We have experienced an exceptional warm spell the last four days. Some locations had rising temperatures in the 60s last night. We have gone from a nearly three degree deficit in average mean temperature to near a degree above average for the month. This was a ??wet warm-up??, however. Abundant moisture kept us in the clouds much of the time and kept day-time highs in check. In the past, a drier atmosphere has given Upper Michigan much higher maximum temperatures in the run up to Halloween.
For instance, on October 25, 1874 it reached 71 degrees in Marquette. The late fall of 1874 was exceptionally mild. After a cooling trend brought a little snow on the 29th, more warmth developed in November, with high temperatures in the 60s from the 6th through the 8th. The mild spell culminated in a gale that tore away the front a residence in Marquette. The owner of the structure had "to move his family and household goods to other quarters."
One-hundred-fifteen years later, it got even warmer. On October 25, 1989, the temperature at the National Weather Service (NWS) near Negaunee soared to 75 degrees. The next day it hit 76, the warmest so late in the season. The week that began on October 23, 1989 came in at 19.6 degrees above the long-term average. This exceptional warmth occurred after a historic snowstorm hit the area on October 20-21. Then on October 22, it warmed to a high of 56. Over the next week, three days had highs in the 60s, with four days in the 70s. Finally by Halloween, things began to cool down. In contrast to 1874, there was no renewed warming in November. The eleventh month of 1989 began with cold and snow and never really let up. A permanent winter snow cover was established at the NWS by the opening of deer hunting season and the mean temperature for the month came in over five degrees below average.
Even after this remarkable warm spell, it appears we will wind up a little below average when October 2012 ends. The cold air that is surging into the western U.P. will likely hang around for awhile. That??s because of the highly amplified pattern that has developed (Image 1 above). A huge ridge has formed over the Eastern U.S. That means once the cold becomes established here, it will be slow to leave. In addition, Hurricane Sandy will likely travel up the East Coast and make landfall somewhere from the Delmarva to Boston early next week. The development of this potentially devastating system there will lock in cold high pressure here well into next week (Image 2).