Palo Alto weather in August

August in Palo Alto looks a lot like July on paper: warm afternoons, cool nights and essentially no rain. The differences are subtle but useful. Evenings start getting shorter, the bay water reaches its warmest and the region moves into the part of the year when wildfire smoke is most likely. Most August days are simply sunny and in the upper 70s.

The temperature and rain figures are NOAA's 1991 to 2020 climate normals for the Palo Alto station (USC00046646), which stands on the flats at about 25 feet. NOAA calls these values "representative" because the station's record is incomplete, so small month to month differences are not precise. Sunrise and sunset times are calculated for central Palo Alto for August 2027 and match published tables within a minute. Treat everything here as a typical August, not a forecast. Our weather guide shows all twelve months.

August by the numbers

There is no published long term sea temperature for Half Moon Bay. The ocean row is NOAA's average for its buoy about 18 nautical miles west of San Francisco.

Warm and dry

August averages 0.03 inches of rain. The median is zero and the average count of days with measurable rain is 0.2. In practice, August rain in Palo Alto comes from one of two rare sources: a fog drizzle on a deep marine layer morning or moisture from summer thunderstorms drifting up from the south.

Those thunderstorms matter more for fire than for rain. In mid August 2020, a rare outbreak of dry lightning struck across Northern California and started hundreds of fires, including the CZU Lightning Complex in the Santa Cruz Mountains of San Mateo and Santa Cruz counties. It burned for weeks and filled the region with smoke.

Temperatures run close to July. The Palo Alto station averages 12.2 days at 80°F or hotter and 2.0 days at 90°F or more. A 100°F day averages 0.1 times in August, or about once a decade.

Shorter evenings

August is when the shrinking days become noticeable. Sunrise moves from about 6:13 a.m. on August 1 to about 6:38 a.m. on August 31. Sunset moves from about 8:17 p.m. to about 7:39 p.m. Daylight drops from about 14 hours 4 minutes to 13 hours 1 minute.

Stanford keeps summer hours of 6 a.m. to 7:30 p.m. for the Dish through August. By late in the month the Dish closes only minutes before sunset.

Fog, smoke and air quality

Fog

August is still deep in the coastal fog season. San Francisco, Pacifica and Half Moon Bay can spend days under a gray marine layer. Palo Alto, behind the Santa Cruz Mountains, gets the occasional gray morning when the fog is deep enough to spill over the ridge, then sunny afternoons. Toward the end of August the marine layer often starts thinning as the offshore pattern begins to shift.

Wildfire smoke

Late summer through fall is the main wildfire smoke season for the Bay Area. Smoke can come from fires hundreds of miles away when winds line up. It can sit under the marine inversion for days. Some years bring none. Others bring weeks of hazy, orange-tinted skies. When smoke arrives, check the AirNow Fire and Smoke Map, limit hard exercise and set up a room with filtered air. Our air quality guide explains how.

Fire weather

The hills are fully dry by August. The National Weather Service issues Red Flag Warnings when wind and low humidity combine with dry fuel. Stanford can restrict access to the Dish during them. It is a good month to review the city's wildfire advice in our emergency preparedness guide, especially if you live near the foothills.

Microclimates in August

The bay breeze sets the pattern. Moffett Field, on the shoreline in Mountain View, averages an August high of 76.9°F and a low of 59.0°F, against 78.7°F and 55.3°F at the Palo Alto station. Its nights are nearly four degrees warmer because the bay, now at its warmest, releases heat after dark.

Within town, the Baylands are cooler and windier in the afternoon than downtown. Stanford and the neighborhoods near Junipero Serra Boulevard warm a little more. The foothills heat fastest on still days. Exposed grassland at Pearson-Arastradero can feel much hotter than the reading at the station.

On Skyline Boulevard, above 2,000 feet, August can mean sun above the fog at one moment and wind-driven mist the next. The ridge is often cooler than the flats in the afternoon and warmer than them at night, because it sits above the shallow cool layer that pools in the valley after dark.

How August compares with San Francisco and San Jose

Downtown San Francisco averages an August high of 67.9°F, about 11 degrees cooler than Palo Alto. Its fog and wind make it feel colder still, especially in the evening. San Jose is the warmest of the three at 81.4°F, with nights in the upper 50s.

The practical takeaway: pack differently for each city on the same day. Shorts and sunglasses in Palo Alto and San Jose, a warm jacket and long pants in San Francisco. Rain is negligible in all three.

Water temperatures in August

The ocean is warming but still cold. NOAA's buoy west of San Francisco averages 57.2°F in August and the Monterey buoy 59.0°F. NOAA has no long term Half Moon Bay figure, but late summer and early fall usually bring the warmest surf of the year there, still well below 60°F. Wetsuits are standard.

The bay is a different story. NOAA's Redwood City reading averages 72.0°F in August, the warmest of any month. That makes August a pleasant time to paddle from the Baylands or Redwood City, as long as you go early before the afternoon wind. Offshore, humpback whales feed in Monterey Bay from late spring through fall. If you want to see them, you can book a Monterey whale watching tour.

What to pack for August

• Summer clothes for afternoons near 80°F.
• A light jacket for evenings in the 50s.
• Warm layers for San Francisco and the coast.
• N95 masks if you are sensitive to smoke. Cloth masks do not filter it.
• Sun protection and water for exposed trails.

What August weather is good for

August is great for long outdoor days, with a backup plan for smoke. Our August trip guide covers festivals and school dates. Weather-driven ideas:

1. Meteor watching. The Perseids peak in mid August, when warm nights make the ridge comfortable. See our stargazing guide.
2. Paddling on warm bay water. Go in the morning. Our kayaking and paddling guide lists launch spots.
3. Whales and the Monterey coast. Summer and fall are humpback season. Our whale watching guide and Monterey and Carmel day trip have details.
4. Smoke days indoors. Museums, libraries and movie theaters with filtered air are the best plan when the AQI climbs.

Keep an eye on the AQI in the morning and decide then whether to hike or head indoors.

Frequently asked questions