This week Southwest are selling discounted flights across their entire network, valid for travel in the first half of this year. All routes and prices can be seen here.
This deal is open until January 12, 11:59pm Pacific Time. The travel period is January 20 through May 16, and discounted flights are only available on Tuesday and Wednesday. Note also that the following airports are excluded from this offer: Washington D.C. (Dulles); Ft. Myers, FL; Seattle, WA.
Southwest do not allow their flights to be listed on comparison websites like CheapAir, so you’ll need to book tickets directly at their website.