1995 Chicago heat wave

The 1995 Chicago heat wave was a heat wave which led to 739 heat-related deaths in Chicago over a period of five days. Most of the victims of the heat wave were elderly poor residents of the city, who could not afford air conditioning and did not open windows or sleep outside for fear of crime. The heat wave also heavily impacted the wider Midwestern region, with additional deaths in both St. Louis, Missouri and Milwaukee, Wisconsin.

The temperatures soared to record highs in July with the hottest weather occurring from July 12 to July 16. The high of 106 °F (41 °C) on July 13 was the second warmest July temperature (warmest being 110 °F (43 °C) set on July 23, 1934) since records began at Chicago Midway International Airport in 1928. Nighttime low temperatures were unusually high — in the upper 70s and lower 80s °F (about 26 °C). At the peak of the heat wave, as was the case in the summer of 1988, and possibly 1977, Madison, Wisconsin probably would have broken its all-time maximum temperature record of 107 °F (42 °C) had the reporting station been in the same location as it was during the 1930s.

The humidity made a large difference for the heat in this heat wave when compared to the majority of those of the 1930s, 1988, 1976–78 and 1954–56, which were powered by extremely hot, dry, bare soil and/or air masses which had originated in the desert Southwest. Each of the above-mentioned years' summers did have high-humidity heat waves as well, although 1988 was a possible exception in some areas. Moisture from previous rains and transpiration by plants drove up the humidity to record levels and the moist humid air mass originated over Iowa previous to and during the early stages of the heat wave. Numerous stations in Iowa, Wisconsin, Illinois and elsewhere reported record dew point temperatures above 80 °F (27 °C) with a peak at 90 °F (32 °C) with an air temperature of 104 °F (40 °C) making for a 148 °F (64 °C) heat index reported from at least one station in Wisconsin (Appleton) at 17.00 CDT (22.00Z) on the afternoon of 14 July 1995, a probable record for the Western Hemisphere; this added to the heat to cause heat indices above 130 °F (54 °C) in Iowa and southern Wisconsin on several days of the heat wave as the sun bore down from a cloudless sky and evaporated even more water seven days in a row.

...
Wikipedia