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      A Summer Heat Wave: May 21, 1994

      The trough that's been spinning out over the Northern Plains is finally drifting eastward into the Great Lakes.

      Back in 1994, Iron Mountain reached 92 for the second straight day on May 21. It hit 90 at the National Weather Service (NWS) near Negaunee, too. The pattern that brought the heat wave featured a sharp upper-level ridge that poked into the Upper Peninsula from the southwest on May 20, 1994 (Image 1 above). This heat wave followed one of the coldest winters in recent memory. While there was a blast of heat at the end of the third week of May 1994, the month as a whole was not particularly warm. The mean temperature ended right on average at the NWS.

      Our current pattern features an almost mirror image of what occurred 19 years ago. A trough is slowly struggling into the Great Lakes from the west (Image 2). This system has produced big rains in the northern Plains and deadly tornadoes in the southern Plains. It will weaken as it heads east. However, it will still produced rain here and will be followed by a chilly high-pressure system that will build in from the north (Image 3). This system will usher in chilly air on brisk northerly winds Thursday. Indications are that this fair-weather system will hang on through the Memorial Day weekend. The air mass associated with it will moderate slowly. But, it still looks like a cooler than average first holiday of the summer season.