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Home , Santa Ana winds, San Diego

Developing and Validating the Santa Ana Threat Index

Tom Rolinski1, Robert Fovell2, Scott B Capps3, Yang Cao2, Brian D”Agostino4, Steve Vanderburg4 (1)USDA Forest Service (Predictive Services), Riverside, CA, , (2)Department of Oceanic and Atmospheric Sciences UCLA, , CA, United States, (3)Vertum Partners, Los Angeles, CA, United States, (4)SDG&E, , CA, United States

65 60 LFP depicting Santa Ana Events 2007-2014 55 Santa Ana Events – weather parameters only 50 Santa Ana Events – weather and fuels 45 40

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LFP 30 25 20 15 10 5 0

1- Introduction 2- Methodology From the fall through spring, offshore , commonly referred • The SAWTI which predicts Large Fire Potential (LFP) during to as "Santa Ana" winds, occur across southern from Santa Ana wind events, is informed by both weather and fuels Used by fire agencies and the general public, the Santa Ana Wildfire Threat Index (SAWTI) was made publically available on September 17, 2014. The product Ventura County south to and west of the coastal information. can be accessed at: santaanawildfirethreat.com mountains and passes. Each of these synoptically driven wind • We define LFP to be the likelihood of an ignition reaching or events vary in frequency, intensity, duration, and spatial coverage, exceeding 250 acres or approximately 100 ha. thus making them difficult to categorize. Since fuel conditions • For SAWTI, the following equation was formulated: 4- Operational SAWTI tend to be driest from late September through the middle of In 2013, the SAWTI was beta tested through a controlled 2 November, occurring during this time have the 퐿퐹푃 = 푊푠 퐷푑퐹푀퐶 release via a password protected website. On September greatest potential to produce large, devastating fires when an 17, 2014, the USDA Forest Service conducted a press ignition occurs. Such catastrophic fires occurred in 2003, 2007, Where Ws is the near surface wind speed, Dd is the near surface conference at which time the product was made publically 2008, and 2014. Because of the destructive nature of such fires, dew point depression, and FMC is the Fuel Moisture Component available. Since then it has been featured on numerous there has been a growing desire to categorize Santa Ana wind expressed by this equation: The SAWTI shown on (TWC) on the day of the news stations and on The Weather events in much the same way that tropical cyclones and press conference (September 17, 2014). Channel. When discussing upcoming Santa Ana wind 1.7 tornadoes have been categorized. 퐷퐿 events, The Weather Channel uses the SAWTI output. 퐹푀퐶 = − 1 + 퐺 퐿퐹푀

Where DL is a Dryness Level index (a function of the Energy 5- APPLICATION Release Component [ERC] and Dead Fuel Moisture [DFM]). LFM is SAWTI in beta test mode provided operational guidance the Live Fuel Moisture of Chamise (Adenostoma fasciculatum), and during 13-14 May 2014 G is the green-up/curing of the annual grasses using the • Extreme weather and fuel conditions (map below left) Normalized Difference Vegetation Index (NDVI). KUSI news in San Diego showing a Google search provides a list of were forecasted for this event up to 5 days in advance direct link to the product on their news articles on the release of • Multiple fires occurred over San Diego County on 13-14 Major passes in southern California that favor High resolution satellite image showing the fires main web page. the SAWTI Santa Ana winds. Zones were used in beta that occurred across southern California in 2003 May 2014 test product. During the past three and a half years, the Forest Service (through 3- Fuels The authors acknowledge: Dr. Robert Fovell and Dr. Yang Cao, Predictive Services) has collaborated with the San Diego Gas and Fuel moisture plays a critical role in the UCLA Brian D'Agostino and Steve Electric utility (SDG&E) and the at Los propagation of . FMC incorporates Vanderburg, San Diego Gas and Angeles (UCLA) to develop the Santa Ana Wildfire Threat Index 3 kinds of fuel moisture (DFM, LFM, and G) Electric

(SAWTI), which categorizes Santa Ana wind events according to because each component can be in phase For more information, please the potential for a large fire to occur. This unique approach or out of phase with each other. contact : Dr. Scott B. Capps at addresses the main impact Santa Ana winds could have on the Considering any one [email protected] Tom Rolinski at [email protected] population of southern California beyond experiencing the casual component alone may Map depicts effects of windy, dry weather. active fires give a false (icons) on May representation of fuel Map above depicts fire potential during the May 14, 2014 Santa Ana 14, 2014 across event. Colors represent the product of wind speed squared (mph) and San Diego moisture. the dew point depression (˚F) County.