Today is the 15th anniversary of the devastating F5 tornado that tore through Moore, Bridge Creek, and Newcastle in Oklahoma on May 3, 1999. The tornado remains the strongest ever observed (a Doppler-on-Wheels measured winds of 301 MPH) and the analog to which all major tornadoes were compared up until Joplin in 2011. Over ten thousand structures were damaged or destroyed in the storm, and three dozen people lost their lives.
The storm is also notable for being the first time that meteorologists at the National Weather Service used the term "tornado emergency" in a tornado warning. The enhanced wording was used to convey the severity of the situation to those in the twister's path, and later became convention when a large tornado was confirmed and moving towards a populated area.
Above is an "as it happened" clip from KFOR in Oklahoma City, covering the storm as the tornado as it came through the affected towns. Oklahomans have a long tradition of chasing tornadoes with helicopters, something that multiple stations did in 1999 and continue to do today.