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      12-13-1976: Nearly Constant Bitter Cold

      The mean upper-air pattern in December 1976 delivered an almost constant supply of arctic air to Upper Michigan.

      Cold weather that began in the fall of 1976 continued into December, with a record low of 20 below zero at the National Weather Service (NWS) near Negaunee on the 13th. In Marquette the first 13 days of the month were below averageâ??most well below the long-term standard. On the west end, it hit 20 below in Ironwood on December 3. There was a relatively mild spell during mid-month, but then the cold returned over the last third of the month. On December 30, 1976, a bitter 35 below was registered at Ironwood. This was the coldest December reading on record until the historic cold snap in 1983 produced a low temperature of minus 36 on the 20th.

      A deep upper-air trough over eastern North America dominated the weather pattern during December 1976 (Image 1 above), while a ridge was a constant feature along the West Coast. This kept Upper Michigan under northwesterly flow and arctic air. This pattern was established in the fall and held on most of the winter. December came in nearly 7 degrees below average. January 1977 was over 8 degrees below normal. The cold finally eased during February as the month ended close to average.

      Our current weather pattern has featured a dominant westerly flow aloft. Cold air intrusions have been brief so far. On the other hand, arctic air has spread through a good share of Canada. Thompson, north of Lake Winnipeg in northern Manitoba reached 39 below last night and 44 below the previous night. Hudson Bay has quickly become nearly frozen over the past few weeks. For us, there are still no immediate signs that the arctic air will be released southward into the United States.