Most chasers do not actively pick the Northern Plains as their primary targets for storm chasing and typically go chasing earlier in the season when there are more chances for severe weather in states like Texas, Oklahoma and Kansas. If you go chasing in June and July, you are quite likely to be chasing in the Northern Plains and that is definitely not a bad idea – especially if you are more into photography!
The Northern Plains may not have the same frequency of tornadoes as the Southern/Central Plains but they are by no means rare – especially in certain areas like the South East corner of Wyoming, Nebraska and parts of South Dakota. Nebraska is known for some incredible tornado outbreaks and perhaps the most memorable tornado event ever in Pilger, NE, when there were two EF-4’s on the same storm.
What the Northern Plains offers is also an incredible natural beauty that the flatlands of the southernmore States cannot match. The drives between storms in areas like western Nebraska, South Dakota, central Eastern Wyoming are just incredible! The possible lack of moisture cause storms to be more on the high-based side which can give you some spectacular tall tornadoes and amazing LP supercells! If you are into photography (over adrenaline), choose the Northern Plains!
It should also be noted that there are Canadian tours (like Tornado Hunters) based out of Canada that are suitable for chasing the Northern Plains (and Canada as well). In addition COD offers tours out of Chicago which is also closer to the Northern Plains.
Storm chasing is, by its nature, not geographically set: you go where the storms are. If you specifically want to chase a setup in the Northern Plains or if you would like to chase the storms that exist in those stats on a specific day your best option is to try a Private Tour. Very few are based in those states though so you may have to cut a deal to meet up and fly into airports like Rapid City or Omaha.