On rare occasions, extra-tropical cyclones with central pressures below 28 inches of mercury or about 95 kPa (950 mb) have been recorded in Wiscasset, Maine (27.9") and Newfoundland (27.76"). The lowest central pressure for the 1978 blizzard was 955.5 mb (28.22 inHg) measured in Sarnia, Ontario. The lowest confirmed pressure for a non-tropical system in the continental United States had been set by a January 1913 Atlantic coast storm. The 956.0 mb (28.23 inHg) barometric pressure measurement recorded in Mount Clemens, Michigan, was the third-lowest non-tropical atmospheric pressure recorded in the mainland United States and the lowest in the Central United States. Toronto pressure fell to 28.40 inches, breaking its record by 0.17. At around the same time, the absolute low pressure was measured at Sarnia, in Southwestern Ontario, Canada, where barometer readings decreased to 955.5 mb (28.22 inHg). In Detroit, air pressure fell to 28.34 inches of mercury (960 mbar). There, barometer readings fell to 956.0 mb (28.23 inHg). ![]() On January 26, the third-lowest atmospheric pressure recorded in the mainland United States, apart from a tropical system, occurred as the storm passed over Mount Clemens, Michigan. In London, Ontario, 41 centimetres (16 in) of snow fell the maximum wind-speed was 128 kilometres per hour (80 mph). In Canada, the storm caused blizzard conditions across southwestern Ontario. Wind chill values reached −60 ☏ (−51 ☌) across much of Ohio, where 51 of the at least 90 storm-related deaths occurred. Winds gusting up to 111 miles per hour (179 km/h) caused drifts that nearly buried some homes. Muskegon, Michigan, had up to 33.8 inches of snow in four days due to heavy lake-effect snow squalls after the blizzard began. Particularly hard hit were Illinois, Indiana, Kentucky, Michigan, Ohio, and southeastern Wisconsin. As the storm headed for Ohio, it was "of unprecedented magnitude", according to the National Weather Service, which categorized it as a rare severe blizzard, the severest grade of winter storm. The storm initially began as rain, but quickly changed to heavy snow during the predawn hours (as Arctic air deepened ahead of the storm), leading to frequent whiteouts and zero visibility during the day on January 26. To be classified as undergoing explosive cyclogenesis, a storm's central pressure must drop at least 24 millibars, or an average of 1 millibar per hour, over a 24-hour period the Great Blizzard dropped by a remarkable 40 millibars in that 24 hours. These Arctic and subtropical jet streams merged (with maximum winds of 150 knots) which led the deepening Gulf low-pressure system, which had moved over Alabama and Georgia, to undergo explosive cyclogenesis and move rapidly northward towards West Virginia during the evening of January 25 (with record low pressures were logged across parts of the South and Mid-Atlantic). A powerful Arctic jet stream (containing a wind max of 110 knots) surged straight south through the Northern Great Plains while a powerful subtropical jet (containing a wind max of 130 knots) moved south through Arizona, both during the time a huge upper ridge of high pressure forced the Pacific jet north into Northern Canada. Late on Tuesday, January 24, 1978, surface maps revealed a moisture-laden Gulf low-pressure system developing over the southern United States, while a separate and unrelated low-pressure system was present over the Upper Midwest. The third lowest non-tropical atmospheric pressure ever recorded in the mainland United States occurred as the storm passed over Mount Clemens, Michigan, where barometer readings fell to 956.0 mb (28.23 inHg) on January 26. It is often cited as one of the most severe blizzards in US history. The Great Blizzard of 1978 was a historic winter storm that struck the Ohio Valley and Great Lakes regions of the United States as well as Southern Ontario in Canada from Wednesday, January 25 through Friday, January 27, 1978. Part of the 1977–78 North American winter ![]() Surface map on the morning of January 26, 1978Ĭentral United States, Eastern United States, Eastern Canada
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