Montecito Debris Flow: A Historical Comparison to Southern California Debris Flows and an Analysis of the Forecast and Warning Challenges

The recently burned hills above Montecito due to the Thomas Fire presented a forecast challenge for meteorologists when a strong Pacific storm system moved through the area in the early morning hours of January 9, 2018. Very heavy rainfall fell in a short period of time over the Thomas burn scar just above the city of Montecito in Santa Barbara County. This torrential rainfall produced one of the more catastrophic post-fire debris-flow events on record in California, 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. This presentation will focus on the Montecito debris flow on January 9th and how it compared to historical debris flow events in Southern California, such as the post-fire debris flows from the Springs Fire burn scar near Camarillo on December 12, 2014, and the Station Fire burn scar near La Cañada-Flintridge on February 6, 2010. From a comparison of historical debris flow events, this presentation will also examine the forecast and warning challenges faced by National Weather Service Oxnard forecasters, less than a month after the hillsides above Montecito burned and the fire still actively burning at the time. An array of tools for interpreting data was used for storm interrogation, but this presentation will highlight the need for an expanded set of tools for future decision making, communicating the level of confidence in an historic event, and encouraging persons to take action to prevent the loss of life and property.