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      9-20-12-That's What Karl Says

      An unusually cold upper-air trough was responsible for measureable snow over portions of the U.P. on September 30, 1956.

      Measureable snow is a relative rarity in the Upper Peninsula during September. If it occurs, it will most likely hold off until after mid-month. The last significant September snow hit the west end in late September 1995. On the 22nd, plowable snow fell in Ironwood, with 2 inches in Ontonagon and 3 inches at the Houghton County airport near Calumet. Snow at lake-level (near Lakes Superior or Michigan) is really rare since the water retains some of the summer heat and makes it very difficult for snow to reach the ground. One notable exception occurred on September 21-22, 1974 when Marquette had nearly 5 inches of wet, heavy snow.

      Another notable snowfall happened 56 years ago today. On September 20, 1956, Sault Ste. Marie collected 2.7 inches of the white stuff. A disturbance rotating around an unseasonably deep upper-air low just to the east provided the energy for the snowfall (Image 1 above). The anomalously cold air mass associated with the low overcame the warmth of Lake Superior, despite the fact that the wind was cutting in off the lake. It was the Sault's largest recorded September snowfall.

      Back west in Marquette, there was measurable snow the day before. A cold rain changed to snow and brought just under a quarter inch. Much of the U.P. had at least a dusting of snow from this unusually cold system. This event wasnâ??t just a chilly bump in the road, either. Much of the month was cool. September 1956 ended with an average temperature nearly 5 degrees below normal.

      September 2012 is now running below average. Two days ago, a few spots in the highlands of the western U.P. had sleet and graupelâ??soft pellets of snow covered with a coating of ice. There is a possibility of more graupel or sleet in some of the highlands especially early this weekend as the core of the coldest air settles over Upper Michigan. However, most of the precipitation should fall as rain.