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A record-high of 73 degrees was recorded on April 10, 1977 at the National Weather Service (NWS) near Negaunee.  That temperature is not at all eye-popping after the historic heat of three weeks ago.  But it was a big deal 35 years ago because of the remarkable flip in the weather pattern.  Two days before, the NWS got down to 5 below zero. 

The first five days of April 1977 were cold and stormy.  Over a foot of snow fell during this time in Marquette, with much more in the higher elevations away from Lake Superior.  For instance, 12 inches of snow fell in Iron Mountain on April 4-5—the heaviest storm so late in the season.  The maps on April 5 showed a deep upper-level trough right over the western Great Lakes (Image 1 above) with a strong surface low to the east over the Lower Peninsula (Image 2).  This is a perfect set up for heavy snow over a good share of Upper Michigan.  After the snow, cold high pressure settled in for the record cold on the morning of April 8 (Image 3).  Then the dramatic flip in the pattern occurred.  The strong trough of the 5^th was replaced by an upper-air ridge on the 10^th (Image 4).  Low pressure developed over the Dakotas and sent warm air surging into the U.P. on strong southerly winds (Image 5). 

This warm surge, like our March heat wave, had staying power.  High temperatures hit 70 or above on three consecutive days in Marquette.  In Iron Mountain record highs in the low 80s were recorded on April 9-10, 1977, while Ironwood hit 83 degrees on April 10. 

Currently, the coldest air relative to average since the historic March warm spell is flowing in on northwesterly winds.  This will be a relatively brief surge as the persistent upper-air ridge that has dominated over the last several months flexes its muscle again over the Upper Great Lakes.  That will mean another warm up to above average later in the week.