Winter Sub-Freezing Periods and Significant Thaws in the Boreal Forest Region of Central North America
Keywords:Atmospheric temperature, Climate change, Cold adaptation, Ice cover, Lake ice, Melting, Snow, Snow cover, Storms, Synoptic climatology, Taiga ecology, Thermal regimes, Treeline, Great Lakes region, Canada/United States, Ontario
Winter daily maximum temperatures were examined for 56 sites in northern portions on Ontario, Michigan, Wisconsin, and Minnesota over the period 1960-88. The longest sub-freezing period of winter averaged 20-30 days in the southern portion of the region, 30-40 days around Lake Superior, and 90-100 days in extreme northwestern Ontario. These are twice as long as sub-freezing periods at similar latitudes in eastern Canada. The sub-freezing period is shortened by about one week along the shores of the Great Lakes. There is annual spatial correlation of the longest sub-freezing period, indicating regional synoptic-scale control. The late 1970s had the longest sub-freezing periods but no significant linear trend was found in lengths of sub-freezing periods. The average date of the first significant thaw (>10 C) ranged from early March in the south to late April in the north and delayed 1- 2 weeks along the shores of the Great Lakes.
Key words: winter, freezing temperature, boreal forest, Canada, Great Lakes