Bobcat Fire, Southern California

Wildfires are becoming a common occurrence in southern California. Limited amount of precipitation from the monsoon season combined with the extreme hot temperatures allowed the hills above Los Angeles to dry out. The fire that began on September 6th would continue to grow, becoming the largest fire within Los Angeles County history.

Leading up to the start of the Bobcat Fire, environmental conditions were primed for significant fire activity. In the days before the start of the fire, a significant heat wave impacted the area with high temperatures between 100 and 110 degrees. The high temperatures, along with relative humidity in the 5 to 15 percent range, continued to dry out the vegetation. In fact, Live Fuel Moisture levels, which measure the amount of moisture in live vegetation, were ranging between 55 and 70 percent. In Southern California, the critical level for Live Fuel Moisture is 60 percent.

While there may not have been a fire weather watch or red flag warning for the upcoming weekend, NWS Los Angeles began messaging the concern for large fire activity.

• September 6: Fire Reported
• September 8: 8,553 acres (Morning Estimate)
• September 9: 11,456 acres (Morning Estimate)
• September 10: 23,890 acres (Evening Estimate)
• September 11: 26,368 acres (Morning Estimate)
• September 12: 29,245 acres (Morning Estimate)
• September 13: 31,991 acres (Morning Estimate)
• September 14: 36,336 acres (Morning Estimate)
• September 15: 41,231 acres (Morning Estimate)
• September 16: 44,393 acres (Morning Estimate)
• September 17: 50,539 acres (Morning Estimate)
• September 18: 60,557 acres (Morning Estimate)
• The fire continued to grow for the next few months
• December 18: 115,796 acres (100% Contained)

Extremely hot temperatures, humidities down into the single digits and strong gusts were going to impact southern California. Resources were always stretched thin so getting ahead of critical fire weather days could help relieve the stress of trying to find additional firefighters.

• September 4th and 5th at 1:00 PM PDT: WFO LOX initiated Fire Weather Conference calls with our local fire partners. LOX forecasters were able to relay the latest forecast details as well as receive vital fire intelligence such as fuel conditions and potential fire behavior.
• September 4th at 2:40 PM PDT: Fire Weather Watch issued for Fire Weather Zone 254. Winds 15 to 30 mph with gusts to 45 mph and relative humidity as low as 7%. Very hot temperatures up to 107º.
• September 5th at 10:05 AM PDT: Red Flag Warning issued for Fire Weather Zone 254. Winds 15 to 30 mph with gusts to 45 mph and relative humidity as low as 7%. Very hot temperatures up to 110º.

Winds began to pick up while temperatures began to reach scorching temperatures on September 6th. Camera's that were pointed at the hills surrounding Los Angeles and were able to capture the start of the Bobcat Fire. While the cause is still unknown, it is thought that the fire began by power line conductor torching overhead trees. As of mid March 2021, this is yet to be confirmed.

With the strong winds, this fire was able to move quickly.  Alert Wildfire  has cameras positioned all across California and it happened that the Mt. Wilson Camera was pointed in the direction of the fire and caught the initial spread.

Let's look at pyrocumulus clouds for a minute. NASA wrote a blog going into depth explaining what they are and how they occur.

Pyrocumulus clouds—sometimes called “fire clouds”—are tall, cauliflower-shaped, and appear as opaque white patches hovering over darker smoke in satellite imagery. Pyrocumulus clouds are similar to cumulus clouds, but the heat that forces the air to rise (which leads to cooling and condensation of water vapor) comes from fire instead of sun-warmed ground. Under certain circumstances, pyrocumulus clouds can produce full-fledged thunderstorms, making them pyrocumulonimbus clouds." - NASA

For more information, you can view the rest of the blog  here .

Conditions continued to look bleak for any relief for the Bobcat fire as the afternoon turned into evening.

Large chunks of ash were visible across Los Angeles on the morning of September 7th. This tweet shows a chunk of ash up to a half inch in size.

Even 40 miles away, it was raining ash.

The fire was contained on December 18 but not before is 28 residences were damaged and another 27 destroyed. It also damaged 19 other structures and destroyed 83. Six firefighters were injured from this fire and an estimated $80 million in damages were done.

The Bobcat fire became one of the largest fires recorded in the Los Angeles area. During this same time, the El Dorado Fire continued to grow to near 27,000 acres. Air pollution continued to be a concern for several months in Los Angeles.

Incident Meteorologist (IMETs) are NWS meteorologists who embed with the Incident Management Teams coordinating the firefighting effort. Their 24/7 presence at the Incident Command Post and in the field along with the firefighters builds trust which ensures the IMETs weather input will play a key role in critical decisions. On the Bobcat Fire, Richard Thompson (from NWS LOX) was the IMET assigned.

Most people associate large and impactful Southern California fires with Santa Ana wind events. The Bobcat Fire, much like the Station Fire in 2009, was an example of a significant fire in the absence of Santa Ana winds. The hot and dry conditions, combined with typical Summertime terrain-driven winds, allowed for a majority of the fire growth, including the fire spread into the Antelope Valley foothills on September 17-18. -IMET Rich Thompson