Mid-summer temperatures linger into fall for Great Lakes

Wednesday, September 21, 2016, 7:36 AM - Though fall is just around the corner, the Great Lakes aren't showing it.

The image below shows the lake temperatures as of Sept. 19, and they're running rather warm for this time of year. Both Lake Erie Ontario are sitting anywhere from 20 C to 25 C, Lake Huron and Georgian Bay anywhere from 17 C to 21 C.

FALL IS BACK: After a hot summer what can Canadians expect from fall? Find out with The Weather Network’s 2016 Fall Forecast | FORECAST & MAPS HERE

Lake Michigan has some large variations sitting near 13 C to 18 C along the western shores and up near 20 C to 23 C across the central and southern portions, which roughly averages out to between 20 C to 21 C.

Lake Superior is the most impressive of all the lakes, sitting near 15 C to 20 C. Now, comparing to the other lakes the numbers are not the warmest; however, when we factor in the depth and size of Lake Superior and compare the observed temperatures to what the average is for this time of year, the numbers are pretty impressive.

Before we investigate each lake individually, below are the lake temperature maps for this same time in 2015 and 2014. When comparing to this year, we can see the lakes have been retaining warmth from 2014 to 2016.

It appears the main factor as to why the lakes were able to get as warm as they are this year is the mild winter of 2015 to 2016.

From December 2015 through 2016, temperatures across the Great Lakes basin have been running above seasonal, with April the only exception. Factor in the drought this summer as well, which has led to ample amounts of sunshine, and it comes as no surprise the lakes are sitting near or even above their typical summer peaks as we head into the fall. Below we break down each lake individually.

Lake Superior

The graph above -- which will be the same type of graph for all the lakes -- shows the average lake temperature for 2016 (the red curve) compared to the 1992 to 2015 average (the blue curve). The solid black lines on the graph were added in by the author to make is easier for the reader to see how the current average compares to the 1992 to 2015 average and so the reader can better read where the current average sits on the temperature axis.

Right away we can see that for much of the winter Lake Superior has been running above average. In mid-August the lake peaked with an average temperature near 21 C, which is about 5 C above the normal summer peak, which sits near 16 C. The current lake average as we head into the fall is running well above the norm sitting near 17.5 C, with the normal for this time being about 13.5 C. Comparing the current average lake temperature to the summer peak it is still 1.5 C above the summer peak.

Lake Michigan

Lake Michigan is also rather impressive given its depth and size. Much like Lake Superior, Lake Michigan has been above average for just about the entire year thus far. Its average summer peak hit 24 C, which is 4 C above its normal summer peak. Its current average is still above the normal sitting at about 20.9 C, which is on par with the summer peak and is 2 C above the normal for this time of year.

Lake Huron

The trend continues for Lake Huron, which also ran above normal through most of the year thus far with a summer peak just shy of 23 C, which is 3 C warmer than what the normal summer peak is. The current lake average is sitting just a hair above 20 C, which is even with what the expected summer peak should be and is 3 C above the normal for this time of year.

Lake Ontario

The trend for Lake Ontario is much the same. For the most part of the year it has been running above normal with a summer peak near 24.9 C, which is just about 3 C above the normal summer peak. The current lake average is sitting level with the normal summer peak near 22 C and is about 3 C above the normal for this time of year.

Lake Erie

With Lake Erie being the shallowest of the Great Lakes, it's more susceptible to swings in temperatures. The winter of 2015 to 2016 being as mild as it was, the lake started out above normal and was up and down through February and March. The month of April saw a distinct cool-down in average air temperatures across the Great Lakes, which was about 1 to 3 degrees below normal. This influence is quite noticeable on the Lake Erie graph as opposed to the other lakes, since it’s so much shallower. However, once the summer months hit the lake ran away with its warming trend hitting a summer peak of about 26.2 C, which is slightly more than 2 C above the normal summer peak. The current lake average is actually in line with the normal summer peak of about 24 C and is about 3.5 C above what the normal lake temperature is for this time of year.

The most impressive stat seen here is that as we head into our first day of fall, the Great Lakes temperatures are at or just slightly above their normal summer peak temperatures. With the fall forecast across the Great Lakes expected to be above seasonal and with the early part of winter expected to trend as such, it is likely the Great Lakes temperatures will continue to trend above normal into the early winter. This could lead to an extended shipping season and may delay when the lakes will start to develop ice.

On average, most of the lakes start to develop some ice early to mid-December, and not until late December/early January for Lake Ontario. It’s near impossible to say for sure when ice will start to develop, but we can only speculate that it may hold off until late December for much of the lakes.

The milder lakes will also have a significant impact on the early lake-effect snow events. This does not mean they will be more frequent, but the milder lake temperatures will enhance the temperature contrast between the cold arctic air needed for squall and the lakes surface. This contrast will increase the instability over the lakes and allow for more moisture to be picked up in the squalls and then deposited over land as heavy snow.