Southern California’s Thomas Fire and the Deadly Montecito Debris Flow: NWS Successes and Challenges in Providing Impact-Based Decision Support Services for Preparedness, Response, and Recovery (Invited Presentation)

The Thomas Fire erupted on December 4, 2017 and burned 281,893 acres within Ventura and Santa Barbara Counties in southern California – becoming at the time what was California’s largest wildfire on record. The fire destroyed just over 1000 structures with 2 injured and 2 fatalities. The Los Angeles/Oxnard National Weather Service (NWS) office provided aggressive and timely Impact-Based Decision Support Services (IDSS) for NWS partners leading up to and during the strong Santa Ana wind event led to the fire. Partner response included nearly unprecedented pre-positioning and augmented staffing actions – employing staffing levels typically reserved for after a wildfire starts. NWS support continued during the fire by providing an Incident Meteorologist as well as conducting elevated IDSS prior to a strong "sundowner" wind event that threatened to spread the fire into populated areas of the Santa Barbara coast and brought about exceptional pre-positioning of fire agency resources. The threat of post-fire debris flows from the Thomas burn scar and other burn scars in the area began almost immediately given the fire's occurrence during southern California's rainy season. Numerous communities lie just beneath the Thomas burn scar, including the community of Montecito located along coastal Santa Barbara County. Anticipating the impacts from a strong Pacific storm system forecast to move through the area in early morning hours of January 9th, the Los Angeles/Oxnard NWS office began providing aggressive IDSS as much as six days in advance of the storm. This included very active web postings and social media messaging along with special calls, email briefings, and webinars for critical partners preparing for the storm. Partner actions included activating the Santa Barbara County Incident Command Post (ICP) and issuing evacuation orders just over of a day prior to when the storm was expected to arrive. The storm ultimately produced exceptionally heavy rainfall of up to six tenths of an inch in just five minutes over the Thomas burn scar just above Montecito. This torrential rainfall tragically produced one of the more catastrophic debris-flow events on California record, resulting in 21 fatalities and 2 residents still missing and presumed deceased, a total of 128 single family residences destroyed and 307 damaged, and 6 commercial properties destroyed and 17 damaged. U.S. Highway 101 - a major route for commuters between Ventura and Santa Barbara - was closed for 12 days due to extensive flooding and debris. Although so many lives were lost, emergency response agencies – who had additional and pre-positioned resources in place in part from the active IDSS that was provided – were able to conduct 1000 rescues in the first 24 hours. Officials estimate the number of fatalities could have been doubled had it not been for these resources in place for immediate response. Local NWS IDSS continued after the debris flow to support rescue, recovery, and debris removal – most notably in providing weather briefings on over 100 joint agency conference calls and providing daily spot forecasts. The threat of post-fire debris flows continued well into March, with several additional storms impacting the area and culminating in the NWS Los Angeles/Oxnard office providing onsite support at the Santa Barbara County ICP March 21-22. This onsite support was a major contributor to the decision to lift evacuation orders on March 22 – more than twelve hours earlier than planned. In addition to an overview of successes and challenges associated with forecasting and warning for these two extreme events, this presentation will describe the aggressive IDSS provided to partners and highlight their resulting preparedness actions intended to mitigate property damage and loss of life. Also covered will be the challenges and lessons learned of communicating debris-flow threats to the public in a way that helps ensure this rare but deadly natural hazard is understood, and protective action is taken in a timely manner. Results of a post-event public survey intended to better understand the public's response to this debris-flow threat and instructions from local officials are presented to reinforce these challenges.