Heat Wave in Northern California Brings Dangerous Temps, High Fire Risk

With Fourth of July celebrations just around the corner, weather forecasters are warning Bay Area residents to remain vigilant in light of the extreme heat conditions and increased fire risk expected this week.

Even in the city of San Francisco, which is generally shielded from the high temperatures by cool coastal air, a heat advisory will be in effect from 11 a.m. Tuesday through 7 p.m. Wednesday. Highs in the mid-80s are expected, though there’s a chance for 90-degree heat in the southern and eastern parts of the city, according to the latest forecast discussion from the National Weather Service.

In the East Bay, warmer conditions and prolonged heat mean the advisory is set to last even longer, from Tuesday morning through Saturday evening. Across the North Bay and areas farther inland, an excessive heat warning will be in effect, with temperatures ranging from the upper 90s to 110.

Lamont Bain, a meteorologist with the National Weather Service, noted that the upcoming holiday falls directly within the heat wave, reminding residents to remain conscientious and to limit their prolonged exposure to the heat.

“We just want people to be smart, be hydrated and take frequent breaks,” Bain said. “Don’t be out in the sun too much, and know the signs of heat stroke: dizziness, fatigue and other signs of dehydration.”

In addition to the daytime heat, elevated overnight temperatures and low humidity levels in the North Bay and in the East Bay hills will pose a huge fire risk.

A red flag warning in the East Bay will be in effect from Monday evening through Tuesday evening. According to Bain, a similar alert in the North Bay will run for even longer until Wednesday evening.

“Typically, the humidity recovers really, really high during the overnight hours,” Bain said. “However, because it’s going to be warmer, those relative humidity levels during the overnight hours are going to remain dry or low. And that essentially results in the potential burn period.”

Firefighters have already had to contend with multiple grass fires in recent days amid the persisting dry conditions. In eastern Fresno County, the Basin Fire has burned over 12,600 acres with 0% containment since it started on Wednesday, forcing evacuations.

With the elevated fire risk this week, PG&E said Sunday that it could shut off power in parts of Northern California due to high winds and heat to avoid sparking a wildfire. As of now, however, nothing has been announced.

The heat wave has also spurred concerns over air quality. Due to the high inland temperatures, weak sea breeze and concentrated motor vehicle exhaust, the Bay Area Air Quality Management District issued a Spare the Air alert for Tuesday, warning that the resulting smog may reach unhealthy levels.