Tuesday, 19 February 2013

Southern Ontario Lake Effect Snow

Some key points I wanted to make on the upcoming lake effect snow outbreak across southern ontario

1. Wind alignment starts of as WNW before transitioning to NW and NNW later tonight and into tomorrow morning. Up to 40cm of snow may fall in areas along the shores of GB and lake huron with 850's crashing below -15c and favourable wind alignment aloft. Boundary level moisture will be present from 600 to 800mb with little to no wind shear throughout the region. All these parameters coupled with ice free lake huron and GB will allow for significant LES to set up across southern ontario.

2. I think the GB squall will be strongest and most extensive from midnight tonight through 8am tomorrow morning. This squall should extend into york region and the GTA in the early morning hours wednesday and thursday with accumulations up to 10cm in some spots. This band will weaken but continue to stay active across the barrie, meaford and wasaga areas into mid day wednesday. It should intensify again in the evening hours with significant impacts from meaford to collingwood stretching east to wasaga. I expect a re-intensification wednesday night into thursday morning with further impacts possible across york region again.

3. I am expecting the lake huron band to be stronger with several waves of snow squall activity from tonight into tomorrow afternoon with weakening by 1pm. This zone will set up from owen sound south to london including goderich, kincardine, walkerton, hanover, huron east and lucan. We are already seeing a first band of snow setting up across this region. Northern parts of this zone will get into the second heavy band from midnight to 4am. It should shift into the goderich and kincardine areas by 7am and lasting into the early afternoon. I think the most impacts on london will be from now until 11pm with a WNW flow dominating but they should avoid the second band for the most part. I think weaker but consistent bands of snow will continue to set up through wednesday afternoon and evening from blue water to kincardine. Another intense band should set up through the city of london wednesday night into thursday morning which will be their best chance at heavy snowfall from this event as the flow switches to NW. I am expecting the heaviest accumulations to stay NW of the city but 13-23cm in the city itself.

Here is my snowfall map for this event. In the GB and lake huron squalls i can see some 35cm accumulations locally but most accumulations should stay below 30cm in the dark purple zones.
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