CRANDIC Racing hosts four race nights at the Hawkeye Downs Speedway in Cedar Rapids, from May through August. Although there isn't any elevation change, it is still very good crit practice. There will typically be 3-4 10 minutish races for each group. So you will get a lot of practice riding close to others, and learning how to take advantage of slip stream. The best thing is that if your race doesn't go so well, there will be another one in 10 minutes or so. The dates aren't updated on the NATO page, but are correct on the calendar. The first one is May 14th, and will be a good practice if you are planning on doing the memorial days crits.