We were returning home from Colorado Springs via DEN and FLL. A couple of hours later we were evacuated from our about-to-depart Southwest flight because the Denver airport came under a tornado warning from a storm coming in from over the mountains west of Denver. All passengers on aircraft at the terminals, plus those in the terminals, were evacuated into designated tornado shelters. Consequently we departed over an hour late and arrived at FLL at 1am which made for a long day.