Palo Alto weather in April

April is the month many locals would pick if they could only have one. Afternoons settle near 70°F. Rain shrinks to a few light showers. The hills are still green, gardens are in full bloom and evenings stay light until nearly 8 p.m. The main things to plan around are cool mornings, breezy afternoons and pollen.

The averages below are NOAA's 1991 to 2020 climate normals for the Palo Alto station (USC00046646), on the flats at about 25 feet. NOAA rates the station's values "representative" because its record has gaps, which is a reminder that a tenth of a degree here or there means little. Sun times are calculated for central Palo Alto for April 2027 and checked against published tables. They are averages, not forecasts. Compare all twelve months on our weather page.

April by the numbers

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

Rain: the last of the season

April averages 0.97 inches at the Palo Alto station, less than half of March. Rain falls on about 5 days. Only about 3 bring a tenth of an inch or more. The median April gets 0.56 inches. In one April out of four the station records less than 0.22 inches. In one out of four it gets more than 1.30.

Most April rain comes as showers behind a weak front. A late storm can still deliver a soaking day, especially early in the month. After mid April, long dry spells are the norm. For many years the last measurable rain of the season falls in April or May. The next real storm does not come until October or November.

Daylight

April days are long and still growing. Sunrise moves from about 6:54 a.m. on April 1 to about 6:15 a.m. by April 30. Sunset moves from about 7:31 p.m. to about 7:57 p.m. Day length grows from about 12 hours 37 minutes to 13 hours 43 minutes.

That leaves plenty of light for an after-work hike. Stanford posts hours of 6 a.m. to 7:30 p.m. for the Dish from April through August. Midpen preserves stay open until half an hour after sunset.

Fog, wind and air quality

Fog

April is mostly fog free on the bay side of the mountains. Toward the end of the month, low clouds start forming over the ocean on some nights and pushing into San Francisco and the coast. On a few mornings a thin gray layer may reach Palo Alto, usually burning off by 10 a.m. The real marine layer season is still a month or two away.

Wind

Afternoon wind is the defining April feature. As the Central Valley warms, cool ocean air rushes toward it through gaps in the Coast Ranges. In Palo Alto that shows up as a steady northwest breeze off the bay most afternoons. Cyclists on the Bay Trail feel it heading north. Sailors and windsurfers welcome it.

Air quality and pollen

The Air District's summer Spare the Air season for ozone usually runs from April through October, but April ozone alerts are rare because temperatures are mild. Wildfire smoke is not a typical April concern. Pollen is. Oak, grass and other spring pollen peaks in April for many people, especially on dry, windy days. If you have allergies, check the pollen count and the AQI on AirNow before a long hike.

Microclimates in April

The spread between the bay and inland areas starts to grow in April. Moffett Field, right on the bay, averages a high of 68.0°F, more than a degree and a half cooler than the Palo Alto station's 69.6°F, because the afternoon breeze comes straight off the water. Its nights are warmer, with a low of 48.9°F against 45.3°F in Palo Alto.

Within Palo Alto the same pattern applies street by street. The Baylands and the neighborhoods east of Highway 101 run cooler and windier in the afternoon. Downtown, Professorville and Stanford are a little warmer and calmer. The foothills along Arastradero and Page Mill roads heat up most at midday on south-facing slopes, then cool quickly after sunset.

Up on Skyline Boulevard, above 2,000 feet, April can bring both the clearest days of the year and the occasional cold, foggy morning when the first marine layer spills over the ridge. Wildflowers bloom later up there, so the ridge preserves are at their best from late April into May.

How April compares with San Francisco and San Jose

April is when the famous Bay Area temperature gap opens. Downtown San Francisco averages a high of 63.0°F, more than six degrees cooler than Palo Alto. The city's ocean winds and early fog keep it cool while the Peninsula warms. San Jose is close to Palo Alto by day at 69.2°F and about three degrees warmer at night.

Rain is light everywhere. San Francisco averages 1.60 inches in April, San Jose 1.07 and Palo Alto 0.97. Pack a warm layer for any day in the city, even if Palo Alto feels like early summer.

The coast in April

April is the start of the coldest water of the year along the coast. NOAA's buoy west of San Francisco averages 52.6°F in April. The long term average dips again in May. Strong northwest winds push surface water offshore and pull cold, nutrient-rich water up from below. That upwelling feeds the coastal food web and helps explain why humpback whales arrive offshore in late spring. It also means Half Moon Bay can be windy and chilly on a day when Palo Alto is in the 70s. The Monterey buoy averages 54.2°F.

Inside the bay, NOAA's Redwood City reading averages 61.0°F in April, already several degrees warmer than the ocean. Shallow bay water warms quickly under spring sun.

What to pack for April

• Layers. A sweater or light jacket for mornings in the 40s and evenings in the 50s.
• Short sleeves for afternoons near 70°F.
• A windbreaker for the Bay Trail, the coast or San Francisco.
• A compact umbrella just in case, though many Aprils need it only once or twice.
• Sunscreen and a hat. The sun is high and the air is clear.

What April weather is good for

Almost everything outdoors. Our April trip guide covers spring break dates and events. Weather-driven ideas:

1. Gardens in bloom. Gamble Garden is at its spring peak and free to visit.
2. Wildflowers on the ridge. The low hills peak first, then the high preserves. Russian Ridge is a favorite for late April. Our wildflower guide has the details.
3. Bike rides with a tailwind. Ride the Bay Trail north in the morning and come back before the afternoon wind builds, or see our biking guide for inland routes.
4. A coast day. Combine wildflowers on the bluffs with a meal at the harbor on a Half Moon Bay day trip. Bring a warm layer for the wind.

April is a popular month for visits, with spring break and campus tours. If your dates are set, it pays to compare Palo Alto hotels early.

Frequently asked questions