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Autumn and Santa Ana Winds

Fall Means Santa Ana Winds

Annually, the onset of the fall and winter seasons brings the highest chance for Southern California’s famed Santa Ana winds. Historically, the worst fires in Southern California in terms of speed of growth and destruction are linked to these hot, dry wind events. The last two years, a strong and persistent Santa Ana event was a major player in the spread of both 2017’s Thomas fire in Ventura and Santa Barbara and last year’s Woolsey Fire in Malibu. 

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Autumn and Santa Ana Winds

Fall Means Santa Ana Winds

Annually, the onset of the fall and winter seasons brings the highest chance for Southern California’s famed Santa Ana winds. An unusually strong and persistent Santa Ana event was the largest factor in the spread of last year’s Thomas fire in Ventura (now second largest in size to Mendicino Complex). Much of Southern California experienced an on-and-off Santa Ana wind event for a little over two weeks, which contributed to the Thomas Fire burning a hot lap around Ojai and into Santa Barbara.

What Are Santa Ana Winds?

Typically Santa Ana air mass conditions are brought on by high pressure inland and lower pressure off the Pacific Coast which brings very hot and dry weather along with strong, down-slope winds.  Santa Ana winds typically happen between September and May, in the winter months. We think this UCLA FAQ outlines Santa Anas the best. In the past, the critical fire weather conditions that accompany Santa Ana winds turn the typically dry chaparral of Southern California into explosive fuel.  Some of the country’s costliest fires in history have taken place in these conditions.

Santa Ana Winds

Santa Ana Winds derive from High Pressure in the Great Basin

The Outlook This Fall

Typically, a weather event occurs by mid-September that brings moisture to regions experiencing significant fire activity which allows for the western fire season to begin to decrease in activity. All signs point to a normal seasonal progression including a transition from ENSO Neutral conditions to El Niño, therefore such an event is expected. Most regions will exit the fire season at this point, but only a brief lull is expected across California before it enters its fall fire season by October and November. Given ongoing dryness in the fuels, the fall season may very well be robust across portions of the state. Fortunately for the drought situation, Meteorologists are expecting an El Niño cycle to begin affecting the area with rains by November.  In the meantime, as the tropical air mass that has brought this summer’s rain gives way to autumn’s Pacific air mass, a few Santa Ana events should precede the El Nino’s wetting effect. 

 

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


 

Sources:

 NWS San Diego, CA

NIFC Predictive Services

Southern Fire Environment Outlook

SACC Morning Report