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Wednesday snow storm potential in southern Ontario

By Chris Scott
Chief Meteorologist
Tuesday, March 11, 2014, 9:51 AM

After a few days of temperatures above freezing, you might be thinking that maybe, just maybe, we’re done with winter.


Those drab, brown patches of grass on which our vernal optimism tenuously hangs will be covered again on Wednesday as another storm system spreads snow across southern Ontario. Wednesday will be a cold, windy and snowy day for many.

The question is how much snow will fall.  

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As of Monday evening, our forecast team is thinking the worst of this storm will be along and south of the 401 corridor. Despite mild temperatures on Tuesday, temperatures will drop below freezing in the pre-dawn hours of Wednesday as the main pulse of precipitation moves in from the U.S. Midwest.

This ensures that all of the precipitation falling during the day on Wednesday will be in the form of snow. In fact, temperatures will fall from near freezing at dawn to -10 by Wednesday evening. With gusty northeast winds, Wednesday will feel like the dead of winter.

The forecast snow amounts have been very challenging to nail down for our team. While the big picture with this storm is set (low pressure tracking south of the Great Lakes Wednesday with the heaviest snow closest to the U.S. border), there is still considerable disagreement among the computer models we consult on the precise details of the track.

A difference of about 100 km in the track is resulting in millions of people in the U.S. and Canada being ‘on the fence’ in terms of getting a snow storm. The zone from Chicago through Detroit to Toronto and Montreal is the area on the edge of the heaviest snow.

Depending on which computer model you look at, amounts vary from less than 5 cm in these locations to well over… well, a lot. The least reliable computer model is giving a ridiculous total of nearly 70 cm of snow for Hamilton mountain. That’s NOT going to happen, but it shows you what our forecasters need to look at and why we have people and not just machines do our weather forecasting.

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Refinements are likely as we go into Tuesday, but as a general rule we’re looking at around 10-15 cm of snow along the 401 corridor, with higher amounts towards Hamilton, Niagara and the Lake Erie shoreline where 20+ cm is possible. Again, there is still considerable spread in the computer model guidance so expect some revision to these amounts on Tuesday. 

Regardless of the exact amounts, confidence is high for accumulating snow from Windsor through Toronto and Brockville, with difficult travel conditions at times especially through the west side of the GTA and into Niagara with strong northeast winds off Lake Ontario. Conditions will improve Wednesday evening as the storm system pulls towards the east coast, hammering eastern Quebec and New Brunswick.

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