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 California and Nevada as well as parts of Utah and Arizona. An onslaught of stormy weather which continues to batter the West Coast with storm after storm in an ongoing Atmospheric River event has produced a variety of hazards. Conditions were even ripe last night for tornadic thunderstorms, which triggered the issuance of Tornado Warnings for portions of California east of San Francisco’s Bay Area. Now the same atmospheric set-up is creating severe turbulence in the air, making air travel hazardous for those flying through the warning area.
Air travel in and out of Los Angeles Airport (LAX) and Las Vegas’s Harry Reid International Airport (LAS) are two examples of many airports being impacted by this alert. Air travelers coming from the east into west coast cities such as San Francisco (SFO) and San Diego (SAN) would also be impacted by this alert as well as all east-bound flights from those cities.
Specifically, SIGMET ROMEO 18 has been issued through at least 2203 UTC tonight.
According to the AWC, there is occasional severe turbulence below 20,000 feet due to strong low level winds, mountain waves, strong updrafts and downdrafts, and low-level 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. In recent weeks, two U.S. airline flights encountered severe turbulence which landed dozens of crew and passengers into the hospital.
In the days before Christmas, 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.