‘Marathon’ heat wave begins Tuesday in the Bay Area with triple-digit temperatures

After a gorgeously warm Sunday across the Bay Area, temperatures will start to creep up Monday, leading to a 10-degree jump by Tuesday morning that will leave much of the region baking on the Fourth of the July holiday and through the end of the week.

The National Weather Service has issued an “excessive-heat warning” for Tuesday morning through 11 p.m. Friday for much of the Bay Area, with the warning focused on hills and inland areas.

“It’s going to be hot for a really long time,” Weather Service meteorologist Nicole Sarment said. “The main thing is it’s not just going to be a one-day event. We are talking six, seven days of it.”

PG&E also has issued a notice that Public Safety Power Shutoffs are “likely” Tuesday in certain parts of Solano and Napa counties due to the heat, dry conditions and high winds. Other counties under watch for shutoffs include Glenn, Colusa and Lake. The Weather Service also has issued a fire weather watch for portions of northwestern Sacramento Valley and adjacent foothills between Tuesday morning and Tuesday evening, due to gusty winds and low humidity.

So far, the excessive heat forecast has not prompted the Bay Area Air Quality Management District to issue the Spare the Air Alert this week. However, air quality through Thursday is expected to be in the moderate range, between 50 and 100 on the Air Quality Index (AQI). This means that people who are unusually sensitive to air quality should consider limiting their time outdoors.

Temperatures in Concord, Brentwood, Livermore and Walnut Creek, respectively, are predicted to peak at 110, 108, 107 and 106 on Tuesday, with day-time highs expected to remain above 100 degrees in these cities, at least through the Fourth of July. Day-time temperatures in San Jose could reach 100 degrees this week, with Morgan Hill predicted to have highs of 102 on Tuesday and Wednesday.

With this extreme heat bringing potential fire danger, Weather Service meteorologist Rachel Kennedy also has said that officials are warning people to not use fireworks on the Fourth of July.

Cities along the coast and San Francisco Bay won’t get quite so hot and are under a “heat advisory,” rather than an “excessive heat warning.” Temperatures in Berkeley and Oakland should be in the relatively mild 80s this week, but San Mateo, Palo Alto and San Leandro should get hotter and see day-time highs in the 90s.

Areas directly along the coast should enjoy some relief from the heat, with temperatures in Half Moon Bay expected to reach the upper 70s this week. However, Santa Cruz could see temperatures jump to the mid-80s, starting Tuesday and on the Fourth of July. Kennedy said if there is any cooling marine layer along the coast this week, it should be “pretty shallow.”

For people in cities under the extreme-heat warning, the NWS has raised concerns about the “life-threatening impacts” of heat-related illnesses that can happen when people are exposed to multiple days of excessive heat.

In its forecast, the Weather Service said that people should consider this “prolonged heat event” as “a marathon, not a sprint,” when it comes to taking steps to minimize those impacts.

“This is not just for individuals sensitive to heat, but rather, the entire population,” the NWS said. “Heat for this duration and at these temperatures can be dangerous for everyone.”

What makes this heat wave especially intense is that people shouldn’t expect to get much relief from cooling overnight temperatures, Kennedy said. Starting Tuesday and Wednesday, the hills and inland areas may see temperatures remaining in the mid- to upper 70s overnight, she said. The impacts of the heat compound when it does not cool down overnight, leading to warming starting temperatures the next morning, Sarment also said.

When excessive-heat watches or warnings are in effect, the Weather Service advises people to suspend outdoor activities between 10 a.m. and 7 p.m. They should definitely pump up the air-conditioning if they have it. If they don’t have it, they should spend some time in an air-conditioned environments, such as stores, movie theaters, libraries, restaurants or cooling shelters.

The Weather Service also advises people to drink plenty of fluids and check in with vulnerable relatives and neighbors. Children and pets should not be left in cars unattended, as cars can reach lethal temperatures very quickly.

Kennedy said the hot weather is affecting much of California, with Death Valley already roasting on Sunday evening, with a temperature of 118 degrees. Often regarded as the hottest place on earth, Death Valley is expected to see temperatures as high as 122 degrees on Tuesday and 127 degrees on the Fourth of July. Death Valley’s record is said to be 134 degrees, recorded in 1913, though that record has been disputed. Temperatures of 130 degrees were recorded in the national park in 2020 and 2021.

The weather may start to cool on Saturday, though higher-than-normal temperatures are expected to continue through next weekend, Kennedy said. The Weather Service will revisit its forecast during the week to determine if it needs to extend the heat warning, she said.