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Meteorologist Brett Soderholm on the Colorado Low tracking towards parts of Ontario this weekend.

Great Lakes to significantly impact southern Ontario, soon

Brett Soderholm

Thursday, November 17, 2016, 8:32 AM - Warmer-than-average Great Lakes temperatures this year are poised to have a significant impact on southern Ontario’s weather in November.

Recently observed data from the Great Lakes Environmental Research Agency has indicated that the average surface water temperature across all five of the Great Lakes is presently at least 3oC above normal for this time of year, and at least 4oC above normal for the lakes surrounding the most densely populated region of Canada.

No, this isn’t another one of those articles attempting to link observations like these to climate change (I’m a meteorologist after all, not a climatologist).

Rather, this is a simple (albeit preemptive) cautionary tale for residents of Southern Ontario as we head into the latter half of fall, or as I like to call it, “lake-effect snow season.”

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With the honeymoon-phase of fall that is the months of September and October now over, it may be tough to accept the fact that we are now slowly beginning the long (and increasingly chilly) journey through the part of season that is notorious for developing lake-effect snow squalls and lake-enhanced snowfall accumulation in Southern Ontario.

Lake-effect snow is particularly common throughout the months of November and December because it is normally the time of year when the temperature difference between the air over the Great Lakes and the air over land is greatest. Empirical evidence shows us that a difference in temperature between these two locations must be at or exceed 13oC in order for lake-effect snow to become a real concern.


Given this, if the lakes are a few degrees warmer than they usually are this time of year, it will be that much easier for the temperature difference to attain or exceed that important 13oC threshold when a cold airmass eventually moves in, which it invariably will.

Once that threshold is attained, if the prevailing winds blow consistently along the greatest fetch of the lake, you’ve got yourself a perfect set-up for particularly impactful lake-effect snow event for those downwind.

In fact, this month marks the two year anniversary of Buffalo’s now-infamous “Snovember:" a historical lake-effect snow event that dropped over six feet of snow in just over three days.

To read more about how that event happened, and the general science behind lake-effect snow, click here.

Of course, given the recent unseasonable temperatures in southern Ontario, you might find it hard to believe that lake-effect snow could possibly be something you need to worry about in the near future.

But with two passing cold fronts this week, temperatures will take a brief dip to below-seasonal.

The second cool-down, which will approach on Friday, will bring significantly cooler temperatures aloft -- which is one of the main factors that contribute to lake-effect snow potential.

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While lake-effect snow showers will likely take place this weekend -- which is to be expected for this time of year -- accumulations will not be significant, and it will not pose any sort of risk to travel.

November remains a major transition month for southern Ontario. Daytime high temperatures at the beginning of the month can still be in the mid-to-upper teens, although it's difficult for them to attain double-digits near the end of the month.

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Indeed, as we progress into the third and fourth weeks of the month, there are still strong indications of a country-wide temperature pattern reversal: Warming in the west, and significant cooling in the east.

When you combine this projected temperature drop with warmer-than-normal Great Lakes, you can almost confidently bet that a significant lake-effect snow event is in the cards for somewhere in southern Ontario.

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