The marine layer can make flying difficult. Here are a few key facts about the coastal weather phenomenon

marine layer

The helicopter crash that killed Kobe Bryant and eight others happened on a morning when there was a significant marine layer, which may have contributed to difficulty in navigating the helicopter.

The marine layer is well-known to Californians as the reason why you need a big down vest when you’re walking through Golden Gate Park during the summer, or why Santa Monica can be gloomy and cold in May and June. “June gloom,” Californians will murmur as they shuffle into their coats, start up their cars, turn on their headlights, and begin to drive through the gray at 6am. In fact, contrary to the myth that the Golden State is always sunny, many Californians are more likely to put on a warm coat in summer than in winter, especially near the beach.

Here are a few facts about the marine layer.

Think of It as a Trapped Air Bubble

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Though it’s officially an “air mass,” the marine layer could be conceptualized as a kind of bubble that is trapped. This special weather phenomenon only happens above bodies of water like oceans or large lakes, so it’s a California thing—that’s why San Francisco-based fashion label Marine Layer brings up images of the beach. When the ocean below cools the warm air above and thickens it, the cooling air bubble is trapped below warmer air above. That means that though it’ll be cold below the marine layer, it can often be warmer above the marine layer—say, in a mountain range peeking above it.

A Marine Layer Is Not (Quite) the Same Thing as Fog

A marine layer can contain fog, which is visible, low-lying condensed air containing water drops or ice crystals—essentially, a cloud close to the ground. But it’s not actually fog, it’s more the Tupperware that holds the fog. Fog happens everywhere, but marine layers are special because they only occur where there are large bodies of water, and they can keep fog around longer, trapping it.

The Marine Layer Is a Morning Person

The marine layer peaks at sunrise, and wanes as the day goes on. Bryant’s fatal helicopter crash occurred around 9:45am, nearly a few hours after the 6:56am sunrise in Calabasas (the location of the crash). The marine layer is also most present during the May to October months, but can appear at any time.

Flying Can Be Difficult With a Thick Marine Layer

The marine layer can make navigation difficult and disorienting. The LAPD and the Los Angeles County Sheriff’s Department had both grounded their helicopters the morning when Bryant’s helicopter crashed. When relying on navigational guidance and controls with low visibility due to the marine layer, an emergency can be difficult to handle.

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