Much of Minnesota will be under an extreme heat warning Monday as temperatures climb into the mid-90s. With combined temperatures and dew points in the 70s, heat index values are expected to reach or exceed 105 degrees, according to the National Weather Service. The extreme heat warning is in effect from 9 a.m. to midnight Monday, June 29, in portions of central, west-central and southwest Minnesota, according to the Weather Service. Hot and hum…