From the State Climatologist
The winter of 1997-1998 was one of the warmest on record. Winter is often defined by climatologists as the months of December, January, and February ("meteorological winter"). Minnesota experienced unusually mild temperatures in each of these months. The state-wide average temperature for December, 1997 was 23.6 degrees F, which is 10. 8 degrees above normal. January's average
temperature was a mild 14. 0, above the norm by 7.1 degrees. The month of February was extraordinarily warm, averaging 28.0 degrees, exceeding the normal by 14.9 degrees. The temperature for the 1997-1998 meteorological winter (December - February) averaged 21.9 statewide, which places this Winter second only to 1877-1878. The Winter of 1877-1878 is far and away the warmest Minnesota winter of the post-settlement era.
The warmest December - February temperatures in Minnesota's state-wide record are:
An asterisk (*) indicates an El Niño winter. Note that six of the seven warmest winters in Minnesota's recorded history occurred during El Niño episodes.