During the lumbering era of the late 1800s, a number of forest firm blazed across the upper Midwest. The climatological conditions in the months before these disasters have already been presented in other studies. This paper reconstructs the synoptic weather patterns that consolidated and spread the 1881 fire (4–6 September) in Michigan's Thumb area (east-central Lower Peninsula) from historical surface data. These analyses also document an unusual September heat wave. The synoptic series is then compared with similar maps previously produced for the more famous 1871 series of firm (8–10 October, including Chicago, Illinois, Peshtigo, Wisconsin, and the same area of Michigan). While the lack of upper-air data precludes a definitive interpretation, both analyses show similar patterns and suggest a basic model for Great Lakes fire-weather forecasting, which includes a steep warm-sector surface pressure gradient as a primary component.

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