The National Weather Service’s Aviation Weather Center (AWC) has issued a SIGMET alerting pilots and passengers of the threat of severe turbulence in the airspace over portions of Kentucky, Ohio, Illinois, West Virginia, and Virginia. Specifically, SIGMET NOVEMBER 1 has been issued through 0045Z this evening.
According to the National Weather Service, there is occasional severe turbulence in the SIGMET area between 18,000 feet and 31,000 feet, altitudes typically used by commercial aircraft flying through this region. The National Weather Service says this severe turbulence is being created by wind shear associated with the jet stream. Wind shear is a difference in wind speed and/or direction over a very short distance in the atmosphere. Airline pilots generally regard significant wind shear to be a horizontal change in airspeed of 30 knots (15 m/s or 34 mph) for light aircraft and 45 knots (23 m/s or 51 mph) for traditional airliners flying at flight altitude.
Flying through turbulence can be dangerous. Yesterday, Hawaiian Airlines Flight 35 flew through severe turbulence before landing at Honolulu International Airport after originating in Phoenix, Arizona. A Mass Casualty Emergency Event was declared, with dozens of passengers needing care for injuries sustained in the violent ride. Officials with Honolulu Emergency Medical Services and American Medical Response say the flight encountered the extreme turbulence about 30 minutes prior to landing; they treated 36 patients at the airport. 20 patients, ranging from a 14-month old toddler to older adults, were transported to hospitals near the airport. 11 are in serious condition while 9 are in stable condition, with patients spread out in multiple emergency rooms.
Known as a SIGMET, short for Significant Meteorological Information, the severe weather advisory issued by the AWC contains weather-related information concerning the safety of all aircraft passing through a specific zone. Sometimes AIRMETs are issued too; an AIRMET consists of turbulence, visibility, and icing-related warnings that are less severe than those in a SIGMET.