Southwest Airlines flash sale includes roundtrip flights for under $100

(Woodys Aeroimages/Flickr)

The big Southwest Airlines sale is back - and you can get out of town this summer and this fall for less than $50.

Southwest is holding their 72-hour sale in which some round-trip tickets cost just $49 from Detroit. Southwest Airlines holds this three-day sale twice a year, and they just launched the latest one Tuesday morning.

Fares start at $49 each way and go up to $129 for longer flights.

From Detroit, you can get to Baltimore and Chicago for $49 one-way. You can get to Nashville and St. Louis for $79, and you can get to Denver for $99. 

The sale is good for domestic travel between August 20 and December 18 of this year, but you can't travel on Fridays and Sundays. 

For international travel destinations and Puerto Rico, the dates vary.

Southwest holds this big sale twice a year - in the late spring and again in October. 

There is a bit of fine print you would want to know. Aside from the rates only being available during the weekdays, there are black out dates of August 30 and September 2 (Labor Day weekend) and November 22 through December 2 (Thanksgiving). 

Plus, you've got taxes and fees to pay too - so it's a little more than $49, but not much.

Either way - it's cheaper than usual. If you're ready to get out of town, you have until Thursday to book and get a deal.