May 31, 2013 tornado system that went over the Oklahoma City area through an extremely densely populated area of El Reno in Canadian County; the EF4 tornado that hit Beauregard, Alabama on March 3, 2019, the EF4 tornado that affected western portions of the Kansas City area on May 28, 2019 and the EF4 tornado that affected several areas in Mississippi on April 12, 2020. This enhanced form of a tornado warning is issued mainly by Weather Forecast Offices within the National Weather Service's Central and Southern Region Headquarters; a tornado emergency is the highest level of a three-tiered Impact Based Warning system for tornadoes used by all WFOs within the Central Region Headquarters, and eight others within the Eastern, Southern and Western Regions. Severe thunderstorm watch (SVA; pink box or blue box in NWS documents, typically yellow box in other media) – Conditions are favorable for the development of severe thunderstorms in and close to the watch area. A severe thunderstorm contains large damaging hail of diameter or larger, and/or damaging winds greater than 58 mph (95 km/h or 50 knots) or greater. Isolated tornadoes are also possible (depending on whether atmospheric conditions are sufficient to produce tornadic activity) but not expected to be the dominant severe weather event. These watches are issued for large areas by the Storm Prediction Center in Norman, Oklahoma, and are usually valid for five to eight hours. Particularly dangerous situation severe thunderstorm watch (SVA) – Conditions are favorable for the development of severe thunderstorms in and close to the watch area. Isolated tornadoes are possible but not expected to be the dominant severe weather event, hence these watches are very rarely issued. An expected severe wind event (derecho) is the mostly likely reason for a PDS severe thunderstorm watch to be issued, with widespread winds greater than 90 mph (150 km/h or 80 knots) possible. These watches are usually valid for a longer period of time and are issued for a larger area by the Storm Prediction Center in Norman, Oklahoma than a typical severe thunderstorm watch. This type of watch is usually only reserved for forecast "high-end" severe weather events. If, however, tornadoes are expected to be a major weather threat in addition to the preceding criteria, then a standard tornado watch (generally not a PDS watch) would be issued instead. Severe thunderstorm warning (SVR) – A severe thunderstorm is indicated by