Lake Superior ice and how it Effects Snowfall

LAKE SUPERIOR ICE COVER
The more Lake Superior is covered with ice, the less lake effect snow there will be. In the last 30 years, apparently due to global warming, the Lake has been on average less covered with ice which has, as expected, led to more lake effect snow.

Global warming has apparently led to less ice cover on Lake Superior and thus more snow in Big Snow Country. However, there is evidence that climate variation over any 100 year period, regardless of and apart from any overall global warming, has played an even bigger role in determining the actual snowfall in Big Snow Country. It seems that across many decades, how cold it gets on average in the winter has varied in patterns (or waves) lasting about three decades each, completely separate and apart from overall global warming.

So far, extra snow from global warming alone would hardly be noticed on top of all the snow that falls with or without global warning. Assuming that global warming is real, it is apparently true that global warming has already led to an increase of roughly 10% in the snowfall in Big Snow Country.

Historical evidence indicates that from about 1860 until about 1980, Lake Superior most often was completely iced over for at least several miles out, for the first few miles from the American southern shore, by the holiday season: the last week of December. Since 1980, it has more and more taken almost three weeks longer than that for the shore area to ice over, until about the middle of January.

From 1860 until about 1980, Lake Superior ice cover near and along the southern shore usually melted away as of the middle of April, by the 20th of April at the latest. Since 1980, the near shore ice cover has been on average melted away almost three weeks sooner, by about the end of March.

The Lake ices over from shallow water near the shore outward. In very severe winters, the Lake becomes almost entirely iced over, including even most of the middle of it. Such winters have become less common, although the 2008-09 winter defied recent history and was cold enough to be classified as a severe one. In a mild winter, which apparently is more likely now due to global warming, the Lake, even at peak ice, may be iced over only relatively near the shore, with greater ice cover further out into the Lake on the Canadian side than on the American.

Peak Lake Superior ice is reached during mid or late February. The greater the percentage of the Lake that is iced over, the slower it will melt. On the other hand, just like on land, melting increases from one week to the next during March and April. Late April "melting power" is probably 10 times early March "melting power.

In the century up until 1980, the Lake on average became almost half iced over by mid February, with the deepest waters well out from the shore (starting about 25 miles out) remaining ice free except in colder than normal winters. There was (and still is) quite a bit of variation in Lake Superior ice cover from year to year. During the 1880-1980 century, in the most severe winters, the Lake became up to about 90% iced over. In the most mild winters, the Lake became as little as 15% iced over (near the shores only.) Whether the ice has ever become literally 100% iced over is unknown.

There were patterns during the century for which there is some scientific information. In general, from about 1898 until about 1922, Lake Superior averaged substantially more peak ice coverage (in February) than the overall 45% average for the century. Then from 1922 until 1958, Lake Superior averaged substantially less peak ice coverage than the overall 45% average. From 1958 until 1982, Lake Superior peak ice coverage became substantially higher than 45% again. Since 1982, Lake Superior peak ice coverage has been substantially below 45% again.

From the foregoing and also from actual historical snowfall records, we know that:
1898-1922: Lake effect snow was less than the 100 year average, probably about 15-25% less judging from available recorded evidence.
1922-1958: Lake effect snow was heavy, probably about 15-25% more than the 100 year average.
1958-1982: Lake effect snow was less than the 100 year average, probably about 15-25% less.
1982-current: Lake effect snow was heavy, probably about 15-25% more than the 100 year average.

For example, consider Houghton. It has been averaging about 220 inches of snow a year over the last 30 years, within the low ice and heavy snow combination. If this snow is actually 20% higher than the 100 year average, then that 100 year average is about 183 inches, which is about what in fact it is. If the Lake were to again start largely icing over again at peak ice in February (which appears to be very unlikely despite the surprisingly cold 2008-09 winter) then Houghton's expected snowfall might be as little as 146 inches per year. Note that the swing caused by the high ice versus the low ice historical periods is such that the low ice periods produce about half again as much snow as do the high ice periods.

As we have just seen, since 1982, the percentage of the Lake surface that ices over at the peak has on average been substantially less than the century average of 45%. Open water is the original source of lake effect snow, not iced over water. The more miles of ice the clouds packing the lake effect snow have to travel over before reaching land, the more the snow will fall on the ice on the Lake, and the less the snow will fall on the land.

Big Snow Country is researching whether any scientist has yet discovered the relationship between lake snowfall and how many miles of ice there are between the open water and the land.

Find out how much ice cover there is on Lake Superior at this time here. Click on the map there to make it larger and readable.