(NewsNation) — Within the past week passengers on two major airlines have been injured after mid-flight turbulence and many holiday travelers are wondering if severe winter weather is about to make things worse.

On Sunday, dozens of passengers were injured after a Hawaiian Airlines flight going from Phoenix to Honolulu hit severe turbulence. In total, 11 people were seriously injured and nine others had minor injuries.

Just one day later, at least five people were injured after a United Airlines flight from Rio De Janeiro, Brazil, to Houston experienced unexpected turbulence.

Despite the widely reported incidents this week, serious injuries from airplane turbulence are extremely rare.

Since 2009, 146 people have suffered “serious injuries” from turbulence on airplanes, according to the Federal Aviation Administration (FAA).

Last year, six people — one passenger and five crewmembers — suffered serious turbulence-related injuries — about one serious injury for every one million flights in 2021.

Over the past decade, no single year has seen more than 18 turbulence-related serious injuries. Data shows crewmembers are the most commonly injured, accounting for about 80% of those hurt in recent years.

As a proportion of air carrier accidents, turbulence is the most common cause. A 2021 report from the National Transportation Safety Board revealed more than one-third of air carrier accidents in the U.S. involving serious injury are due to turbulence.

The FAA doesn’t track general incidents of turbulence that don’t result in injuries but data from the National Center for Atmospheric Research suggests turbulence itself is quite common.

“The number of pilot-reported encounters with turbulence is substantial: over the US, moderate-or-greater pilot reports (PIREPs) average about 65,000/year, and severe-or-greater PIREPs average about 5,500/year,” according to the National Center for Atmospheric Research.

In other words, the vast majority of turbulence events don’t result in injuries of any kind.

With a severe winter storm in the forecast, many people are wondering whether their holiday flights will feel more bumps along the way.

Although it’s normal to associate turbulence with stormy weather, clear-air turbulence (CAT) is often the most dangerous. It is most common during the winter, but again, injuries are exceedingly rare.

As the name suggests, CAT can happen when the sky looks clear, which makes it difficult to detect. Without early warning, passengers are more likely to be out of their seats when clear-air turbulence hits and that can cause injuries.

In the case of severe thunderstorms, pilots may try to avoid dangerous conditions altogether.

Jon Snook, the chief operating officer for Hawaiian Airlines, said the fasten seat belt sign was on as the plane headed into bad weather this week, but even then the turbulence came as a surprise.

“There was no warning of this particular patch of air at that altitude was in any way dangerous,” said Snook. “It caught everybody by surprise, which is often the case.”