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Abstract
Daily average dew points (DADPs) computed for 46 Midwestern first-order stations (FOS) were examined from 1960 to 2000 to identify and characterize extreme warm-season high dew point events. To be classified as an extreme event, more than 50% of the FOS had to experience a DADP of 22°C (72°F) or higher for two or more consecutive days within the event. Nine events were found to have occurred during the 41-year period. The length of the events varied from 5 to 13 days, while the number of stations involved in each event ranged from 24 to 40. Two summers, 1995 and 1999, each experienced two events. Event intensity, based on the percentage of all station hours during each event with dew points ≥ 22°C, was greatest in the events that occurred in the 1990s. An examination of the event diurnal cycle identified that: (1) the minimum number of stations experiencing an hourly dew point value ≥ 22°C occurred at 0300 and 0600 local time, while the maximum number of stations meeting this dew point threshold generally occurred at 0900 and 1200; (2) the biggest dew point increases in terms of spatial coverage of values ≥ 22° occurred between 0600 and 0900; and (3) in 10 of 73 (14%) event days dew points remained ≥ 22°C at ≥ 50% of the stations for 24 consecutive hours. Developing a greater understanding of the spatial and temporal evolution of widespread and intense high dew point events should assist those involved in the design and operation of air conditioning systems that rely on evaporative processes to cool air.
