Book flights by Thursday, January 27, on Southwest Airlines to take advantage of discounted one-way fares such as $29 (example: Los Angeles-Las Vegas), $41 (Boston-Baltimore), $86 (Nashville-Panama City Beach), and $99 (St. Louis-Philadelphia). A 14-day advance purchase is required, and travel is valid through May 21. Flights on Fridays and Sundays are more expensive, and there are a few blackout dates.