Weather in Napa in December

Shoulder season. December is shoulder season in Napa — cheaper, quieter, and a genuine gamble. Highs sit at 14.4 °C and the day is short; this is an indoors-with-excursions month, not an outdoors-all-day one.

December ranks 12 of 12 — near the bottom of Napa's year. May is the month that works, and the swing between the two is 40 points, which is a different holiday rather than a slightly better one.

This is wet-season rain: 12 wet days and 6 genuinely heavy ones, which in this climate means concentrated downpours rather than all-day grey. The pattern is usually a clear morning and a loud afternoon, so front-load the day and stop fighting the 3pm hour. Layers, and a genuinely waterproof outer — at 14.4 °C the difference between a good day and a miserable one is entirely down to what you are wearing.

What the averages hide

The averages here are honest — no hidden extremes worth planning around. Across the twenty years measured, the hottest December day reached 23.1 °C and the coldest night fell to -2.7 °C, and the wettest single day dropped 109 mm — roughly 67% of the month's rain in one day.

December is moderately variable: 2 mm in the driest year against 392 mm in the wettest, around an average of 163 mm. Roughly two Decembers in three land near that average, and the third does something else entirely.

Wind is light at 5.6 km/h, so the temperature on the page is close to the temperature on your skin, and humidity runs at 81%, which at 14.4 °C means damp rather than muggy — the kind of cold that gets into a coat and stays there.

How December sits in the year

Temperatures hold steady either side: 19.5 °C in November, 14.4 here, 14.6 in January. Nothing about the timing within the month matters much. Rain has already shifted: 5 days more than November had.

Daylight in December

December sits at the dark end of Napa's year — 9.5 hours of daylight against 14.8 at midsummer, holding steady all month. Sightseeing days are genuinely shorter, and an itinerary built for summer will not fit.

An inland climate

With no coast nearby, the year swings a fair way — 28.6 °C between the warmest afternoons and the coldest nights, wider than any coastal city at this latitude would manage.

How busy it gets

Off season. The genuine off season: cheapest by a distance, with the caveat that some tours and restaurants close entirely.

Crowd levels are estimated from climate desirability and school-holiday calendars, not from visitor numbers.

December in Napa versus nearby

If Napa is one option among several, the nearby comparison is worth making. San Francisco is close enough to be a coin toss — within a degree on temperature, the same number of rain days. Sacramento is close enough to be a coin toss — within a degree on temperature, 1 day less rain.

So: December is a compromise. May is 40 points better and is what Napa is actually like at its best — worth moving the trip for if that is possible, and worth adjusting expectations for if it is not.

Every month in Napa

See all twelve months in Napa, or where else to go in December.