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.

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.

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

A red flag warning for critical fire danger, due to strong winds and low humidity, will remain in effect until 6 p.m. Wednesday for the San Diego County mountains and inland valleys.

The fire threat in Southern California has again reached critical levels, and forecasters have issued a Particularly Dangerous Situation Fire Weather Warning due to dry conditions, low relative humidity and the return of Santa Ana winds.

Firefighters battling the Los Angeles-area fires are facing fresh threats nearly a week after wildfires erupted across the region, fueled by powerful Santa Ana winds in extremely dry conditions. Threat level: The National Weather Service's LA forecast office Sunday evening issued a rare "Particularly Dangerous Situation" Red Flag Warning lasting until Wednesday at noon for parts of L.