Heat Wave of 2006 Derecho Series - Central Great Lakes-Upper Midwest Derecho (July 17, 2006)

Central Great Lakes-Upper Midwest Derecho (July 17, 2006)

While the northern part of the system was producing severe damage in Canada (northeastern Ontario and southern Quebec), an associated cold front led to significant damage in the US Midwest and Southern Ontario as it crossed the area later that same evening. There were dozens of reports of significant wind or tornado damage, especially in Michigan but also in southern Ontario, Wisconsin, Illinois, Iowa, and as far south as northern Missouri. The setup was similar along the long cold front, and the hot, humid air mass led to the damaging derecho, although the stronger derecho that affected areas well north of there formed much earlier that day in Upper Michigan just before noon local time. It had a clearly defined bow echo (squall line) formation, unlike these cells which were more fragmented. Relevant to the atmospheric dynamics at this time is the fact that that, according to the NWS forecast discussion from a number of stations, that a terrestrial subtropical storm had developed over Iowa and was moving slowly northeast—apparently this was a low pressure area devoid or almost devoid of extratropical characteristics.