Warm Great Lakes Influence on Climate

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Implications of very warm Great Lakes surface: Warm-biased autumn BUT potentially a big lake-effect snow-make early winter.

Discussion: About 80% of the Great Lakes are much warmer than normal as October 1st approaches. Far western Lake Superior and southwest Lake Michigan are cooler than normal due to westerly wind up-welling deeper cool waters otherwise the Great Lakes are very warm. The warmer water surface will have a tendency to moderate any cold air masses moving south from Canada or eastward from the North-central States. This effect delays first frost and freeze. Made difficult is any long-lasting chill south and east of the Great Lakes through autumn and into early winter. However, if unusually cold (arctic) air moves across the relative warm Great Lakes in November or December unusually excessive lake-effect snows will occur. Winter-time cold weather is dependent on the presence of snow cover. So the excessive warm Great Lakes (now) could eventually lead to a condition that produces widespread heavy snows which could sustain following cold.

Fig. 1-2: Daily SSTA across the Great Lakes reveal most of the lakes surface is a whopping 2.5C to 4.0C warmer than normal (left) and the 30-day trend has mostly been much warmer (right).