Red flag warnings were issued for much of interior Northern California starting Thursday night due to strong winds and dry conditions that could lead to fire danger.
The National Weather Service issued a warning Tuesday morning, overcoming fire weather warnings issued the day before, as winds known as Diablo winds are expected to begin blowing from the north as a small weather system moves across the region. Updated warning.
Meteorologists said the fast-moving storm, which is expected to bring brief periods of light rain on Wednesday, would open the door to “significant fire weather conditions” through Saturday.
“The biggest concern with this main part of the system remains its path into the Great Basin,” the National Weather Service’s Sacramento office said in a forecast discussion Tuesday. “This is a typical fall ‘inside slider’ pattern, with north to east winds and low relative humidity during the day into the weekend.”
Diablo’s wind is expected to blow
Diablo winds, known as Santa Ana winds in southern states, are a fall season that carry warm air from Nevada and Utah into California, drying grass and creating conditions that can cause fires to spread quickly. The lack of onshore wind from the Bay Area only creates extreme conditions.
This situation was most evident in 2017, when high pressure pushed dry winds into the state from the Great Basin, fueling the Santa Ana winds that fueled the devastating Wine Country fires and firestorms in Southern California.
The latest red flag warning will go into effect for much of the Sacramento Valley and foothills and the upper San Joaquin Valley starting Thursday at 11 p.m., forecasters warned.
May be windy and low humidity
Gusts at the valley floor could reach 45 mph with sustained winds of 15 to 25 mph. However, the windiest areas are expected to be in the Sacramento-San Joaquin Delta, with wind speeds of 20 to 30 mph and gusts up to 55 mph.
The situation on the ground will not be much better. Forecasters said there would be little moisture recovery with overnight conditions expected to be “moderate to poor” with humidity ranging from 10% to 25% on Friday and Saturday.
“The combination of high winds and low humidity could cause new fires to start and rapidly increase the size and intensity of ongoing wildfires,” the warning said.
Temperatures in the region will be at or near normal, with highs in the lower to mid 80s in the valley and 60s to 70s in the foothills, forecasters said.
Long-term forecasts also suggest that a cooling trend from onshore winds that will re-emerge on Sunday will lead to more favorable conditions next week.
Which counties are covered?
This warning covers the following areas:
Amador below 1,000 feet
Butte County (includes hills above 1,000 feet elevation)
colusa county
El Dorado County Below 1,000 feet
glen county
Placer County below 1,000 feet elevation
sacramento county
San Joaquin County
Shasta County, north of Redding via Lake Shasta
Solano County
Stanislaus County
Sutter County
Tehama County (includes hills above 1,000 feet elevation)
Yolo County
Yumiba District
Warnings for fire zones 213, 215, 216, 217, 218, 219 and 266 will remain in place until 5 p.m. Saturday, but the strongest winds are expected on Friday, forecasters said.
