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      September 23: The Cold Season Closes In

      An usually cold, deep upper-air trough produced significant snow in the city of Marquette on September 21-22, 1974

      On Friday it was pointed out that September 22nd brought some significant snow to scattered areas of the U.P. in the fairly recent past. Right about this time, the first signs of winter will sometimes show themselves to Upper Michigan residents.

      For instance, Ironwood??s earliest measurable snow was 2 inches on September 21, 1913. Then there was the big snow (6.5 inches) on September 22, 1995. An inch of snow fell on September 23, 1989, while 2 inches came down on September 24, 1942.

      A hard freeze was reported in Iron Mountain and at the National Weather Service (NWS) near Negaunee on September 23, 1974. Both stations fell to 22 degrees??the coldest so early in the season. Even the Houghton County Airport near Hancock, exposed to the moderating effect of Lake Superior, recorded 26 degrees. Some other cold events around this time include 20 degrees at Iron Mountain on the 25th in 1947. In 1965, a cold air mass dropped in from Canada and the NWS recorded a 21 on September 27, 1965. That cold spell brought Iron Mountain??s earliest snow on record (since 1949) the day before when 1.5 inches fell.

      When snow comes to Upper Michigan during September, it??s tough to get it to fall along the Lake Superior shore. The lake still retains a good share of its summer warmth. Look at Munising. Since 1949, the only measurable snow in September fell on the 29th 1951. The whopping total was one-tenth of an inch. On the other hand, a rare significant snow fell in the city of Marquette on September 21-22, 1974 during the aforementioned cold spell. An unusually deep, cold upper-air trough settled into the western Great Lakes and brought with it the right combination of wind direction, cold air and moisture for a total of 5.1 inches of snow (Image 1 above).

      Snows in September are rare. Consider this: the mean date of the first measurable snowfall ??on the hill?? at the NWS is October 13. Since 1979, the earliest date is September 22, 1989. The latest is November 21, 1994. The mean date in the city is October 20. The earliest date there is early. On September 19, 1956 two-tenths of an inch was measured.

      It appears we will have to wait until October for our first measurable snowfall this year. A big upper-level ridge has built over the Upper Great Lakes. This feature will bring us warm, dry weather through the week. There are signs of change to a cooler, unsettled pattern starting this upcoming weekend. But this looks like run-of-the-mill early fall chill into early next week.