Weather Explainers

In California, 'June Gloom' Is a Real Thing

At a Glance

The California coast often experiences "June gloom" in early summer.
Low clouds and fog might make your beach day less than ideal in SoCal.

Most people associate June with summertime – sunshine and warm temperatures. And for much of the country, this is typically the weather that occurs in summer's first month.

But this isn't the case for parts of the California coast; if you're planning to visit early in the summer, don't forget your jacket.

Along the coast of the Golden State, there's a "June gloom" – low clouds and fog during the morning hours, which usually burn off midday or early in the afternoon.

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Layers of blue sky, fog bank, sandy beach and ocean waves. — In this file photo, beach-goers in Santa Monica, California, don't let low clouds and fog ruin their day.
(Denise Taylor/Getty Images)

Intense heating of inland areas, such as the Central Valley and Mojave Desert, sets up a broad area of low pressure known as a thermal low.

With high pressure over the Pacific Ocean, a pressure gradient develops and pushes the cooler ocean air inland. If this marine layer is deep and moist enough, low clouds and fog are the result.

The National Weather Service in San Diego posted on Facebook that May features only 59 percent of possible sunshine, and only 58 percent of possible sunshine occurs in June, based on averages at San Diego International Airport.

"It's worth pointing out that most locations away from the coast, especially more than 10 miles or so inland, do not see nearly the impact as locations along the immediate coast," the NWS added. "Conversely, the SoCal beaches will see even less sunshine, on average, than the airport location."

Therefore, it's best to sleep in and wait until the afternoon to head to Southern California's beaches, especially in early summer.

This NASA Worldview visible satellite image shows low clouds and fog along the coast of Southern California on May 30, 2017.
(NASA)

Farther north, in the San Francisco Bay Area, low clouds and fog are also common in the morning, but strong winds through the Golden Gate Bridge typically mix out the marine layer by the afternoon.

A common sight along the California coast in spring and summer is a coastal eddy, in which the low stratus cloud deck takes on the shape of a hurricane.

"We see them on a regular basis," Jan Null, a Bay Area-based certified consulting meteorologist and former lead forecaster at the NWS in Monterey, California, told weather.com. "During the summer, we'll see at least one a week if there's a stratus field."

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April through September is when these types of eddies are very common along the coast of California, the NWS in Monterey said.

Brian Donegan is a digital meteorologist at weather.com. Follow him on Facebook and Twitter.

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