The states where climate station data shows the greatest amount of warming include Montana, North Dakota, South Dakota, Minnesota, Wisconsin and Michigan.

Studies on the seasonal timing of snowmelt with earlier runoff into rivers in the North Central region in recent decades, agree with the temperature warming trends shown, and both temperature and snowmelt trends indicate
North Central amplification of warming in the U.S.

From my perspective, personal and professional in hydrology,

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 http://npat1.newsvine.com/_news/2007/01/21/530108-temperature-and-snowmelt-data-in-minnesota-and-wisconsin-show-recent-warming-amplification-in-north-central-us


 http://npat1.newsvine.com/