Overall May 2013 is running on the cold side of average. Through today, there have been only seven days with temperatures above average at the National Weather Service (NWS) near Negaunee. However, the three days starting Sunday were above average, with Sunday being the warmest with a high of 76 degrees. Areas in the south-central U.P. had highs in the lower 80s to start the work week. So it has been warm, but certainly not hot.
On the other hand, back in 1972, a warm spell reminiscent of summer affected the Upper Peninsula at this time. It actually started on May 18 when the temperature soared to 87 degrees at the NWS. The next day it reached a summery 90. From May 22-29, the temperature reached or exceeded 70 degrees reaching a high mark of 86 on May 28. At Ironwood where data goes back to the turn of the 20th century, consecutive record highs of 88 degrees occurred from May 17-19. The temperature also hit the upper 80s on the 24th and 25th. The warm, dry weather was brought by a highly amplified ridge that set up over the central U.S. after mid-month (Image 1 above). The system did not move or change much for days which kept a streak of warm, unchanging weather for an unusually long period over Upper Michigan.
What was noteworthy about the heat wave in ??72 is the weather conditions preceding it. The spring of 1972 was one of the coldest, snowiest and backward springs in the modern record. Snow cover remained in the city of Marquette until May __. Undoubtedly, it stuck around considerably longer in the hills west of town. The pattern suddenly shifted to summer after mid-month in May of 1972.
The summer, for the most part, did not continue the trend. May 1972 was over two degrees above average. Then June flipped and came in 3.1 degrees below normal. July and August 1972 were also cooler than average.
What does the summer ahead look like? There are indications that while moisture is now high after the big late winter and spring, things will again dry out and warm up. That is, if you buy the soil moisture model forecast put out by the Climate Prediction Center, a division of the National Weather Service. Its forecast has us warmer than average during June, July and August with below average rainfall (Image 2). Of course, this would be good in general for outdoor activities but not good for people who have low inland lake levels. Remember, this is only one model and frankly, models do not show much skill in seasonal forecasting.