One of the most outstanding early April warm spells was in full swing in 1991. The National Weather Service (NWS) site near Negaunee hit the mid to upper 70s each day from April 5-7. An upper-level ridge built up ahead of a trough along the West Coast and drew warm air northward into the Great Lakes.
It was even warmer to the south and west. Ironwood reached a record-high 80 on April 6 and Iron Mountain set records of 84 and 85 on the 6th and 7th.
The warm spell came to a rude end on April 8-9. The trough progressed eastward and brought colder air and precipitation (Image 2). Over an inch of rain fell at the NWS on April 8. The rain changed to snow that night and over 7 inches of snow was on the ground the next morning.
April 1991 ended 4.8 degrees above the long-term average. It was part of an extended mild spell that saw record warmth in early February 1991, with well above normal temperatures from late winter through spring.