Northern California Warms Up This Week, With Heat Advisory and Red Flag Warnings

“Thursday is our hottest day of the week,” said Karleisa Rogacheski, a lead meteorologist with the weather service’s Bay Area office. “We may have a couple of 100-degree spots sitting up in the North Bay and East Bay areas.”

The service has issued a red flag warning for the North Bay mountains and the East Bay Hills. The warning starts Wednesday at 11 a.m. and continues through Thursday morning due to gusty winds and critically dry conditions.

“This is a really strong setup for if a spark starts a fire, that fire is going to have the opportunity to grow very quickly in those areas,” said Brayden Murdock, a meteorologist with the weather service’s Bay Area office.

The service has also issued a heat advisory through Thursday evening for most of the region, extending from the North Bay to San Francisco to San José. Temperatures could reach near triple digits in inland areas like Santa Rosa and Livermore, while San Francisco and Oakland are expected to reach the low 80s by Thursday.

“Wednesday is going to be a pretty warm day and one of the warmest we’ve seen so far this year,” Murdock said.

Rogacheski said the warm-up isn’t considered a heat wave, but forecasters expect to reach the low 80s in San Francisco and the 90s and low 100s in the North, South and East Bay.

Rogacheski’s office is warning the public, especially in inland areas, that a moderate heat risk will begin Wednesday. That level of heat poses a risk of heat-related illness for sensitive populations, including children, the elderly and people who work or live outdoors.

“Pay attention to your body during these times because that’s kind of going to be an indicator of what might help,” Rogacheski said. “Take frequent breaks, rest in shade, stay hydrated and wear sunscreen.

The warm temperatures, winds up to 45 mph and decreasing relative humidity could create prime wildfire conditions if a spark were to ignite, Rogacheski said, for areas such as the eastern Napa Hills and the interior East Bay valleys and mountains.

“This isn’t a slam dunk red flag warning because all of our fuels aren’t fully cured and dried out,” Rogacheski said. “If there are locations that are dry, there could be easier fire starts and spreads, but there are areas that are still kind of green and moist. It’ll be a little bit harder for fires to start there.”

The weather service’s Sacramento office has issued a red flag warning for a large portion of the Sacramento Valley on Wednesday through Thursday evening, said Courtney Carpenter, the office’s warning coordination meteorologist.

“There could be a problem if anything gets started,” Carpenter said. “Fuels are drying out, and we’ve got gusty winds and low humidity, so that makes firefighting conditions challenging.”

In response, PG&E announced Monday that it may shut off power in parts of at least eight counties this week. The warning includes potential public safety power shutoffs through Friday in parts of Colusa, Glenn, Lake, Napa, Sonoma, Sutter, Tehama and Yolo counties. The utility shuts off power in order to limit the risk of wildfire from its equipment.

The company notes that only “some parts” of each county may be affected and that specific addresses are usually available two days before a shutoff occurs.