Abstract

The November 2018 Camp Fire quickly became the deadliest and most destructive wildfire in California history. In this case study, we investigate the contribution of meteorological conditions and, in particular, a downslope windstorm that occurred during the 2018 Camp Fire. Dry seasonal conditions prior to ignition led to 100-h fuel moisture contents in the region to reach record low levels. Meteorological observations were primarily made from a number of remote automatic weather stations and a mobile scanning Doppler lidar deployed to the fire on 8 November 2018. Additionally, gridded operational forecast models and high-resolution meteorological simulations were synthesized in the analysis to provide context for the meteorological observations and structure of the downslope windstorm. Results show that this event was associated with mid-level anti-cyclonic Rossby wave breaking likely caused by cold air advection aloft. An inverted surface trough over central California created a pressure gradient which likely enhanced the downslope winds. Sustained surface winds between 3–6 m s−1 were observed with gusts of over 25 m s−1 while winds above the surface were associated with an intermittent low-level jet. The meteorological conditions of the event were well forecasted, and the severity of the fire was not surprising given the fire danger potential for that day. However, use of surface networks alone do not provide adequate observations for understanding downslope windstorm events and their impact on fire spread. Fire management operations may benefit from the use of operational wind profilers to better understand the evolution of downslope windstorms and other fire weather phenomena that are poorly understood and observed.

Highlights

  • Introduction and BackgroundMany of California’s largest, deadliest, and destructive wildfires occur during strong downslope windstorms

  • Live and dead fuels typically reach their minimum in fuel moisture content (FMC) in the fall, September–October, due to the lack of precipitation, high temperatures, and low relative humidity (RH) experienced throughout the summer

  • The only precipitation occurred between 3–5 October, when the FM-100 at all remote automated weather station (RAWS) reached a relative maximum and declined through 25 October (Figure 3)

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Summary

Introduction and Background

Many of California’s largest, deadliest, and destructive wildfires occur during strong downslope windstorms. DW typically refer to the foehn winds that occur in the San Francisco Bay Area (SFBA) region, notable occurrences include the Wine Country/Napa county fires of 2017, the Tubbs Fire, and the Tunnel Fire in the Oakland Hills in 1991 [15,16,17]. These winds are similar to SAW, with hot, dry, gusty downslope winds that predominantly occur in the fall [16,17]. The structure of this paper is as follows: Section 2 describes the data and methods used in this analysis, Section 3 details the observed and modeled conditions prior to ignition as well as the conditions associated with the downslope windstorm event, Section 4 presents model verification metrics, and Section 5 summarizes the results and presents further discussion

Observations
Modeled Data
Precipitation and Fuels
Synoptic Overview
National
Calculated in the the area area surrounding surrounding the the Camp
WRF Analysis
November are plotted with the nearest
Model Verification
Discussion and Conclusions
November created more allowing wildfire
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