Heat waves and cooling centers

Most summer days in Palo Alto top out in the upper 70s and the bay keeps nights cool. Then a ridge of high pressure parks over California, the sea breeze fails and the city bakes. The all-time record of 108°F came on September 6, 2022. In early October 2026 the National Weather Service issued a heat advisory for the Bay Area through October 8, with the city warning of highs from the upper 80s to the low 100s.

Heat is easy to underestimate here because so many homes, especially older ones, were built without air conditioning. A house that stays comfortable all summer can turn into an oven on the third day of a heat wave. This guide gathers what the city, the county and Ready.gov advise. For month-by-month temperatures, see our weather guide.

When heat waves happen

Locals know that September is often the real summer. It is the warmest month on average and heat waves can run from June into October. The foothills along Page Mill and Arastradero roads usually run hotter than the flat neighborhoods near the bay. Heat also tends to arrive with other problems: higher fire danger in the hills, worse air quality and strain on the electric grid.

Ready.gov defines extreme heat as temperatures above 90°F for at least two to three days, with humidity making it feel worse. That multi-day pattern is the risk. One hot afternoon is uncomfortable. Three hot nights in a row without cooling is when people get sick.

How you will hear about it

The National Weather Service Bay Area office issues heat advisories and warnings. The city reposts them as news alerts that list cooling centers and safety tips. Sign up for the city's news emails or follow its social accounts and keep Wireless Emergency Alerts on. Our emergency alerts guide explains the county's AlertSCC system.

Cooling centers

During heat events the city names its libraries as cooling centers during normal operating hours. Its October 2, 2026 hot weather notice listed all five:

Branch hours differ. Some branches close on Sundays and Mondays and Mitchell Park keeps the longest hours, so check the library's hours page before you set out. Our libraries guide describes each branch.

Santa Clara County keeps a countywide cooling center map and list on its hot weather safety page. The county says listings appear when there is an emergency heat event, so the list may be empty on an ordinary hot day. Ready.gov also suggests shopping malls and other air-conditioned public places. In Palo Alto that could mean an afternoon at Stanford Shopping Center or a movie.

Water

The city's October notice also pointed residents to Rinconada Pool and to the water play feature at Mitchell Park. Pool hours change by season, so confirm on the city's aquatics page. Our swimming pools guide lists other options.

Heat illness: what to watch for

Heat illness runs from mild to deadly. These descriptions follow Ready.gov's extreme heat page.

For where to go for care, see our urgent care and emergency rooms guide. Heat stroke is a 911 call, not an urgent care visit.

Who is most at risk

The city's heat notices single out people with limited access to cooling, unhoused people, older adults and children. The county adds people with chronic medical conditions and infants, noting that babies do not handle heat well because their sweat glands are not fully developed. People who live alone are at special risk because no one notices when they start to struggle.

• Call or visit older neighbors and relatives at least once a day during a heat wave.
• Ask whether their home has air conditioning and whether they can get to a library.
• Check that they are drinking water and that medications are stored properly.

Our resources for older adults page lists local organizations that can help.

Staying cool at home

The city's heat notices repeat a short list of habits that work.

1. Drink water before you feel thirsty. Limit alcohol, caffeine and sugary drinks.
2. Close the house in the morning. Shut blinds and drapes during the day. Open windows at night once it is cooler outside than in.
3. Time your activity. The city advises avoiding strenuous outdoor activity between 10 a.m. and 4 p.m. The county gives 10 a.m. to 3 p.m. as the hottest hours. Run or hike early.
4. Dress light. Loose, light-colored clothing and a wide-brimmed hat or umbrella outdoors.
5. Eat light. Small, frequent meals of cool foods such as fruit and salad.
6. Cool your body. A cool shower or damp towels help when you feel overheated.

Do not rely on a fan in serious heat. Ready.gov says fans move air and feel pleasant but do not lower body temperature or prevent heat illness. If indoor temperatures keep climbing, leave for a cooling center during the day.

Cars and pets

Never leave a child, an older adult or a pet in a parked car, even with the windows cracked and even for a quick errand. Check on pets often and give them plenty of water and shade. Our pets guide covers local vets.

Power use during heat

Heat waves strain the electric grid because everyone runs air conditioning at once. In past heat notices the city has warned of possible outages from that strain and asked residents to raise the thermostat slightly if it is safe to do so. It also asks people not to run major appliances during peak demand from 4 to 9 p.m.

Those hours match the city's optional time-of-use electric rate. Power costs the most from 4 to 9 p.m. every day and the least from 9 a.m. to 3 p.m., when solar power is plentiful. The city's tips fit a heat wave well:

• Pre-cool the house before 4 p.m., then let it coast through the evening.
• Charge an electric car or home battery between 9 a.m. and 3 p.m.
• Run the dishwasher, washer and dryer in the middle of the day or late at night.

Palo Alto runs its own electric utility. Our utilities guide explains rates and rebates, including heat pumps that both heat and cool. If the power does go out, our power outages guide explains how to report it.

Heat, smoke and fire

Hot spells often come with dry offshore winds and higher fire danger in the hills and the city's heat notices remind residents to review wildfire preparedness. Smoke from distant fires can arrive during the same weeks, which creates a hard choice: open the windows to cool down or keep them shut against smoke. Our air quality guide explains how to set up a clean, cool room and when to look for a filtered public space instead.

Frequently asked questions