The summer of 1983 was a hot one that extended into September. The middle of July produced the most extended bout of heat during this memorable warm season.
The ten days from July 11-20 had a mean temperature 11.7 degrees above the long-term average at the National Weather Service (NWS) near Negaunee. July 14th began the hottest period with a high of 95 and stifling low of 70 degrees. The Houghton area also hit 95 and Munising reached 100 degrees. In fact, this east-central lakeshore community had little or no relief from Lake Superior from July 11-16 as the temperature exceeded 90 on five out of six of those days.
The extended heat wave developed as a result of a classic mid-summer pattern over the central United States. A big upper-level ridge formed at about the longitude of the Great Lakes just to our south (Image above). Surface low pressure over southwest Canada and a high over the northeastern U.S. brought the U.P. a persistent southwesterly flow that pumped up oppressive heat and humidity.
The pattern to begin this week is the complete opposite of the one 31 years ago. Instead of a ridge, a big trough and associated upper-low is moving through the western Great Lakes (Image 2). This low contains a pool of cold, moist air. So until it leaves the area, we will have a threat of showers. At this point, it appears that the low will be far enough east by Wednesday for dry, slowly warming weather.