Red Flag (Fire Weather) Warning
Definition:
A Red Flag Warning is issued when weather conditions create an extreme risk of wildfire. These conditions include:
- Very low humidity (less than 25%)
- Strong winds (sustained or gusts over 25 mph)
- Dry fuels (dead vegetation, grasses)
Criteria for Issuing a Red Flag Warning:
The National Weather Service (NWS) issues Red Flag Warnings based on the following criteria:
- 10-Hour Fuel Moisture: The average moisture content of vegetation in the top 10 inches of soil is below 5%.
- 1-Hour Fuel Moisture: The moisture content of fine fuels (such as grasses and leaves) is below 10%.
- Relative Humidity: The relative humidity is less than 25%, and there is a trend towards lower values.
- Wind Speed: Wind speeds are sustained at or above 25 mph, or gusts are expected to exceed 35 mph.
- Wind Direction: The wind is expected to be from the direction most favorable for wildfire spread.
Implications of a Red Flag Warning:
- Extreme wildfire risk: Wildfires can start easily and spread rapidly under Red Flag Warning conditions.
- Difficult firefighting conditions: High winds and low humidity make it challenging for firefighters to contain and extinguish wildfires.
- Public safety hazard: Wildfires can quickly threaten lives and property.
Recommended Actions:
- Monitor local weather forecasts and heed Red Flag Warnings.
- Avoid outdoor activities that could spark a wildfire, such as campfires, grilling, or smoking.
- Have an evacuation plan in place in case a wildfire occurs.
- Secure loose outdoor items that could be blown away by high winds.
- Be aware of road closures and other potential hazards.
Example:
On October 13, 2023, the NWS issued a Red Flag Warning for the Monadnock Region in New Hampshire. The warning was prompted by a combination of very low humidity, strong winds, and dry fuels. The Red Flag Warning advised residents to be prepared for increased fire danger and to take necessary precautions to prevent wildfires.
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