Southwest is sweetening up the holidays with a surprise flash sale! Of course, you'll need to act by tonight if you want to snag a cheap fare. The deals offered through this four-day sale officially disappear at 23.59PT on Dec. 13. What is Southwest offering? If you're lucky, one-way tickets to some pretty impressive destinations can be scooped up for just $39 right now.

Hubs like Boston, Chicago, Denver and Detroit are all on the list of departure cities. The list of available destinations includes everything from Punta Cana to New Orleans. You really just have to dig in to see if any of the featured cities work for your 2020 travel plans.

There are just a few things to know before you grab tickets during Southwest's December flash sale. The fares that are on the table do come with a few restrictions. The big thing to know is that you'll be buying nonrefundable tickets. What's more, Southwest is enforcing some limitations when it comes to travel days, available markets and seats. Both direct flights and single-connection flights are available during the flash sale.

Southwest's December flash sale won't help you if you're looking for cheap tickets you can use to travel during the holiday season. All flight dates are in 2020. However, this sale could offer a way to whip up the perfect surprise vacation for someone on your gift list.

All travel must be done between Jan. 7 and March 4 of next year. Travel between Hawaii's islands is actually valid until May 20 of 2020. There are also some date nuances when it comes to San Juan and other international destinations. It's all spelled out on Southwest's promotional page for the flash sale. The clock is ticking!

Scott Dylan is a contributing writer at GET.com and has been to (almost) every country in North, Central and South America with nothing more than a backpack, a laptop and the desire to explore. He speaks Spanish fluently and has logged enough time in planes, trains, rideshares, buses, taxis and rickshaws to know how to rack up rewards and points to get anywhere his heart desires for pennies on the dollar. Email: scott.dylan@get.com.