As of 3:01 PM PDT on May 20, 2026, all 11 cities in Napa County, CA in our database have a UV Index reading of High. The city with the highest UV Index reading right now is St. Helena, CA with a reading of 6.4.
Over the next 24 hours, the highest UV Index reading in Napa County, CA is expected to be 9 in St. Helena between 1:00 PM - 2:00 PM PDT tomorrow.
| Range | 0 - 2 | 3 - 5 | 6 - 7 | 8 - 10 | 11+ |
|---|---|---|---|---|---|
| Color | |||||
| Risk | Low | Moderate | High | Very High | Extreme |