What Is a Red Flag Warning?

A Red Flag Warning is a fire-weather alert. It tells you that the weather has turned dangerous for wildfire — not that a fire is burning, but that if one starts, it could spread fast and be very hard to stop. It is the fire-weather equivalent of a "take action" warning.

The conditions behind it

Red Flag Warnings are issued when several ingredients line up at once:

• Low relative humidity — dry air pulls moisture out of vegetation.
• Dry fuels — grass, brush and timber that are parched enough to ignite easily.
• Strong, gusty winds — which fan flames and carry embers to start new fires ahead of the main one.

Warm temperatures and occasionally dry lightning can add to the risk. Because what counts as "critical" depends on the local landscape, the exact thresholds are set by each NWS office together with fire and land-management agencies.

Watch vs Warning, fire-weather edition

• Fire Weather Watch — critical conditions are possible in the next 12–72 hours. Get ready.
• Red Flag Warning — those conditions are happening now or expected within about 24 hours. The danger is immediate.

It is the same prepare-then-act structure as every other alert — see watch vs warning vs advisory.

What to do (and not do)

• Avoid anything that throws sparks or flame — no open burning, campfires, fireworks, or grinding/mowing over dry grass during the heat of the day.
• Never discard anything burning — cigarettes and matches start a large share of human-caused fires.
• Don't park hot vehicles over dry grass — exhaust systems can ignite it.
• Be ready to leave — know your evacuation routes and keep a go-bag accessible if you live in a fire-prone area.
• Report smoke or fire immediately — minutes matter when winds are high.

Check your area

See whether a Red Flag Warning or Fire Weather Watch is active where you are with the free Weather Alerts tool. The same dry, windy setups often pair with an Extreme Heat Warning — and you can watch the wind and humidity driving the risk in the Weather Forecast tool.