Santa Ana Conditions This Week for Southern California

Red Flag Warning Possible through Saturday

The National Weather Service has issued a Red Flag Warning for Southern California beginning in the early AM hours on Monday through (at least) Friday 1200 PDT. The areas will experience a significant Santa Ana conditions with the strongest winds expected Monday night and Thursday night into Friday. Offshore winds will exacerbate the problem by drying the air and reducing humidity to the single digits. This will likely be the strongest and longest Santa Ana event we have seen in the 2017 season.

Around this time two years ago we discussed what the thresholds are for a Red Flag Warning in Southern California. In this case, the National Weather Service sees the region’s relative humidity ≤15%, with sustained winds ≥ 25 mph and/or frequent gusts ≥ 35 mph (duration of 6 hours or more). The early event projections have even stated this could extend into next weekend. Specifically, wildfire danger will be most critical in the mountains and valleys of Los Angeles and Ventura counties. The combination of Santa Ana winds, low humidity, warm temperatures, and dry fuels will increase the risk for the rapid spread of any new fire starts. In response for this week, extra strike teams, and brush engines have been strategically staged in case of a big wildfire ignition.

RFW stats

This week’s expected Red Flag Warning statistics

Areas Impacted by Santa Ana Conditions:

Ventura County Mountains, Orange County, Los Padres National Forest, Los Angeles County Mountains, Angeles National Forest, Santa Clarita Valley, Cleveland National Forest, and San Diego County.

Click for official Santa Ana Conditions information: Red Flag Warning

santa ana conditions Dec 4

This week’s Red Flag Warning covers Southern CA from Santa Barbara to the border


Wildfire 101: Dead Fuel Moisture

What is Dead Fuel Moisture?

A recent lack of significant rainfall has kept Southern California in extreme drought, which means there is increased potential for significant wildfire due to dangerous levels of dead fuel moisture. As explained by NOAA, fuel moisture is a measure of the amount of water in a potential fuel, and is expressed as a percentage of the dry weight of that fuel.  So if leaves and downed trees were completely dry in a given area, the fuel moisture level would be 0%.

When fuel moisture content is high, fires do not ignite readily, or at all, because most of the fire’s heat energy is used up trying to evaporate and drive water from the plant in order for it to burn. When the fuel moisture content is low (like in drought-stricken Southern California), fires start more easily and can spread rapidly as all of the heat energy goes directly into the burning flame itself. When drought is extreme and the fuel moisture content is less than 30%, that fuel is considered to be dead, giving us the “dead fuel moisture” designation.

The United States Forest Service which manages a nationwide fuel moisture index, classifies fuel moisture based on two metrics:  fuel size and time lag.

  • Fuel size refers to the actual physical dimensions of the fuel (i.e. the diameter of downed logs or branches).
  • A fuel’s time lag classification is proportional to its diameter and is loosely defined as the time it would take for 2/3 of the dead fuel to respond to atmospheric moisture.  For example, if a fuel had a “1-hour” time lag, one could expect its wildfire susceptibility to change after only 1 hour of humid weather.  Fuels with 100- or 1000-hour time lags would be expected to be much less resistant to humidity.

Fuel moisture is dependent upon both environmental conditions (such as weather, local topography, and length of day) and vegetation characteristics.  The smallest fuels most often take the least time to respond to atmospheric moisture, whereas larger fuels lose or gain moisture slowly over time.

The classifications of the Forest Services’s index (also known as NFDRS) are as follows:

Dead Fuel Moisture

The Dead Fuel Moisture Time Lag Classes as defined by the United States Forest Service

Drought Conditions Improving in California

According to the weather almanac, San Diego–home to RedZone’s intelligence team–had received a minuscule .7 inches of rain since June 1st.  Luckily, a significant rain event entered the southern California region on Thursday evening, adding wetness to the low fuel moisture readings around the region.

Since late Thursday night (12/15), significant rains have finally fallen across the area. The gusty winds and showers are expected to begin tapering off late Friday as the moisture exits to the east, but a long-awaited significant wetting event has been left behind. Early reports on Friday (12/16) have measured up to 3.3 inches in the East County Mountains and greater than 1 inch along the San Diego Coast, far exceeding the cumulative totals since June.

As we discussed a few weeks ago, the drought situation in Northern California had already improved earlier this year, and now the dry weather in Southern California appears to be coming to an end.


Early November Fire Potential for SoCal, South

Every year, fire season comes to an end in the Western US as winter weather creeps in.  The northern high elevation forests soak in autumn rains and significantly lower temperatures, and the focus of fire potential subsequently shifts to only a few targeted areas.  Because of significant drought this season and persistent high winds, that focus remains on two regions in particular:  Southern California and the Southern Appalachian Mountains.

Another Offshore Event for Southern California

The seemingly year-round fire season in Southern California trudges on as fire services in the area remain at summer staffing levels.  Long term drought is constantly a factor in these areas, and periodic offshore wind events bring occasional elevation of wildfire concern. This week will mark the fourth such wind event of the fall with a Santa Ana event arriving today and lasting into Thursday, prompting a Red Flag Warning. Coastal areas from Santa Barbara through Tijuana will see significant fire potential as a result. The offshore event will particularly impact San Diego and Riverside Counties where the winds will be strongest and humidity lowest.

Southern California will see High to Severe Fire Potential on November 9th and 10th

Southern California will see High to Severe Fire Potential on November 9th and 10th

Elevated Fire Potential for Southern Appalachian Mountains

The 60 day percent of normal rainfall map (below) highlights significant rainfall deficits running from east Texas eastward to the western Carolinas. As a result, the Southern Appalachian area of the Southeastern US is in Preparedness Level 5 (PL 5) and has issued a ‘Fuels and Fire Behavior Advisory’ through November 20th. The advisory warns that the areas with highest rainfall deficits have very dry surface fuels that will support significant fires in high risk fuel types when elevated or critical fire weather is present.

Critically dry fuels and rampant fire ignitions have been observed from the Florida panhandle through Alabama to the mountains in Tennessee and North Carolina. Due to the concerning conditions, fire activity is peaking in the region. There are currently 38 ongoing, uncontained large fires in the region, many with incident command teams actively suppressing or patrolling them. By December, the area’s fire activity is expected to drop back to normal levels as temperatures cool to mostly seasonal ranges. In the meantime, two more weeks of concern lie ahead.

Rainfall deficits fueling major fire activity in the Southern Appalachian Mountains & prompting PL 5 in Southern Area

Rainfall deficits fueling major fire activity in the Southern Appalachian Mountains & prompting PL 5 in Southern Area



 NWS San Diego, CA

NIFC Predictive Services

Southern Fire Environment Outlook

SACC Morning Report