Weather in Tri-Cities in December

A hard month. December is a hard month in Tri-Cities, and worth planning around. Highs sit at 6.7 °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 Tri-Cities's year. September is the month that works, and the swing between the two is 53 points, which is a different holiday rather than a slightly better one.

Rain on 10 days, 1 of them heavy. Enough to need a plan B, not enough to need a plan around it. Layers, and a genuinely waterproof outer — at 6.7 °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: 17 nights fall below freezing. Across the twenty years measured, the hottest December day reached 19.4 °C and the coldest night fell to -12.4 °C.

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 72 mm against 13 mm in the driest. In a month this wet, even a tame spread is a lot of rain in absolute terms — the 42 mm average is a reasonable planning figure, not a promise.

Wind is light at 8.7 km/h, so the temperature on the page is close to the temperature on your skin, and humidity runs at 79%, which at 6.7 °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: 11.8 °C in November, 6.7 here, 6.9 in January. Nothing about the timing within the month matters much.

Daylight in December

December sits at the dark end of Tri-Cities's year — 8.6 hours of daylight against 15.8 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 — 34.6 °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 Tri-Cities versus nearby

If Tri-Cities is one option among several, the nearby comparison is worth making. Spokane is the weaker option in December — 5.2 °C cooler, 4 days more rain. Portland is the weaker option in December — within a degree on temperature, 10 days more rain.

So: December is a compromise. September is 53 points better and is what Tri-Cities 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 Tri-Cities

See all twelve months in Tri-Cities, or where else to go in December.