We have similar issues here in Regina. University break week here in 2012 is February 18-25. Air Canada's fares were high for that week the moment the schedule for then was released (i.e. almost a year in advance). They know darn well that it's a popular week for flying out of Regina and they charge accordingly. Eventually they fill all their seats.

Delta and United start with more moderate fares. Once they hit a certain threshold of load factor for the flights, they bump up their fares and eventually they are as high as Air Canada is (or higher). However, if you buy early enough you can do better with them than you can with Air Canada.

Ultimately it's all down to supply and demand. If you want low fares, you have to go when fewer people travel and if you want to travel when many others are travelling, you have to endure higher fares. I've seen screamingly cheap fares for Christmas Day departures, but the day before and the day after are typically horrible. Reason: People want to leave no later than the 24th and depart no earlier than the 26th, so there is pressure on those days. Hardly anybody wants to actually fly on Christmas Day so the demand is a lot lower.