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  • Author or Editor: Raymond A. Assel x
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Raymond A. Assel, John E. Janowiak, Sharolyn Young, and Daron Boyce

The Laurentian Great Lakes developed their most extensive ice cover in over a decade during winter 1994 [December–February 1993/94 (DJF 94)]. Extensive midlake ice formation started the second half of January, about 2 weeks earlier than normal. Seasonal maximal ice extent occurred in early February, again about 2 weeks earlier than normal. Winter 1994 maximum (normal) ice coverages on the Great Lakes are Lake Superior 96% (75%), Lake Michigan 78% (45%), Lake Huron 95% (68%), Lake Erie 97% (90%), and Lake Ontario 67% (24%). Relative to the prior 31 winters (1963–93), the extent of seasonal maximal ice cover for winter 1994 for the Great Lakes taken as a unit is exceeded by only one other winter (1979); however, other winters for individual Great Lakes had similar maximal ice covers.

Anomalously strong anticyclonic circulation over the central North Pacific (extending to the North Pole) and an abnormally strong polar vortex centered over northern Hudson Bay combined to produce a circulation pattern that brought frequent air masses of Arctic and polar origin to the eastern third of North America. New records were set for minimum temperatures on 19 January 1994 at many locations in the Great Lakes region. A winter severity index consisting of the average November–February air temperatures averaged over four sites on the perimeter of the Great Lakes (Duluth, Minnesota; Sault Ste. Marie, Michigan; Detroit, Michigan; and Buffalo, New York) indicates that winter 1994 was the 21st coldest since 1779. The unseasonably cold air temperatures produced much-above-normal ice cover over the Great Lakes and created problems for lake shipping. Numerous fatalities and injuries were attributed to the winter weather, which included several ice and snow storms. The much-below-normal air temperatures resulted in enhanced lake-effect snowfall along downwind lake shores, particularly during early to midwinter, prior to extensive ice formation in deeper lake areas. The low air temperatures were also responsible for record 1-day electrical usage and multimillion dollar costs associated with snow removal, U.S. and Canadian Coast Guard operational assistance to ships beset in ice, damage to ships by ice, damage to public and private property by river ice jams and associated flooding, frozen underground water pipes, and damage to fruit trees.

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Raymond A. Assel, Frank H. Quinn, and Cynthia E. Sellinger

An extreme low-water supply episode from 1997 to 2000 resulted in the largest 1-yr drop in Lakes Michigan–Huron and Lake Erie water levels (0.92 and 1.03 m, respectively) recorded since measurements began in the early 1800s. Lake Superior water levels were the lowest since 1925. Lakes Erie and Ontario also had relatively low levels. The episode was unusual, particularly when compared to the record-low water episode of the mid-1960s, in that the primary hydroclimatological driver was high air temperatures and not extremely low precipitation. The high air temperatures resulted in unusually high lake evaporation rates and decreased basin runoff. The drop in levels during this episode was compared to other 1–3-yr decreases throughout the period of record. A comparison of the 1997–2000 episode for Lakes Michigan–Huron with the 1960–64 episode, which led to record-low lake levels in 1964, shows that the various elements of the water balance have differing importance in the two episodes.

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