"New global warming research suggests that the Midwest will be slightly cooler in the future than neighboring regions of the United States.
The predicted "hole" in the blanket of warmer temperatures comes from the cooling effect of increased rainfall, cloud cover and evaporation, said Zaitao Pan, an atmospheric scientist at St. Louis University."
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"According to the study, moist air from a warmer Gulf of Mexico will drop more precipitation on the Midwest in the next 40 to 50 years. Water absorbed by the soil will evaporate, creating a shady cloud cover and reducing summertime air temperatures."
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"Weather patterns over the past 25 years show that the Midwest is already experiencing the "warming hole," the researchers said. After looking at predicted changes, the team reviewed peak temperatures from 1975 to 2000 and discovered a slight cooling in an area that includes parts of Kansas, Missouri, Oklahoma and Iowa."
http://www.stltoday.com/stltoday/news/stories.nsf/stlouiscitycounty/story/698D4CC0A543973386256F17001A9EF9?OpenDocument&Headline=Midwest+will+be+slightly+cooler+than+neighbors,+study+sugges&highlight=2%2Cmidwest%2Ccooling(Sorry about the long link)
This jives with my experience here. Summers have been hot, but not unusually so, like many other parts of the country.