The National Weather Service’s Aviation Weather Center (AWC) has issued an alert flagging the presence of severe turbulence in the air over southern Lake Michigan, northern and western Michigan, northwestern Indiana, much of northern Illinois, parts of southeastern Wisconsin, and portions of southeastern Iowa. Air travel in and out of Chicago O’Hare Airport (ORD) is one example of many airports being impacted by this alert. The nation’s three largest airlines, American Airlines, Delta Airlines, and United Airlines all have a significant presence in this market with many of their flights impacted; United is impacted by far the most since they operate 45% of all flights in/out of the airport there as part of their Chicago hub operations.
Specifically, SIGMET YANKEE 2 has been issued through at least 0315Z Tuesday.
According to the AWC, there is occasional severe turbulence between 25,000 feet and 35,000 and this is due 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, with injuries encounter on two U.S. airline flights last week.
A week ago today, a United Airlines 767 jet encountered severe turbulence on its flight to Houston, Texas. Due to that encounter with rough air, 3 crew members and 2 passengers had to be rushed to the hospital for care upon landing.
The day before, on December 18 , 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, some with serious injuries.
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.