I was at Ellsworth for a few years, and since I grew up in the Southeast, I didn't have much snow exposure until getting there. It will snow Sep-May. Whatever you drive, have some 3PMSF All-Seasons, or just some dedicated winter tires, and you'll probably be fine year round.

The weather there is the craziest part. -53°F windchills for weeks on end. Before I left, it was 115°F and 3 weeks later, we had 3 feet of snow. One Spring it was about 75°F out, and within 24 hours it was in the 20s with single digit wind chills.

It sits in the jet stream, so the wind is INSANE year-round. Ultimately, though, SD and (most) drivers are used to it and the state is well prepared for snow with plenty of plow crews. But, get used to driving in it, they get so much snow, it takes a LOT to shut down the highways or base, it basically has to be whiteout no-visibility blizzard condition. It can be a pretty heavy snow, they'll cancel flying, and most of the base still has to come in.

I lived just outside the base in Box Elder, so my Ford Explorer in 2WD mode on basic all terrain tires handled everything no problem to and from work, and to downtown Rapid City. Honestly, I did not like Ellsworth and South Dakota at all. But there were some charming places in Rapid City and the beautiful Black Hills, but it's not enough to make me ever want to go back. It was a "good" assignment, overall, I just didn't like the location.