Red flag criteria is generally when relative humidity is at 15% or less, combined with sustained winds and/or gusts of 25 mph or greater. Both of these conditions must occur simultaneously for at least 3 hours in a 12 hour period, according to the NWS.

Red flag warnings tell other agencies, like fire and transportation departments, that it's time to staff up and prepare to respond to fast-moving fires. But they're also intended to put the public on high alert.

The most serious red flag fire weather warning has been issued by the NWS for swaths of L.A. and Ventura counties starting before dawn Tuesday.

"If fire ignition occurs, conditions are favorable for very rapid fire spread and extreme fire behavior," the NWS warns.

As firefighters struggle to gain control of massive and deadly wildfires that are raging across parts of the Los Angeles area, the region is once again bracing for the potential of new fires and for current ones to intensify as a new storm system heads for the state.

Californians in the greater Los Angeles area have been on edge due to high winds and dry conditions. The Palisades and Eaton fires have killed at least 25 and destroyed thousands of homes.

A red flag warning for Wednesday has been issued for Southern California as concerns about the fast-growing wildfires increasing.

Correction and clarifications: A previous version of this story incorrectly said the city of Palm Springs would be included in the Red Flag warning. The National Weather Service has issued a Red ...

A red flag warning has been issued through Wednesday in Southern California because of potentially dangerous fire conditions.

SAN DIEGO (FOX 5/KUSI) — The National Weather Service has issued a Red Flag Warning for most of eastern San Diego County amid another round of Santa Ana winds. NWS on Sunday said Santa Ana winds ...

LOS ANGELES - The red flag warning may have temporarily expired for Southern California, but Angelenos are far from being out of the woods. As residents across Los Angeles County continue to deal ...

Friday, 4:50 p.m. PST Cal Fire reported 31% containment on the 23,713-acre Palisades Fire, meaning firefighters now have control of about one-third of the perimeter of the fire; Cal Fire also reported 65% containment for the Eaton Fire and full containment of the Auto and Hurst fires.