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Raymond A. Assel

Abstract

General regional and temporal trends in maximum freezing degree-days (FDD's) are identified for the shore zone of the Great Lakes Basin for the 80 winter periods 1897–1977. The cumulative frequency distribution of FDD's at cub of 25 locations is used to define winter severity for the 80 winters. Graphs, contour maps and tabulations are used to summarize and portray the spatial and temporal distribution of FDD's and mild and severe winter categories of winter severity.

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Raymond A. Assel

Abstract

A positive 700-hPa Pacific-North America (PNA) circulation index in December 1989 was replaced by a negative PNA index in January and February 1990. This circulation pattern reversal was associated with an anomaly reversal in air temperatures over the eastern half of the United States and anomaly reversals in the air temperature, snowfall, and ice cover of the Great Lakes. Evidence of PNA teleconnections with these Great Lakes climatic variables for a 20-winter base period is presented through correlations of anomalies in the monthly 700-hPa PNA index and PNA coordinates with anomalies in Great Lakes average monthly air temperature, snowfall, and ice cover.

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Raymond A. Assel

Abstract

Annual seasonal average ice cover from 1973 to 2002 and associated dates of first ice, last ice, and ice duration are presented and discussed. The annual seasonal average ice cover of each Great Lake is used to define three ice cycle classes: mild, typical, and severe. About half of the severe ice cycles occurred from 1977 to 1982 and about half of the mild ice cycles occurred from 1998 to 2002. The seasonal progression of daily lake-averaged ice cover, spatial differences in ice cover, and differences among the Great Lakes for mild, typical, and severe ice cycles are discussed within the context of lake bathymetry and winter air temperatures. Seasonal average ice cover is larger on Lakes Superior, Erie, and Huron relative to Lakes Michigan and Ontario, because of shallower depths (for Erie and Huron) and lower air temperatures (for Superior) relative to Lakes Michigan and Ontario. This ice cycle classification scheme can be used to compare future Great Lakes ice cycle severity with this 30-winter benchmark.

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Frank H. Quinn, Raymond A. Assel, and Daniel W. Gaskill

Abstract

The objective of this study was to determine if the Niagara River ice boom has prolonged the Lake Erie ice cover at Buffalo, New York, resulting in significant changes in the spring warm-up of Lake Erie and longer, colder winters in the area. Statistical analysis of Buffalo air temperatures compared with those for Lockport, NY does not reveal statistically significant cooling in the climate at Buffalo related to the operation of the ice boom. However, because of the distance of the airport (where the temperature gage is located) from the shore zone, the possibility of a localized effect of small magnitude within the vicinity of the ice boom cannot be ruled out. A comparison of the water temperature at the Buffalo intake as recorded in pre- and post-boom years also indicates that the ice boom has not had an impact on the timing of the spring rise in Lake Erie water temperature at Buffalo. Analysis of winter temperature trends since 1898 shows that the winter severity at Buffalo follows a general pattern characteristic not only of the region around the eastern end of Lake Erie but also of the Great Lakes Region as a whole. Winters have become colder since the installation of the ice boom, but these colder winters are part of a general climatic trend toward more severe winters beginning in 1958. Thus, there is no evidence to suggest that the ice boom has increased winter severity or duration at Buffalo relative to other areas around the Great Lakes.

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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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Raymond A. Assel, C. Robert Snider, and Reginald Lawrence

Abstract

Winter 1983 was one of the mildest winters in the past 200 years. One result of the unusual winter weather was the mildest overall ice season on the Great Lakes since systematic observations of ice cover extent on the Lakes were initiated some 20-odd years ago. The 1983 winter developed during the peak of one of the most intense El Niño-Southern Oscillation events of this century. Associated with the mild temperatures in the United States was an extremely strong Aleution low that persisted most of the winter. Monthly Northern Hemispheric circulation patterns were generally weak; no general long wave patterns were able to persist; and 700 mb heights were above normal. Annual maximum ice coverage on the Great Lakes was much below normal: Lake Superior 21% (normal is 75%), Lake Michigan 17% (normal is 45%), Lake Huron 36% (normal is 68%), Lake Erie 25% (normal is 90%), and Lake Ontario less than 10% (normal is 24%). Economic impact of the below-normal ice cover included reduced U.S. Coast Guard ice breaking assistance to commercial vessels, reduced U.S. Coast Guard flood relief operations in connecting channels of the Great Lakes, and virtually no ice-related winter power losses at hydropower plants on the St. Marys, Niagara and St. Lawrence Rivers.

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