The National Weather Service’s Aviation Weather Center (AWC) has issued an alert flagging the presence of severe turbulence in the air over a large part of the western United States including large parts of California and Nevada, much of Oregon, southern Washington, and western Idaho.
Air travel in and out of Las Vegas’s McCarran Airport (LAS) is one example of many airports being impacted by this alert. Air travelers coming from the east into west coast cities such as Portland (PDX), San Francisco (SFO), Los Angeles (LAX), and San Diego (SAN) would also be impacted by this alert as well as all east-bound flights from those cities.
Specifically, SIGMET NOVEMBER 5 has been issued through at least 2356Z tonight.
According to the AWC, there is occasional severe turbulence below 18,000 feet due to strong low level winds and wind shear. 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 Monday, 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.