Red Flag Warning vs Fire Weather Watch: What Each Alert Means
A Red Flag Warning means critical fire weather conditions are occurring now or will occur shortly. A Fire Weather Watch means those conditions are possible but not imminent, and the National Weather Service (NWS) issues it 18 to 96 hours before they are expected to begin. Both alerts come from local NWS offices working with fire and land management agencies, and the criteria that trigger them differ from region to region.
What is a Red Flag Warning?
The NWS issues a Red Flag Warning, in conjunction with land management agencies, to alert land managers to an ongoing or imminent critical fire weather pattern. Under NWS Instruction 10-401 (2025 edition), issuing one means forecasters have a high degree of confidence that weather and fuel conditions meeting local Red Flag criteria will occur in 48 hours or less. Forecasters can issue it for all or part of a fire weather zone.
The warning is valid from the time critical conditions are expected to start until the time they are expected to end. Its product header reads “URGENT – FIRE WEATHER MESSAGE.” On the NWS wildfire alerts page, the warning is labeled “Take Action,” with the advice “Be extremely careful with open flames.”
What is a Fire Weather Watch?
A Fire Weather Watch alerts land managers and the public that upcoming weather conditions could result in extensive wildland fire occurrence or extreme fire behavior. The NWS says a watch means critical fire weather conditions are possible but not imminent or occurring. Its label on the NWS page is “Be Prepared.”
NWS Instruction 10-401 says forecasters should issue a watch when there is a high potential for a Red Flag event, 18 to 96 hours before the expected onset. The intent is to alert users at least a day in advance for resource allocation and firefighter safety. The directive says a watch should not be issued, or continued, to indicate low confidence or borderline conditions.
| Alert | What it means (NWS) | Timing (NWS Instruction 10-401) | NWS label |
|---|---|---|---|
| Fire Weather Watch | Critical fire weather conditions are possible but not imminent or occurring | Issued 18 to 96 hours before expected onset | Be Prepared |
| Red Flag Warning | Critical fire weather is ongoing or expected to occur shortly | High confidence that criteria will be met in 48 hours or less | Take Action |
The pattern matches other NWS products, where a watch means a hazard is possible and a warning means it is happening or about to. Our guide to watch vs warning vs advisory explains how the NWS uses these words across hazards.
What conditions trigger a Red Flag Warning?
There is no single national threshold. NWS Instruction 10-401 says Red Flag criteria are set through coordination between each NWS forecast office and the land management agencies it serves, and documented in an interagency Annual Operating Plan. The criteria combine fuel dryness with weather.
The directive lists weather factors that can be part of the criteria: lightning episodes, a significant dry frontal passage, strong winds, very low relative humidity and dry thunderstorms. NWS fire weather program leaders also track fire danger indices and coordinate with land managers on how dry the fuels are.
Criteria published by four NWS offices show how much the numbers vary (as listed on each office’s website, November 2026):
| NWS office | Published Red Flag criteria |
|---|---|
| Grand Junction, Colorado | Relative humidity of 15% or less with sustained winds or frequent gusts of 25 mph or more, both for at least 3 hours in a 12-hour period; or widely scattered dry thunderstorms (15% or more coverage); fuels must be critical |
| St. Louis, Missouri | Sustained 20-foot winds above 15 mph, relative humidity below 25% and 10-hour dead fuel moisture below 9%, with all three exceeded |
| Jackson, Mississippi (for Mississippi) | Relative humidity of 25% or less and a 20-foot wind speed of 15 mph or more, among the criteria the office considers |
| Honolulu, Hawaii | Keetch-Byram Drought Index of 500 or more, relative humidity of 45% or less for 2 or more hours and sustained winds of 26 mph or more for 2 or more hours, mainly for leeward areas |
Grand Junction’s list is on its fire weather criteria page. To see the rules for your area, look for the fire weather page of your local NWS office.
Who decides, and how do fire agencies use these alerts?
Forecasters are expected to coordinate with local fire and land managers, and with Predictive Services at the National Interagency Fire Center or the regional coordination centers, before issuing a watch or warning. The final authority to issue a Red Flag Warning rests with the NWS.
The directive states the purpose plainly. These conditions alert land management agencies to the potential for widespread new ignitions or control problems with existing fires, both of which could threaten life and property. Local governments, emergency managers and fire officials receive the NWS information and provide the calls to action for the public.
In rare cases, when local criteria are greatly exceeded or near record levels, the NWS office describes the exceptional hazard in the warning’s headline and text. The product keeps the name Red Flag Warning. An office may also highlight particularly dangerous conditions for the public when that message is closely coordinated with emergency managers and fire managers.
Fire weather can last for days. The directive allows one watch or warning to cover a multi-day period with short breaks, and in that case the text explains when conditions are expected to ease.
How are SPC fire weather outlooks different?
The NOAA Storm Prediction Center (SPC) issues Fire Weather Outlooks, while local NWS offices issue the watches and warnings. SPC outlooks cover Day 1, Day 2 and Days 3–8.
SPC marks areas as Elevated, Critical or Extremely Critical for wind and relative humidity. It uses separate Elevated and Critical areas for dry thunderstorms. An outlook is a planning product for the days ahead, and it is not a Red Flag Warning.
Where can you see current Red Flag Warnings?
- Open weather.gov and enter your city or ZIP code. Active watches and warnings appear on the forecast page.
- Read the full alert text. It lists the affected fire weather zones and the valid time.
- See our active NWS alerts by state, such as current NWS alerts for California, which collect the official NWS messages in one place.
- For the days ahead, check the SPC Fire Weather Outlooks.
For local rules and actions during fire weather, follow your local fire agency and emergency officials.
Bottom line
A Fire Weather Watch says critical fire weather is possible within roughly the next one to four days. A Red Flag Warning says it is happening or expected within 48 hours, with high confidence. Each NWS office sets its own criteria with local fire agencies, so 15% humidity in Colorado and 45% in Hawaii can both mean a red flag. The NWS advice during a warning is to be extremely careful with open flames.
FAQ
Does a Red Flag Warning mean a fire is burning?
No. It is a weather alert about conditions that could support new fires or problems controlling existing ones. For active fires, see official incident updates; our guide to wildfire containment explains the terms they use.
How long does a Red Flag Warning last?
It lasts from the expected start of critical conditions to their expected end. The NWS can issue one warning for a multi-day event, with the text explaining any short breaks.
Why does Hawaii use 45% humidity when Colorado uses 15%?
Red Flag criteria are set locally between each NWS office and its fire agencies. The numbers reflect each area’s agreement, not a national scale.
Is a Red Flag Warning the same as a burn ban?
No. The NWS issues Red Flag Warnings about weather. Rules on outdoor burning come from fire and land management authorities, so check with your local fire agency.