Weather in Seattle in December

The month to avoid. Of the twelve, December is the one to avoid. Highs sit at 7 °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 Seattle's year. July is the month that works, and the swing between the two is 71 points, which is a different holiday rather than a slightly better one.

Rain on 19 days, 6 of them heavy. Enough to need a plan B, not enough to need a plan around it. Layers, and a genuinely waterproof outer — at 7 °C the difference between a good day and a miserable one is entirely down to what you are wearing.

What the averages hide

Averages flatten a month, and this one hides a few things: 7 nights fall below freezing; the day barely swings — 5 °C between the overnight low and the afternoon high. Across the twenty years measured, the hottest December day reached 15.8 °C and the coldest night fell to -10.1 °C, and the wettest single day dropped 65 mm — roughly 37% of the month's rain in one day.

December is statistically steady but not small: the year-to-year variation is modest in relative terms, yet the wettest December on record still delivered 323 mm against 72 mm in the driest. In a month this wet, even a tame spread is a lot of rain in absolute terms — the 175 mm average is a reasonable planning figure, not a promise.

Wind is light at 3.1 km/h, so the temperature on the page is close to the temperature on your skin, and humidity runs at 90%, which at 7 °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: 10.4 °C in November, 7 here, 7.8 in January. Nothing about the timing within the month matters much.

Daylight in December

December sits at the dark end of Seattle's year — 8.5 hours of daylight against 16 at midsummer, holding steady all month. Sightseeing days are genuinely shorter, and an itinerary built for summer will not fit.

An inland climate

Despite being inland, the year stays fairly even: 21.9 °C between the year's warmest afternoons and coldest nights.

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 Seattle versus nearby

If Seattle is one option among several, the nearby comparison is worth making. Maple Ridge is close enough to be a coin toss — within a degree on temperature, 2 days more rain. Vancouver is close enough to be a coin toss — 2.8 °C cooler, 2 days more rain.

So: December is a compromise. July is 71 points better and is what Seattle 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 Seattle

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