For San Luis Obispo County residents looking on with concern at the damage fires fueled by high winds are inflicting on Southern California — including the Ventura County Thomas Fire that has spread to 65,000 acres Wednesday — PG&E meteorologist John Lindsey wants you to remember one key thing.
The winds blowing down the mountains surrounding Ventura and the notorious “Santa Ana” winds of Los Angeles County have farther to go than similar winds coming over the Santa Lucia Range in San Luis Obispo County.
“They have more chance to accelerate down the canyons and passes,” Lindsey said.
He pointed to his Nov. 10, 2012 Tribune column to explain the significance of “downslope” winds like “Santa Anas,” which result whenever there is a large ridge of high pressure over the mountains. In Santa Barbara, they’re “sundowners.” They’re called “Diablo winds” in the Bay Area and “Chinooks” in the Pacific Northwest.
By any name, they are hot and dry.
“As the air mass descends the side of the mountain range, it warms at the rate of about 5.5 degrees Fahrenheit per 1,000 feet of descent,” Lindsey wrote in his column. “If the air is warm at the top of the mountain range, it can be sizzling hot and bone dry by the time it reaches the valleys below.”
The foothills of the Santa Lucia Range lack the elevation of their southern cousins — the Cuesta Grade rises to 1,522 feet above sea level, while the Santa Ana Mountains top out at the 5,689-foot Santiago Peak — so the winds don’t generate the same amount of heat, Lindsey said.
Another factor working in San Luis Obispo County’s favor is the comparatively greater amount of rain that falls here on average. That means vegetation in this county has a higher moisture content. Lindsey said that’s not the case for Ventura County.
“The fuel (vegetation) down there is at critical levels,” he said.
The mixture of dry wind and high daytime temperatures in Southern California is going to get worse before it gets better, Lindsey said.
The National Weather Service issued a wind advisory and red-flag warning for the Ventura area through 8 p.m. Friday, and fire danger will remain high, including in San Luis Obispo County, through Saturday. The NWS forecast for the San Luis Obispo area calls for sunny weather in the high 70s through Saturday, with a high of 80 on Sunday. Thursday will see east-southeast wind around 10 mph, and Friday will see east-northeast winds of 5 to 10 mph with gusts to 15 mph.
If there’s good news, it’s that long-range weather models show rain could return to Central and Southern California as early as Dec. 19-20. However, those models are prone to change.
“So take it with a grain of salt,” Lindsey said.