Complex sentence: Braniff dispatchers were aware that their flight 255 had delayed departing Sioux City for Omaha by one hour to allow the storm to pass Omaha; they also knew that their flight 234 from St. Louis to Des Moines had diverted to Kansas City due to the storm.
Split into simpler sentences: Braniff dispatchers were aware that their flight 255 had delayed departing Sioux City for Omaha by one hour to allow the storm to pass Omaha. Also that their flight 234 from St. Louis to Des Moines had diverted to Kansas City due to the storm.