Summary: In the worst tornado outbreak in over half a century, Mississippi and Alabama are ravaged by hundreds of twisters. Towns are wiped clean off the map, and hundreds of people lose their lives.

Summary: On the first chase of the year, there's a storm headed toward downtown St. Louis. While Tim Samaras and his team chase too close to the beast, Reed Timmer's team is on the verge of falling apart.

Summary: After failing to find a twister on two consecutive chases, Reed Timmer and the Dominator team are desperate to chase one down. They're even desperate enough to pursue a powerful storm into an urban area after dark, one of the most dangerous possible chasing scenarios. Team TWISTEX's truck threatens to keep them on the sidelines on a promising tornado day. While team Dominator pursues an intercept, the TIV team is hoping to finally shoot their first ever 3D tornado footage... but tension in the vehicle has everyone on edge, and the crew is finding out that the only thing worse than having a chase ruined by the slick, Texas mud is to be helpless in the path of a tornado.

Summary: In the wake of the deadly and very large tornado outbreak (April 27, 2011), all three chase teams take time to help with the recovery effort. Team Tiv is in Smithville, Mississippi and Team Dominator and Team Twistex are in Tuscaloosa, Alabama. Motivated by the death and destruction they've witnessed, all three teams are rededicated to improving warning times and doing vital research on these deadly storms. Team Dominator fields a new, improved vehicle: the Dominator 2 and tracks a storm right toward one member's childhood home. Team TWISTEX outfits their truck with a brand new probe and a mobile Doppler radar, but mechanical issues threaten to sideline them again. Team TIV adds a mobile tornado siren and chases toward the heart of a twister to warn people while shooting 3D twister footage.

Summary: Reed Timmer and his team take the day off, but when Sean Casey's team scores a victory in Reed's own backyard, the meteorologist vows to chase with a vengeance. Meanwhile, Tim Samaras grows more cautious chasing storms in Kansas.

Summary: A tornado outbreak threatens to wreak havoc in Reed Timmer's backyard. Sean Casey's team follows their navigator's bold prediction, and tension threatens to derail Tim Samaras' chase on a huge day.

Summary: Team Dominator risks everything to warn people in the path of a violent storm, but internal conflicts causes driver Joel to leave, complicating Team Dominator's operations. Still gun shy after witnessing devastation this season, Sean Casey starts to lack the passion of chasing storms, until a visit from his wife and a successful chase reignites Team TIV's fire. Team TWISTEX tries to brave the elements by chasing a tornado through a hail storm, but after their vehicles suffer damage, Tim has to swallow his pride and abandon the chase.

Summary: On the last chase of the season, Reed Timmer's team chases a monster tornado for a radar intercept, and Tim Samaras' team has one last chance to deploy their probe in its path.

Summary: Behind the scenes with cast and crew.