Red Flag Warning: the four-hour posture.

What a Red Flag Warning actually means

A Red Flag Warning is a forecast from the National Weather Service that within the next 24 hours, fire behavior is likely to be extreme if a fire starts. It combines three ingredients:

• Wind. Sustained 15+ mph or gusts 25+ mph. Wind is what turns a ground fire into a running crown fire.
• Low humidity. Below 15-25% depending on region.
• Dry fuels. Grass, brush, and timber below critical moisture thresholds.

None of these means a fire will start. All three means that if one does, it will move fast enough that evacuation windows are measured in minutes, not hours. Most catastrophic California and Colorado fires ignited during Red Flag Warnings.

The four-hour posture

When a Red Flag Warning is issued for your area, run this checklist. It should take under four hours the first time and under one hour after that.

1. Confirm you'll actually get the next alert

• Sign up for county emergency alerts if you haven't — in California, this includes Zonehaven and county opt-in systems.
• Enable Wireless Emergency Alerts on every household phone.
• Follow your local NWS office and CAL FIRE (or state equivalent) on social media for the fastest push updates.

2. Get the vehicle ready

• Fuel the primary vehicle to full.
• Load family go-bags into the trunk or by the door.
• Point the car nose-out in the driveway.
• Charge phones to full; leave a car charger in the vehicle.

3. Stage the house

• Close all windows. Move flammable patio furniture and doormats away from the house — this is a partial Zone 0 sweep.
• Bring in propane cylinders (grill tanks), or move them 30+ feet from the house.
• Turn off automatic sprinklers so they don't run dry when the power goes out.
• Coil garden hoses to reach any side of the house — for the fire department, not for you to fight fire.

4. Kill the ignition sources you control

• No outdoor burning, no burn barrels, no fireworks.
• No mowing dry grass — the mower blade striking a rock is a signature ignition source.
• No welding, grinding, chainsawing.
• No dragging trailer chains — a very common highway ignition.
• Park vehicles on gravel or paved surfaces, not in dry grass — hot exhaust ignites vegetation.
• Delay burning trash, fireworks, or any spark-producing task by 48 hours.

5. Prep for a PSPS (California)

In much of California, utilities preemptively cut power during Red Flag conditions — a Public Safety Power Shutoff. If you're in a PSPS zone:

• Charge phones, laptops, and battery banks to full.
• Fill jugs of drinking water.
• If anyone in the household has medical dependency on power, register with the utility's medical baseline program and pre-book a hotel or family stay on a different circuit.
• See our power outage preparedness guide for the full workflow.

6. Set the trigger to leave

Decide before it happens what makes you go. During a Red Flag Warning, drop your trigger points:

• Any evacuation warning for your zone: leave immediately.
• Visible smoke or the smell of smoke indoors: leave immediately.
• Any confirmed fire within 20 miles upwind: consider voluntary evacuation before an order is issued.
• Loss of cell service combined with smoke: leave.

What not to do

• Don't try to defend the house. US doctrine is evacuate; the fatality rate for civilians who stay is high.
• Don't rely on garden hoses in a wind-driven fire. Water pressure often drops or fails.
• Don't fill a pool as fire defense. It won't save the house and it puts you in the yard when embers are landing.
• Don't wait for the mandatory order. Voluntary evacuations avoid the traffic and keep roads open for engines coming in.

Related

• Wildfire evacuation checklist — the go-bag, the routes, the drill.
• Defensible space guide — the seasonal maintenance that pays off on Red Flag days.
• Wildfire smoke and air quality — because even a distant fire during Red Flag can pin you indoors for days.