A surprise storm dusted parts of Southern California with snow, snarling traffic but delighting many who raced to snap pictures and pack snowballs in the hour before it melted.

Interstate 5 remained closed in the mountains north of Los Angeles on Thursday morning, and jackknifed trucks were stuck in the snow, troopers said.

The fast-moving storm Wednesday was the latest blast from a cold snap that has gripped California for a week.

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At least 18 years have passed since snow last fell in some areas of the Santa Monica Mountains, where beach-bound convertibles are more common than snowplows.

Snow fell at elevations well below 1,000 feet. At architect Doug Rucker's 1,700 feet-high studio in the Malibu mountains, snow was "bouncing like popcorn off my lawns," he said. An hour later, he said, it was "gray mush."

Jen Naylor, an L.A. native, rushed to her sister's house in Westwood, where the backyard was briefly coated in white.

Forecasters said that area was likely blanketed with irregularly shaped hailstones called graupel.

"This was the first time I made a snowman in L.A.," Naylor told the Los Angeles Times. "We used dried cranberry for the eyes and a baby carrot for the nose because it was a baby snowman."