As California's fire season ramps up, San Jose State's Wildfire Interdisciplinary Research Center (WIRC) is fine tuning its next generation fire weather forecasting model on the state's largest active wildfires.
That model is the WRF-SFire model, one that has already shown the ability to simulate pyrocumulus development for the first time.
As wildfires exhibit pyrocumulus or lightning generating pyrocumulonimbus behavior, severe weather conditions can develop for fire crews on the ground and air. Besides lightning and briefly heavy rain at times, sudden strong wind shifts can send wildfires moving rapidly in different directions within minutes, threatening fire crews and communities near the fire lines.
The SFire weather modeling team is now running model runs on the state's larger wildfires this summer, including the Dixie Fire and Tamarack Fire. Both have shown extreme fire weather behavior at times.
Below: SJSU WIRC WRF-SFire model simulating changes in wildfire plume height.
So, what does extreme fire weather behavior look like?
Conditions on the Dixie Fire recently showcased these aspects as fire intensity increased rapidly during the afternoon hours, sending rising wildfire-heated air high into the atmosphere above the condensation level (area where temps cool to allow clouds to form) to at times reaching nearly 40,000-plus feet as captured on Alert Wildfire's network of cameras.
SJSU's Fire Weather Laboratory research has shown these intense vertical winds can match and exceed speeds seen in more traditional non-wildfire related severe thunderstorms and supercell thunderstorms.
Wildfires are known to create their own localized weather patterns, however, the more recent trend of much larger and more intense fires are correspondingly leading to more severe fire weather behavior as documented on the Carr Fire in 2018 when a large scale fire tornado occurred -- later rated to EF-3 in strength (winds up to 143 mph estimated by NWS Sacramento).
Being able to simulate and forecast for these potential extreme wildfire developments hours in advance is a critical tool that has remained out of reach mostly until the gains made more recently with the WRF-SFire model.
The need is certainly there with 85% of California's largest fires occurring since 2000, including five of the top six largest happening in 2020. This dramatic increase in wildfire growth and intensity continues to be driven by California's warming climate and more frequent drought.
This, combined with an overabundance of dead, overgrown forest fuels and fire suppression otherwise preventing natural fire processes from occurring, have upped the available fuel for wildfires once they develop in forest areas that haven't burned before.
The SJSU WRF-SFire model's ability to simulate with precision local smoke impacts and visibility for aircrews and extreme fire weather behavior looks to be in high demand this year with the 2021 fire season well ahead of the 2020 through mid-July in both events and acres burned.
Based on current conditions, it appears likely the team will have no shortage of wildfires to study to help improve their fire weather forecast model through the summer.