With AM radio signals, the solar radiation keeps the radio signal under control, at night the station has to power down. Many stations, like KFGO, have to point the antenna to a specific direction to avoid interfering with other stations (at lower frequencies the signal can travel hundreds of miles). That's why you can hear WCCO at night, they don't have to power down or go directional.
I know Lakes will hate the lack of coverage into Minnesota but that is a pretty good signal pattern for ND.
KFGO Daytime signal http://radio-locator.com/cgi-bin/patg?id=KFGO-AM&h=D
KFGO Nighttime signal, showing a directional pattern http://radio-locator.com/cgi-bin/patg?id=KFGO-AM&h=N
That's why they drop out in the lakes area around sundown.