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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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RedZone Disaster Intelligence

October Brings Highest Risk of Destruction to California

This past weekend, from Saturday into Monday morning, much of the Northern California Bay Area was under a Red Flag Warning due to strong winds around 40 mph with gusts to 60 mph. Despite much of the country receiving some level of precipitation recently, California remains just above the drought threshold. The gusty winds and dry fuels the state sees every fall leads to heightened fire weather conditions this time of year. Fortunately, with this strongest wind event thus far this Fall, fire agencies across the region responded rapidly and en masse to any new reports of ignition.

“Of the twenty most destructive wildfires in CA history, eleven of them have happened in October and another three in November or December.”

Transitioning out of Western Fire Season

Most of the Western fire season began the seasonal transition out of its peak in early September with fall’s cooler temperatures and precipitation. October and November mark another transition as the focus typically shifts to California  where fire activity remains a major concern with summer-dried fuels and occasional Foehn wind events develop across California until winter rains come.

October Fire potential

Significant Wildland Fire Potential for October 2018

Brief Look Back to October 2017

Monday, October 8th, marked one year since 21 major wildfires started across Northern California and devastated the Napa-Sonoma area. Collectively the fires burned more than 245,000 acres over the course of the month. The Northern California Firestorm, as it came to be called, destroyed nearly 9,000 structures and was responsible for 44 civilian fatalities and caused 14.5 billion dollars in damages.

The fire spread was remarkable as ember showers spread from house to house throughout several communities and the fires moved at record-setting speeds. Gusting and strong winds were an instrumental driving force behind the massive levels of damage caused by the conflagrations. What wasn’t record setting was this type of fire weather happening in October or later in California. As the table below shows, of the twenty most destructive wildfires in CA history, eleven of them have happened in October and another three in November or December.

14 top fires have happened in October and later

14 of the Top 20 Most Destructive California Wildfires have started in October or later

Obviously all that late season activity means, historically, the Western Fire Season is far from over in California. Fire Departments remain at full staffing, on the ready, with ears perked to every new start that could be the next big one…especially with the fire weather possibilities this time of year. RedZone does the same, and those of you in the insurance world reading this, so too should you. Those 14 wildfires have collectively caused tens of billions of dollars in damage over the years.

Read Further

http://www.latimes.com/local/lanow/la-me-ln-santa-ana-winds-20180925-story.html

https://www.wrh.noaa.gov/fire2/?wfo=mtr

https://www.kron4.com/news/bay-area/red-flag-warning-this-weekend-in-parts-of-bay-area/1502972515

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.