Northern Plains??
Do you also mean Northern Rockies, too?
Also - when you say "next couple of months" that can mean different things.
Last year was a record snowfall year and long winter.
Roads in national parks and mountain passes can close as early as late September.
Although there can be nice days in October, there can also be blizzards.
If you plan to be riding in Idaho/Montana/Wyoming in October -
you should opt for the lowest crossings possible.
Possibly US 12 to Missoula, MT 200 east into the Plains.
If you have never done it, you should absolutely ride Going to the Sun Road in Glacier National Park.
(But be aware that it will close for contruction some time after Labor Day.)
http://www.nps.gov/glac/planyourvisi...thesunroad.htm