What do ‘Red Flag Warnings’ mean?

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Diane Sieker photo

Anyone who has lived in Southern California for any length of time has heard the term “Red Flag Warning.” But exactly what does the alert mean for the average resident?

The National Weather Service said, “A ‘Red Flag Warning’ is used to warn of an impending or occurring Red Flag event. Its issuance denotes a high degree of confidence that weather and fuel conditions consistent with local Red Flag event criteria will occur in 12 to 24 hours or less. Forecasters can issue the watch or warning for all or selected portions within a fire weather zone. The Red Flag event is verified when the weather and fuel conditions listed below are met simultaneously for any three hours or more during the period. The warning should remain in effect until the critical fire weather pattern ends.”

Weather and fuel conditions that are forecast to occur or can already be happening before issuing a Fire Weather Watch or Red Flag Warning include minimum relative humidities equal to or less than 15%, winds of 20 mph or higher or gusts to 35 mph or higher. These watches and warnings are most likely to be posted during Santa Ana wind events, where powerful, dry winds pummel southern California during the autumn months.

The National Weather Service defined Santa Ana winds as strong down-slope winds that blow through the mountain passes in southern California. These winds – which can easily exceed 40 miles per hour, with isolated gusts as high as 70 mph in narrow passes – are usually warm and dry and can severely exacerbate brush or forest fires, especially under drought conditions. Being the end of the dry summer and before the winter rains, fall is an exceptionally dangerous time for wildfires to start and get out of control.

These powerful wind events can bring the lowest relative humidities of the year to affected areas. These conditions combine with a warm, compressionally heated air mass, plus high wind speeds, and create critical fire weather conditions. The Santa Anas are blamed for causing countless regional wildfires to become extremely large, destructive and life-threatening.

“With some of the most destructive and deadliest fires occurring from October through December, we need Californians to not be complacent,” Cal Fire Chief Thom Porter said. “Wind-driven fires move fast, and residents need to be ready to evacuate at a moment’s notice in the event of a wildfire. We have increased our staffing but need the public to remain vigilant. It is important to follow evacuation orders and leave early as fires move very fast under these conditions.”

Porter stressed the need for people to take basic preventative steps, such as not mowing lawns during high winds, not driving vehicles over extremely dry vegetation, where sparks or hot engine components might touch off a blaze, limiting campfires to designated places and being on the lookout for suspicious behavior that could be arson-related.

Caltrans District 8, which serves the inland region, advised motorists that light signals could go out if utilities implement public safety power shut-offs, which are permitted by the California Public Utility Commission. Officials said flashing and blacked out traffic signals must be treated as stop signs, with the usual right of way and yielding protocols in place.

The PSPS, or de-energizations, are permissible during high fire danger to prevent electricity lines from arcing or transformers from throwing sparks and igniting fires, particularly in places not easily accessible to firefighters.

Southern California Edison, which serves large parts of Riverside County, has a policy of generally trying to notify customers two days in advance of a prospective shut-off during a Red Flag Warning.

Anza Electric Cooperative Inc. general manager Kevin Short said, “A Red Flag Warning, as posted by the National Weather Service, puts all electric utilities on high alert for the danger of fire. Strong winds can bring trees or other debris into our lines, raising the threat of ignition. We are on a constant lookout for these conditions, and take extra care to maintain our system in top condition to mitigate risk. The safety of our community and our employees is always our primary concern.”

AEC’s imported power is carried on Edison’s lines and can be affected by a PSPS issued by Edison.

People need to be prepared. From stashing emergency supplies, having evacuation plans, to maintaining fire safe perimeters around homes and abating weeds in a safe manner, living in fire country demands awareness.

Southern California is battered yearly by the Santa Ana winds, and residents have learned to pay special attention to the Red Flag Warnings that accompany them.

Diane Sieker can be reached by email at dsieker@reedermedia.com.