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.

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.

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.

"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 has been issued through Wednesday in Southern California because of potentially dangerous fire conditions.

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 ...

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 ...

As last week’s infernos still blaze in Los Angeles, the National Weather Service issued a Red Flag fire warning for portions of San Luis Obispo County on Monday.