Trade fairs, conventions and regional sporting events can also havoc with prices. Further, bear in mind that the wonder of the internet is that all the carriers can also see what 'striking' prices are being listed by each other - all the time. If they want to make sample bookings to see what prices they are competing with, they can do it every hour. This tends, in my view, to push prices up, not down.
May I suggest that, when looking at prices, also look carefully at the indirect routings? For example, you might discover an indirect that enables a long weekend somewhere you haven't been and is better priced. Since most folks want to go direct between 'city pairs' they cost more. Or not, if any of the above mentioned factors come into play!!