Dangerous heat wave begins in Bay Area; power shutoffs underway in fire-prone areas

A prolonged heat wave descended on the Bay Area and much of California Tuesday, with expected record-breaking temperatures creating dangerous conditions across the region, including in areas where power was shut off to prevent wildfires.

The National Weather Service said the heat wave will last through the 4th of July holiday, the weekend, and into next week. On Tuesday, the Weather Service extended an Excessive Heat Warning for the North Bay interior mountains and valleys, Sonoma and Marin coastal range, East Bay hills and interior valleys, Santa Clara Valley and eastern Santa Clara County hills until 11 p.m. July 9.

The extended warning also applied to the Santa Cruz Mountains, Santa Lucia Mountains, San Benito Mountains, and Southern Salinas Valley. The warning was also extended for a portion of California's Central Valley until 8 p.m. July 10.

Other parts of the Bay Area near the water are also under a Heat Advisory ; in San Francisco the advisory was extended until 7 p.m. Thursday, and through 11 p.m. July 9 for the Bay shoreline, the Northern Salinas Valley, Hollister Valley, Carmel Valley and Northern Monterey Bay.

In addition, the Weather Service extended its Red Flag Warning until 5 a.m. Friday because of critical fire weather conditions in the East Bay hills, Marin and Sonoma coastal ranges, and Santa Cruz Mountains. The Red Flag Warning extends through Wednesday evening for the northern part of the state and the Sacramento Valley. The Weather Service said the heat is combining with gusty offshore winds and very low humidity to increase the chance of fire starts in dry, open grasses.

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Tuesday morning, Pacific Gas and Electric said public safety power shutoffs were in effect for about 2,000 customers across small portions of eight counties - including Solano, Sonoma and Napa counties - and one tribal community. Another 10,000 customers have had their planned power outages delayed because of more favorable weather conditions, mostly in Glenn and Shasta counties, PG&E said.

The Weather Service said a high-pressure heat dome over the Bay Area will drive temperatures into the 90s by 11 a.m. and the 100s before 1 p.m. and it's expected some temperature records will fall on Tuesday. The low temperatures Tuesday evening and overnight in many inland areas will be well above average, remaining in the upper 60s or low 70s.

The heat dome is expected to linger over California for at least a week, and the long-range guidance suggests that timeline may be optimistic, the Weather Service said. Inland areas will have dangerous heat extending through the weekend at least, forecasters said.

"While we have all seen temperatures like this before, this event may end up approaching the upper end of what we've seen
historically, in terms of longevity," the Weather Service said in its daily forecast discussion Tuesday. "Heat is the #1 weather-
related killer in the United States. This is a significant heat wave, especially for inland areas. Please take the proper precautions, as impacts will only worsen day-by-day."

BART said its trains were running at slower speeds because of the hot weather to reduce the threat of derailments. When temperatures reach 100 degrees the tracks can slightly bend or distort.

Because of the possible high fire risk, the East Bay Regional Park District closed hills and inland parks Tuesday through Friday morning, subject to change, while shoreline parks and swim facilities remained open. In Concord, the city closed its open space areas, including Lime Ridge Open Space and trails within Newhall Community Park Tuesday through Wednesday evening at the recommendation of the Contra Costa County Fire Protection District.

People were urged to take measures to protect themselves and their loved ones during the prolonged extreme heat event. The risk of heat exhaustion and heat stroke is not just for those sensitive to heat but for everyone as the hot weather continues for days. A list of cooling centers can be found here .