Cal Fire ready for its highest-risk time of the year

As many fire crews across North America are ending their official wildfire seasons, Cal Fire is now gearing up for its most at-risk time of the year.

Seven of California’s top 20 most destructive wildfires (“most destructive” meaning fires that resulted in the most structures destroyed or lives lost), over the years have occurred in the month of October. The top three on the list after the November 2018 Camp Fire, all burned in October, including the 2017 Tubbs Fire, the 1991 Oakland Hills firestorm (with the Tunnel Fire), and the 2003 Cedar Fire.

Plus of course the October 2006 Esperanza Fire.

On the morning of October 20, 1991, towering clouds of black smoke blocked out the sun as “diablo winds” whipped flames hot enough to melt gold throughout the hills above Oakland and Berkeley.
On the morning of October 20, 1991, fearsome Diablo winds whipped flames hot enough to melt gold across the hills above Oakland and Berkeley.

Cooling temperatures and incoming moisture often provide relief to much of the country during early autumn, but conditions in especially dry parts of California can blow up wildfire risk in the state thanks to a combination of summer’s dry vegetation and fall’s fierce winds.

“It is a common misconception that the most dangerous time for fires in California is during July and August,” according to the Western Fire Chiefs Association website. “While there may be fewer fires in September and October, the fires that do occur are far more destructive and burn through many more acres.”

October 2006, en route to the Esperanza, photo by Laguna IHC.
October 2006, en route to the Esperanza Fire, photo by Laguna IHC.

This explosive wildfire situation is caused mainly by a combination of dry vegetation from hot summer weather and the intense dry winds that blow over California fires in the fall.

Known as the Santa Ana winds in southern California and the Diablo winds in northern California, they’re characterized by downslope gusts blowing from the mountains toward the coast. Despite their different names, the winds are caused by similar autumn weather patterns, differing mostly by their locations — the Santa Anas in the south blow down from the Santa Ana Mountains, while the Diablos  in northern California blow from the Diablo Range. 

Oakland Hills 1991
1991 Oakland Hills firestorm. View of the fires above the Claremont Hotel on October 20, 1991. Oakland local wiki pages.

And while these autumn winds now build in the state, some areas are still benefiting from the record-breaking wet winter across the Southwest at the beginning of 2023. Crews in the Santa Cruz area reportedly had to start their season late since the ground was too wet to conduct planned prescribed burns.

“Because it was so moist, my burn crews were not available until early July,” Sarah Collamer, forester and Cal Fire burn boss, told KSBW. “We usually burn in June, but it was too wet.”

As we head into October, we’ll see who wins in the perennial battle between seasonal dry winds and the unseasonal wet ground.