A major winter storm is set to impact parts of southern Ontario/Quebec this weekend. While the models are depicting some pretty impressive amounts, there is still much uncertainty with this system. The lack of snowfall in these regions will lead to mistrust or disbelief towards the forecasts for this system, which could aggravate the situation if significant snowfall occur. A mix of lake-enhancement and high northerly winds could increase the felt impacts, even in regions that receive little snow.
Forecasting for winter storms is actually quite difficult. It involves tracking the Low pressure and where it develops. Shown above is one model simulation of where the surface Low pressure may develop and move northeast. Unlike summer rainstorms and thunderstorms, pinpointing the deformation zone is key. The deformation zone is the "line" or "zone" that separates warm precipitation from frozen. This location is the region that usually receives the most intense snowfall accumulations. This brings us to the model depiction below.
Depicted above is the GFS model and how the model is trending today. The deformation zone is indicated by the mixed-precipitation (ie where the pinks show up). North of this zone will be snow (in blue) and south (in green) will be rainfall. The closer you get from this mixing zone in the snow zone, the heavier the snowfall gets. The model runs above seem to be "trending" northward in track. This would bring the bulk of the snowfall in Southern Ontario and New York State. This brings us to "how much snow will we get?".
Above depicts today's GFS model trends for accumulating snowfall in inches and in centimeters. The accumulating snowfall corresponds with the northern track of the heavy snowfall. While it is too early to tell exactly how much snow parts of Ontario/Quebec will receive, there is general consensus that the 401 corridor on Saturday-Sunday will receive significant snowfall and areas of Niagara into New York State will receive very significant snowfall (40cm +).
One thing is for sure, significant cold air intrusion will make its way to Southern Ontario and Quebec on the backside of this system from Sunday lasting for a few days. There is the potential for -30's Celsius surface temperatures and wind chills approaching -40 for parts of Southern Ontario.
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Here is the forecast discussion by the National Weather Service in Buffalo, NY:
.LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/... ...Major Winter Storm Becoming More Likely This Weekend... The agreement between operational model and ensemble guidance continues to be very high, suggesting a large scale storm system with significant winter weather impacts for western and north central New York this weekend. Low pressure over the southern Plains Saturday is expected to gather strength as it tracks northeast toward the mid-Atlantic region Sunday. This system will have ample moisture and excellent baroclinicity to work with as a strong area of arctic high pressure nudges into the North-Central US. The current forecast track of the low places our region well within the cold side of the system. This will keep the entire synoptic portion of the storm as all snow and places the local area in a good location for significant snowfall amounts and associated impacts. The event looks to get under way during the day Saturday as leading edge of snow reaches western New York, with the event likely peaking Saturday night into early Sunday. As the low moves its way into New England during the day Sunday and into Sunday night, it will pull away the deeper synoptic moisture with it, however on the back side the coldest air of this winter season will be drawn down into the region and likely bring lake enhanced/effect snows to the region. This could bring significant additional snowfall totals, especially to areas south and southeast of the lakes, including the Rochester metro area. The lake response could easily last through early next week. Although this system is still a few days out, careful attention needs to be made to later forecasts as there will likely significant winter weather impacts for the region including heavy snowfall, bitter wind chills and strong gusty winds creating blowing and drifting snow creating difficult if not impossible travel conditions in some areas.