Red Flag Warning
Explained
A Red Flag Warning doesn't mean a fire is burning — it means conditions are lined up to make any fire spread fast and hard to control. Here's what triggers one and what to actually change about your day.
What Is a Red Flag Warning?
A Red Flag Warning is issued by the National Weather Service when weather conditions create an increased risk of fire danger. It's a forecast product, not a report of an active fire — it means the atmosphere itself has become the hazard.
The warning is typically issued 12–24 hours ahead of the conditions arriving, giving fire agencies and residents time to prepare. A less urgent version, a Fire Weather Watch, may be issued a day or two out when conditions look likely but aren't yet certain — the same relationship as a tornado watch vs. warning.
The Three Ingredients
NWS fire weather offices issue a Red Flag Warning when a specific combination of conditions is expected, though exact thresholds vary by region:
Low Relative Humidity
Typically 15–25% or lower. Dry air pulls moisture out of vegetation, turning it into ready fuel.
Sustained Wind
Typically 15–25+ mph sustained, often with higher gusts. Wind feeds oxygen to a fire and carries embers well ahead of the flame front, starting new spot fires.
Dry Fuels
Grass, brush, and timber that have dried out from drought or seasonal curing. Fire behavior specialists track fuel moisture separately from the weather forecast to confirm this condition is met.
All three together — not any one alone — is what pushes a forecast office to issue the warning.
What to Actually Do
Don't Create a Spark
No outdoor burning, no fireworks, no welding or grinding outside, no dragging trailer chains. Avoid parking on dry grass — a hot catalytic converter can ignite it in minutes. Most wildfires during Red Flag conditions are human-caused.
Prep Your Property
Clear dry leaves and debris from gutters and around the foundation. Move firewood stacks and propane tanks away from the house. Know your defensible-space zone if you're in a wildfire-prone area.
Have an Evacuation Plan
Know two routes out of your neighborhood. Keep your car fueled and important documents accessible. If local officials issue evacuation orders, don't wait to see the fire yourself before leaving.
Where Red Flag Warnings Matter Most
Red Flag Warnings are most common in the wildland-urban interface — areas where homes border grassland, brush, or forest — across California, the Pacific Northwest, the Southwest, and the southern Plains. Some of the most destructive wildfires in US history, including several major California fires, started or spread explosively during Red Flag conditions, when a single spark from equipment, a vehicle, or a downed power line met exactly the wind and dryness the warning describes. Utilities in fire-prone areas increasingly use these warnings to trigger Public Safety Power Shutoffs — deliberately cutting power to reduce the risk of equipment sparking a fire.
Get Fire Weather Alerts on Your Phone
StormCast pushes Red Flag Warnings and Fire Weather Watches from the NWS the moment they're issued for your location, alongside every other severe weather alert type.
