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Soaring Great Lakes temperatures could impact your forecast

Michael Carter

Monday, August 15, 2016, 10:00 - The persistent heat across the Great Lakes region this summer has sent water temperatures soaring, with all five lakes reporting temperatures well above the long-term average.

Water temperatures are expected to remain warmer than normal well into the fall and potentially beyond, which could have some significant impacts on your forecast – both positive and negative – for the rest of 2016.

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The table below shows the current difference between observed lake surface temperatures and the long term average as of Aug. 9. Temperatures from the same day in 2015, which was much closer to normal, are included for comparison. Values this year range from Lake Ontario at almost two degrees above normal to Lake Superior at a whopping 6.8oF (3.76 C) above normal.

What does this mean for your forecast as summer winds down and we move towards the cool season?

With the lakes running this warm, we expect to see an increased influence on temperatures in our coastal areas – especially on the overnight lows. The presence of warm water nearby can help to keep overnight temperatures from dropping drastically. This could delay the first freeze for some, which would extend the growing season – particularly for lakeshore areas like the Niagara Peninsula.

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Warm lake water can also have an impact on when we see our first early-season snowfalls. With the first few winter weather threats of the season, the difference of a degree or two in temperature often has a significant impact on who sees accumulating snow. Warmer lake temperatures can help tip the balance in favor of rain, especially in the lower lying coastal areas below the Niagara Escarpment.

On the flip side however, warm lake temperatures can increase the chance for significant early-season lake effect snows. As arctic air returns during the cool season, warmer lake waters increase the temperature contrast, and add more fuel for convective snow squalls. So if we do see a few shots of cold air in the late fall and early winter, warmer lake temperatures would increase the chance of seeing significant snow in the lake effect belts.

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Depending on exactly how long these above-normal temperatures persist, we could see impacts continuing well into the winter. Warmer water would delay the development of ice coverage across the lakes. This would extend the shipping season, allowing the lakes to remain navigable for longer, but also would extend the lake effect snow season.

However, it is worth noting that this warm water trend could be quickly erased by an extended period of colder than normal temperatures through the late fall and early winter. So as always, it’s important to keep an eye on the big picture when discussing the long term forecast.

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