UV Index Today in Palo Alto, California

Current UV
Today's Max

Hourly UV Forecast

low moderate high very high extreme

Surface Type

Reflective surfaces increase your UV exposure — snow reflects up to 90%, sand about 20%.

Safe Exposure Time

Estimated burn times based on the Fitzpatrick scale for skin color and today's maximum UV index of . Tap your skin type:

Very fair skin, always burns, never tans

Time until burn
With SPF 15*
With SPF 30*

*Assumes proper application of broad-spectrum sunscreen with reapplication every 2 hours. Estimates follow WHO guidance and satellite-derived data — see how our data works.

Sun Times

Dawn
Sunrise
Solar Noon
Sunset
Dusk
Day Length
Morning Golden Hour Ends
Evening Golden Hour

Important Safety Information

General Guidelines

These exposure times are estimates based on scientific research and should be used as general guidelines only. Individual responses to UV exposure may vary.

Affecting Factors

UV exposure is affected by: time of day, season, altitude, cloud cover, reflection from surfaces, and individual skin sensitivity.

Protection Tips

Seek shade during peak UV hours (10 AM - 4 PM), wear protective clothing, use broad-spectrum sunscreen, and monitor the UV index regularly.

Medical Advice

Consult a healthcare provider for personalized sun protection advice, especially if you have a history of skin conditions or take medications that increase sun sensitivity.

Palo Alto's UV Climate

Palo Alto sits on the sheltered bay side of the Santa Cruz Mountains, which block most of the coastal fog that cools San Francisco — giving the town a sunnier, warmer climate than its neighbors over the hill. Stanford's campus life, the lunchtime cycling culture on Foothill Expressway, and dawn-to-dusk youth sports put this community outdoors year-round under a sun that runs high from mid-spring through fall.

Average Annual UV Index

6.9

Peak UV Season

April - October

Sunny Days per Year

261

Typical UV Index by Season in Palo Alto

Season Typical Midday UV Protection Needed
Summer Very High (8-10) SPF 30+, hat, sunglasses; shade from 10 AM – 4 PM
Spring & Fall Moderate to High (5-8) SPF 30+ for extended time outdoors
Winter Low to Moderate (2-4) Sunscreen for long midday exposure; more on snow

UV Index in Nearby Cities

Practical Tips for Outdoor Activities

Make the most of outdoor activities while staying safe in Santa Clara County:

UV and Weather in Santa Clara County

Learn about Santa Clara County's unique climate patterns, UV radiation levels, and how they affect your daily life. Enter your zip code for location-specific weather radar data and UV forecasts to help you make informed decisions about outdoor activities and sun protection.

Climate and UV Patterns

Palo Alto's Mediterranean climate delivers dry, reliably sunny summers with midday UV index values of 8-10. The mountain barrier means morning fog is thinner and burns off earlier than on the coast, exposing more of the peak UV window. The long rainless season from April through October keeps outdoor routines uninterrupted — and cumulative exposure high — for months at a stretch.

UV Index and Health Impact

Understanding UV radiation levels is crucial for protecting your health. Typical clear-day UV index values in Palo Alto through the year:

  • Summer: Very High (8-10)
  • Spring/Fall: Moderate to High (5-8)
  • Winter: Low to Moderate (2-4)
  • Peak UV hours: 10 AM - 4 PM
  • Cloud cover can reduce UV by 20-40%, but does not eliminate it
  • Clear skies bring maximum UV exposure

Local Weather Patterns

Summer mornings may start with high overcast spilling over the mountains, but late mornings through afternoons run clear and mild — comfortable cycling and running weather that encourages long midday exposure. Fall stays warm and bright through October. Winter alternates rainy systems with crisp, sunny spells where midday UV reaches the moderate range, keeping year-round athletes in the exposure game.

Frequently Asked Questions About UV in Palo Alto

What is the UV index in Palo Alto today?

The live UV index for Palo Alto, CA is shown at the top of this page and updates throughout the day, along with today's maximum and an hourly forecast.

When is the sun strongest in Palo Alto?

UV radiation is strongest between 10 AM and 4 PM. Palo Alto's peak UV season runs April - October, when the midday index typically reaches Very High (8-10).

How high does the UV index get in Palo Alto?

Summer days in Palo Alto typically reach Very High (8-10). Spring and fall usually bring Moderate to High (5-8), while winter values are typically Low to Moderate (2-4).

Do I need sunscreen in Palo Alto during winter?

Clear winter days in Palo Alto reach low-moderate midday UV — worth sunscreen for long rides, runs, and sideline afternoons.

How sunny is Palo Alto compared to other cities?

Palo Alto averages about 261 sunny days per year with an average annual UV index around 6.9.