| Month | High | Low | Rain | Wet days | Score |
|---|---|---|---|---|---|
| January | 15° | 4.9° | 133.7mm | 12.3 | 59 |
| February | 17.3° | 5.2° | 125.3mm | 10.1 | 71 |
| March | 19.6° | 6.3° | 89.5mm | 9.6 | 80 |
| April | 22.3° | 7.5° | 44.5mm | 6.1 | 88 |
| May | 24.9° | 9.8° | 25.4mm | 3.3 | 93 |
| June | 27.9° | 12.1° | 3.9mm | 0.8 | 95 |
| July | 28.6° | 13.1° | 0mm | 0 | 94 |
| August | 28.7° | 13.1° | 1.5mm | 0.2 | 93 |
| September | 29.1° | 12° | 3.3mm | 1.1 | 89 |
| October | 25.6° | 9.7° | 33.8mm | 3.3 | 93 |
| November | 19° | 6.6° | 74mm | 8.2 | 80 |
| December | 14.8° | 4.6° | 145.3mm | 12 | 59 |
January in Napa averages a daily high of 15°C with nights around 4.9°C. Expect roughly 12.3 wet days totalling 133.7mm. Generally workable, with some weather to plan around.
February in Napa averages a daily high of 17.3°C with nights around 5.2°C. Expect roughly 10.1 wet days totalling 125.3mm. Generally workable, with some weather to plan around.
March in Napa averages a daily high of 19.6°C with nights around 6.3°C. Expect roughly 9.6 wet days totalling 89.5mm. Comfortable conditions for being outdoors all day.
April in Napa averages a daily high of 22.3°C with nights around 7.5°C. Expect roughly 6.1 wet days totalling 44.5mm. Comfortable conditions for being outdoors all day.
May in Napa averages a daily high of 24.9°C with nights around 9.8°C. Expect roughly 3.3 wet days totalling 25.4mm. Comfortable conditions for being outdoors all day.
June in Napa averages a daily high of 27.9°C with nights around 12.1°C. Rain is rare — about 0.8 wet days and 3.9mm across the month. Comfortable conditions for being outdoors all day.
July in Napa averages a daily high of 28.6°C with nights around 13.1°C. Rain is rare — about 0 wet days and 0mm across the month. Comfortable conditions for being outdoors all day.
August in Napa averages a daily high of 28.7°C with nights around 13.1°C. Rain is rare — about 0.2 wet days and 1.5mm across the month. Comfortable conditions for being outdoors all day.
September in Napa averages a daily high of 29.1°C with nights around 12°C. Rain is rare — about 1.1 wet days and 3.3mm across the month. Comfortable conditions for being outdoors all day.
October in Napa averages a daily high of 25.6°C with nights around 9.7°C. Expect roughly 3.3 wet days totalling 33.8mm. Comfortable conditions for being outdoors all day.
November in Napa averages a daily high of 19°C with nights around 6.6°C. Expect roughly 8.2 wet days totalling 74mm. Comfortable conditions for being outdoors all day.
December in Napa averages a daily high of 14.8°C with nights around 4.6°C. Expect roughly 12 wet days totalling 145.3mm. Generally workable, with some weather to plan around.
Each month scores out of 100. It starts at 100 and loses points for daytime highs outside a 20–27°C band, for wet days, and for nights below 2°C. Nothing else is weighted in — no crowd data, no prices, no opinion. Napa peaks at 95.
Based on 30 years of records, April–October scores highest for comfort in Napa, balancing daytime temperature against rainfall.
September is the warmest, averaging a daily high of 29.1°C.
December is the wettest, averaging 145.3mm of rain across roughly 12 wet days.
December is the coolest month, with average daily highs around 14.8°C.