I've also found that fares on CO will go up on Mon/Tues, then be lower the latter part of the week. This is anecdotal, so I'm not sure as to the pattern, but the last ticket I purchased was like this. I checked on Thurs & Fri and it was low. When I checked again Mon it had spiked, same Tues. On Wed it was back down to Fri's low fare and I grabbed it. Interesting.