Northern California Starts to Sizzle Under Year's 1st Heat Wave

Updated 3:00 p.m. Tuesday

As the first heat wave of the year starts to bake Northern California, meteorologists expect Wednesday to be the hottest day of the week.

National Weather Service Bay Area meteorologist Dial Hoang said temperatures could soar up to 100 degrees midweek in parts of the North Bay, about 80 degrees in San Francisco and the upper 90s in San Jose.

Hoang said people in sensitive populations — children, the elderly, pregnant women, unhoused people and outdoor workers — should “take precautions” as the weather heats up.

“We’re advising people to take frequent breaks in the shade, stay hydrated, drink lots of water, and never leave children or pets in unattended vehicles,” he said.

Forecasters expect double-digit temperatures in inland areas like Contra Costa County and northern Napa County. The agency has issued a heat advisory for Tuesday through Thursday for interior parts of Napa, Sonoma, Contra Costa and Alameda counties. The weather service said it would likely expand the advisory on Wednesday to include Santa Clara, San Benito, and the far eastern portion of Monterey County.

Source: National Weather Service | Map by Matthew Green/KQED

As of 2 p.m. Tuesday, temperatures reached 91 degrees in parts of San Jose, 93 degrees in San Ramon and Concord, 96 degrees in Sonoma and 100 degrees in Suisun City.

“We will begin to slightly cool off Friday and into the weekend, but it’s still going to be warm,” said Nicole Sarment, a meteorologist at the NWS Bay Area office.

While people flock to the coast for a reprieve from the heat, Sarment warned of the possibility of sneaker waves and suggested inexperienced swimmers stay out of the ocean.

“We tell people to sit and watch the ocean for about 20 minutes before lying on the beach because these waves sneak up on the beach,” she said.

Meanwhile, the California snowpack could drastically dwindle as the heat wave increases temperatures to the upper 80s and low 90s across the Sierra this week.

“The heat wave probably won’t get rid of the snowpack completely, but it will get rid of a lot of it,” said Andrew Schwartz, lead scientist at the UC Berkeley Central Sierra Snow Lab.

The snowpack peaked in April, but it has already melted to a mere 44% of the normal level for this time of year. Due to the scarcity of snow in the Sierra, Schwartz said most snowmelt will occur at elevations above 10,000 feet, as lower elevations have “either completely or mostly melted out.” He doesn’t expect flooding from the snowmelt because of the lack of volume of snow remaining.

Still, the NWS advised people to exercise caution if they choose to cool off in rivers or streams this week because waterways will likely run fast and cold. State Climatologist Michael Anderson said reservoir operators will adjust their outflows since “many reservoirs are already near capacity thanks to the second year in a row of above-average snowpack.”

The heat wave, intensified by high humidity and strong winds, creates an immediate and potentially life-threatening environment due to fire risk in the state’s lower-elevation grasslands. The Bay Area saw a harrowing kickstart to its fire season over the past weekend as the Corral Fire touched off near Altamont Pass and, fueled by strong winds, quickly torched more than 15,000 acres of dry brush.

Meteorologist Sara Purdue from the NWS Sacramento office urged extreme caution, “Be aware of potential fire hazards, such as matches and cigarettes, and avoid parking your car on dry grass.”

At higher elevations, the likelihood of wildfires is still low, but Schwartz said the heat wave is “giving our forests and our fuels extra time to dry out ahead of fire season.”

Still, he said two wet years in a row means forests aren’t as dry as they were two years ago when drought permeated the entire state.