Don't wait until the last minute. Tomorrow's flight may cost a lot more than the same one next month. Avoid Holidays Easier said than done, but work around them if you can. This resource gives quick status reports for USA and Canada flights.
Check departures as well as arrivals, delays, schedule changes.
This is the official government control center site that gives you a map of the United States where you can click on the city of your choice to see airport closures or delays.