Our heat wave continues and while there is some local cooling near the shores of the Great Lakes, most folks are still sweltering after a simmering night. The low this morning at the National Weather Service (NWS) near Negaunee fell to only 72 degrees. Ironwood, Menominee, Escanaba and Manistique shared the same low while Iron Mountain stayed at 73. It was only 75 in Houghton and 78 this morning in Munising. By late morning, the wind shifted northerly at Munising and the temperature actually fell back by a few degrees.
Low temperatures above 70 degrees do not happen very often at the NWS. Since record keeping started in 1961, there are only 10 instances where the low temperature on a calendar day stayed above 70 degrees. The earliest such occurrence was on June 18, 1995 when the low stayed at 72 degrees. That was during that record breaking heat wave that brought temperatures near 100 degrees in parts of the U.P. during the third week of the month. The latest over 70 low was August 30, 2010 when the temperature only fell to 72. The warmest low temperature on record at the NWS is a sweltering 74 set twice; first on June 28, 1971 and most recently on July 1, 2002.
Locations that stay dry tonight may stay at or above 70 for a low again. But relief is on the way. That promised change is slowly evolving. It still looks humid and quite warm Thursday. Then the main cold front will sweep across the area from late Thursday night through Friday morning. Showers and thunderstorms are likely during the transition. As is always the case in summer, rainfall will probably be spotty. With all the humidity, some heavy downpours are possible. Here is the output from our WSI RPM model through Thursday night (Image 2 above). It is soaking the western U.P. with 2 to nearly 4 inches of rain. It could happen; however, numerical weather prediction models are quite poor in forecasting summertime convective precipitation. One thing we are confident about is temperature. Cooler, drier air now building in Canada will sweep in during Friday and Friday night.