A forecast of strong winds coupled with high temperatures and low humidity has prompted the National Weather Service to issue a pair of Red Flag Warnings for critical fire potential this weekend across a wide swath of Northern California, including most of the Sacramento Valley and parts of the north Bay Area.
The NWS warning, issued Friday morning, will be in effect from 6 a.m. Saturday to 5 p.m. Sunday and supersedes the fire weather watch issued the day before.
The NWS Bay Area office’s Red Flag Warning will be in place for the North Bay Hills, in effect Friday evening through Sunday afternoon. NWS says the highest threat is anticipated near Eastern Napa County, in the Mt. Saint Helena region, due to “critically low humidity” and isolated gusts that could reach as high as 60 mph coming in from the northeast.
The highest potential for valley wind gusts will be Saturday in the western Sacramento Valley and northern San Joaquin Valley, forecasters said. Winds are expected to be from the north between 15 and 30 mph with gusts as high as 45 mph.
“Well above average temperatures combined with breezy to strong north winds will bring increased fire weather concerns this weekend,” the alert noted. “Daytime humidities will be low with poor humidity recoveries expected overnight Saturday. The wildland fuels are driest at the lower elevations, where there has been less precipitation over the last month. Therefore, the warning is in effect below the 1,000-foot level.”
Winds from the north will affect Sacramento and San Joaquin valley fire zones 215 through 219, which includes all of Sacramento, Yolo, Solano, Stanislaus and San Joaquin counties, as well as west-slope portions of foothill counties including Placer, El Dorado, Amador, Tuolumne, Sutter, Yuba, Colusa, Tehama and Butte.
Cal Fire spokesman Scott McLean said there’s a “very strong correlation” between large wildland fires and Red Flag Warnings, which serve as an important tool to heighten awareness and avoid complacency.
“There’s some times we have red flag warnings and (a wildfire) never happens. That’s really good, I like those days,” McLean said. “On the flip side of the coin, it’s a tool to warn the public and for us that monitor the weather ... Do we need to put staffing patterns on? Do we need to move some of our equipment from a non-Red Flag Warning area to this area?”
High temperatures in the forecast this weekend across most of the Sacramento Valley are expected to increase from the low 90s Saturday to high 90s Sunday, according to the latest NWS forecast.
Eastern Napa County will rise from the low 80s to upper 80s over the course of the weekend, forecasts show. Santa Rosa and Calistoga, which are largely surrounded by areas covered in the red flag warning but not included in the warning area itself as of Friday, will reach about 97 degrees Sunday.
Sacramento is expected to reach 90 degrees Saturday and hit 97 by Sunday.
Monday and Tuesday are currently expected to top out near 100 degrees in Sacramento. Redding’s forecast shows the Shasta County city hitting 106 by Tuesday.
McLean said it’s a particularly bad weekend for high fire risk, given that many high schools have outdoor graduation ceremonies planned, and that warm but relatively reasonable temperatures will promote a lot of other outdoor activity like camping or boating that can accidentally ignite a spark.
McLean urged the public to take great caution, noting that the state’s biggest fire, the Ranch Fire, “only took one spark to start.”