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Saturday, July 7, 2012

Jeff Masters: Heat wave breaks more all-time records in Midwest

Heat wave breaks more all-time records in Midwest

by Dr. Jeff Masters, Wunderground blog, July 7, 2012

The extraordinary heat wave of late June-early July 2012 toppled more Dust Bowl-era records on Friday, with three cities in Michigan hitting their hottest temperatures ever recorded. Lansing hit 103 °F, the hottest day in Michigan's capital city since record keeping began in 1863. Lansing has hit 102 °F four times, most recently on July 24, 1934. Muskegon, MI, hit 99 °F, matching that city's record for all-time hottest temperature set on August 3, 1964. Records go back to 1896 in Muskegon, which has never hit 100 °F, due to the cooling effect of nearby Lake Michigan. Holland, MIhit 102 °F, Friday, tied for hottest temperature in city history. Grand Rapids, MI, hit 104 °F, Friday, the third hottest temperature in city history. Only two readings during the great Dust Bowl summer of 1936 were warmer: 108 °F on July 13, 1936, and 106 °F on July 12, 1936.

Figure 1. Water temperatures averaged over Lake Michigan are running 11 °F (6 °C) above average so far in 2012. Image credit: NOAA/GLERL.

Chicago's third consecutive 100 °F+ day ties record for longest such streak
Chicago, IL, hit 103 °F, Friday, which was just 2 °F shy of their official all-time high of 105 °F set on July 24, 1934 (the unofficial Midway Airport site recorded 109 °F on July 23, 1934, though). Friday was the third consecutive day with a temperature of 100 °F or hotter in Chicago, tying the record for most consecutive 100-degree days (set on July 3-5, 1911, and Aug 4-6, 1947). Historically, Chicago has 15 days per summer over 90 °F and one day every 2.3 years over 100 °F. Under a higher-emissions scenario, climate change models predict that Chicago could experience over 70 days above 90 °F by 2100 and 30 days over 100 °F. With summer less than half over, Chicago has seen 18 days over 90 °F and 4 over 100 °F in 2012. The record number of 100 °F days in Chicago is 8, set in 1988. The heat wave in Chicago comes at the end of a nine-month period of record warmth in the city, including the warmest March on record. As a result, Lake Michigan has heated up to the warmest levels ever seen this early in the year. Temperatures of 80 °F -- fifteen degrees above average -- were measured at the South Buoy on Lake Michigan on Friday. 

Figure 2. Climate models predict many more hot summers like 2012 ahead for Chicago. Image credit: Union of Concerned Scientists.

Historic heat wave in Indiana
"The Indianapolis area is nearing the end of an historic heat wave, the likes the area has not seen in 76 years," said the Indianapolis National Weather Service on Friday. To make matters worse, current drought conditions are worse than during the Dust Bowl of the 1930s. The only times less rain fell from May 1-July 5 were 1988 and 1895. Indianapolis hit 105 °F, Friday, which was just 1 °F shy of their official all-time high of 106 °F set at the official downtown site on July 14, 1936, and July 25, 1934. (The unofficial airport site recorded 107 °F on July 25, 1934.) Historically, Indianapolis has 17 days per summer over 90 °F and less than one day over 100. Under a higher-emissions scenario, climate change models predict that Indianapolis could experience over 80 days above 90 °F by 2100, and 28 days over 100 °F. With summer less than half over, Indianapolis has seen 20 days over 90 °F and 5 over 100 °F so far in 2012. Only the years 1936 and 1934 had more 100 degrees days: 1936 with 12, and 1934 with 9.

Figure 2. The severe weather map for Saturday, July 7, 2012, had advisories for extreme heat (pink colors) for portions of 26 states.

The forecast: more record heat Saturday, then relief
More record-breaking triple-digit heat is expected Saturday across much of the Midwest and Tennessee Valley. All-time highs in Washington, DC (106 °F), Pittsburgh (103 °F), Indianapolis (106 °F), and Louisville (107 °F) may be threatened. However, sweet relief is in sight. A cold front will move southwards out of Canada on Saturday and Sunday, putting an end to this phase of the great heat wave of 2012. By Monday, temperatures will be near average for most of the eastern 2/3 of the U.S., and will remain near average for the entire week.

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