surface we can see that this translates to the NAM being faster and skewing the surface low more to the west tracking it through Ontario. This would push the rain/snow line west introducing more rain for Niagara, into the GTA and eastern Ontario. The GFS and GLB track the low along the southern end of Lake Erie and Ontario and push the low up through eastern Ontario and into the St. Lawrence. This scenario has the rain/snow line further east from Niagara to Ottawa and a slight risk of some freezing rain. Please note that this is not another ice storm scenario by any means and any freezing rain expected would not be to the extent we saw before Christmas.
Another set of images below shows the comparison of all three models. The solid red line outlines the approximate position of where the rain/snow line will be according to the models solution for the late Sunday night and into Monday time period. Most areas will start as snow but to the east of the rain/snow line is where it is likely to have a transition to a mix of rain and snow or rain on Monday.
As this point in time, the forecast looks to favour the eastern track which is the colder solution of the GLB and GFS forecast models but looks like eastern Ontario will see slightly more rain on Monday than compared to southern and central Ontario. But this is likely to meander around some as the system gets better sampled as it progresses south and east where a greater observation network will allow more data for models to ingest and provide a little clearer picture.
In the set of images below illustrates the GLB and GFS forecast models snowfall forecast through to Monday afternoon. We stop the storm accumulations there for our purposes because in behind the low a fairly significant snow squall event will setup and we would like to focus on the storm hand first. The GFS and GLB snowfall forecasts show relatively good agreement but the GFS may have too much snow along the St. Lawrence Valley and into eastern Ontario as the warmer air and mixing precipitation will likely keep snow ratios a little lower. Based on current model data, a general range of 10 to 25 cm is reasonable for southern, eastern, and central Ontario and along the St. Lawrence River from Montreal to Québec. The ECMWF forecast model does support this scenario as well but that’s not to say the NAM isn’t correct here either. This is a setup that can vary dramatically as each model run comes in thus keep posted to get the latest information on how this system will develop.
Monday is a very busy day as kids are going back to school, some are returning to work so certainly budget a lot of extra time Monday morning for your commute. Though the snow should end by that time, roads may not be in the best condition. We could be dealing with school bus cancellations so ensure you stay up to date especially throughout the day and evening on Sunday as the storm moves in.
After the storm exits Ontario Monday, the brief warm up on the weekend will be a distant memory. Temperatures are set to plummet again late Monday into Tuesday with frigid Arctic air once again settling over the Great Lakes. This time, however, we will be contending with cold temperatures and strong winds. Sustained winds will be 30-40 km/h (higher over the lakes) so it will feel bitterly cold. These cold westerly winds will also kick up the lake effect snow machine with a classic westerly wind direction. Areas like Grey-Bruce, Huron-Perth, Barrie-Orillia-Midland and Parry Sound-Muskoka will be dealing with intense snow squalls Monday evening through Tuesday.