LOS ANGELES (CBSLA) — A dense fog advisory for parts of the San Fernando Valley and much of the Inland Empire will make for a perilous Friday morning commute.

The National Weather Service says the dense fog advisory will be in effect until at least 9 a.m. throughout Woodland Hills, Northridge, Burbank and Universal City, with visibility down to a quarter mile or less.

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Dense fog covered most of Ventura Boulevard in the west San Fernando Valley, and obscured street signs.

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A much bigger patch of fog stretched from San Bernardino, across Riverside and into parts of Orange County.

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In foggy conditions, drivers were advised to reduce their speeds, increase following distance and use low beam headlights.