Red Flag Warnings

Red Flag Warnings are issued by the National Weather Service when weather conditions are right for extreme wildfire events. These are days with sustained or gusty winds, and hot and dry conditions, that make wildfires more likely to ignite and spread rapidly. During these times extreme caution is urged by all residents. This is the time to stay on high alert, watch the news, and prepare for evacuation if needed.

Red Flag Warnings go out to the Marin community through Nixel, news outlets, and social media. Large signs with “Red Flag Warning” are also posted on major roads and intersections.

Red Flag Warnings are posted online on the California Fire Weather web page and on the web page for the San Francisco Bay Area National Weather Service (NWS) office.  Links to all fire weather forecasts and other NWS office web pages can be found on the National Fire Weather Page, including the forecast for the San Francisco Bay Area.

1. Don’t use barbecues or fire-pits outdoors.
2. Don’t use any source of heat or open flame outdoors, including, cooking, using power tools (gas or electric), or mowers.
3. Don’t smoke outdoors.
4. Avoid driving or parking in dry grass or vegetation.
5. Avoid closed areas and be alert while visiting (open) public lands where wildfires might occur.

Climate change is driving extreme weather conditions, making the fire seasons hotter, drier, and longer.  Since 1990, the average temperatures in California have risen 2° Fahrenheit; the fire season has increased by about 75 days; and, the acres burned have accelerated from 400,000 to over four million annually.

The Diablo Winds are strong wind events that flow northeasterly over Northern California’s coast in the fall when the moisture content is at its lowest.  These hot, dry winds can become quite strong with gusts reaching speeds of 40 miles per hour or higher, particularly along the ridges of the Coast Range. This effect is especially dangerous with respect to wildfires as it can enhance the updraft generated by the heat in such fires.

Fire danger ratings are measurements of weather and fuel conditions that help fire agencies predict how likely a fire may ignite, and how intensely and quickly it may burn.  These ratings are determined daily during fire season by local fire agencies based on the National Fire Danger Rating System (NFDRS).  These ratings are based on the probability of ignition; the effects of wind, slope, and fuel; and the potential energy released by a fire in the given weather and fuels.  A daily rating ranging from Low to Extreme level Fire Danger is determined based on the worst-case fire weather scenario during the hottest, driest part of the day on an open, south-facing slope.

Fire danger ratings may vary throughout the county and are used to determine whether land use restrictions will go into effect as well as how many firefighters should be available in case a wildfire does occur.  Fire Danger Ratings describe the potential for fire to ignite and spread rapidly in a local area.  Red Flag Warnings are a weather forecast used to predict a weather event in which fire will be difficult to control.