It could be there's something going on in CLE during that time that they're expecting high volumes for so they'll up the price for that destination. When I needed to be ~2.5 hrs north of DTW for meetings in February last year, the price from IAH-DTW was over $600 on NW. However, if I went IAH-DTW-MBS-DTW-IAH it was under $300. It was obvious they were just gouging everyone going to DTW for Super Bowl activities.