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  • The Fall Storm Season

The Fall Storm Season

During November, it is not uncommon for powerful storms to track northeast across the Great Lakes region. Building arctic air masses across Alaska and Canada surge southeast into the Rockies and Plains States more frequently. At the same time, the still very warm waters of the Gulf of Mexico provide a source of heat and considerable moisture to fuel the development of low pressure systems riding the leading edge of the arctic air masses. These low pressure systems frequently organize in the lee of the central and southern U.S. Rocky Mountains. As the low pressure systems strengthen, they ride the jet stream northeast into the Great Lakes region. The relatively warm waters of the Great Lakes can cause these storms to intensify more than they might otherwise.

Even at the turn of the century 100 years ago, November was documented to be a month that produced strong storms over the Great Lakes region, posing a significant danger to shipping. In a paper published in a 1903 Weather Bureau Bulletin (in the early 1900s, Weather Bureau was the name of the current day National Weather Service) by Professor Edward B. Garriott entitled "Storms of the Great Lakes," 238 of the more important storms that tracked across the Great Lakes during the period 1876 to 1900 were described. With 45 severe storms in that 25-year period, November was the month with the most frequent strong storms in the Great Lakes region. That was followed by December and October. On average for that 25 year period, October, November, and December each had at least one but less than two severe storms. Thus, it has long been known that intense storm systems often move through the Great Lakes region in mid to late fall and in particular November.

The fall storm season coincides with the economic constraints of shippers wanting to get as many runs in before winter as possible, with the need for harvested grain to make it to market, and raw materials (ore, coal) to be stockpiled for winter. As storms become more frequent and more intense during autumn, ships more often encounter dangerous conditions as the strong winds associated with fall storms create larger waves.

audio link Being the largest of the Great Lakes, the waves on Lake Superior can build higher than on any of the other Great Lakes. The wave heights forecasted and recorded are the significant wave height, which is defined as the average height of the one-third highest waves--generally what an experienced observer would most frequently report. Significant wave heights of around 26 feet are about as high as waves can build on Lake Superior no matter how strong the wind is or how long it blows. This maximum significant wave height is constrained by the fetch or distance that the wind can blow across the waters of Lake Superior. Because of changing wind speeds, wind directions, wind duration and fetch, the actual state of the lake is comprised of a spectrum of wave heights. While the significant wave height is generally what is observed and recorded, it is very important to note that the rare peak waves can be as much as twice the significant wave height.

What follows is a brief description of two strong November storms. The November 9-10, 1975, storm caused the sinking of the Edmund Fitzgerald on Lake Superior. The November 9-11, 1998, storm is discussed since it occurred on the same days in November, followed nearly the same track, and was more intense than the ‘75 storm.

audio link Description of the waves in Marquette on November 10th, 1975
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