Weather in Thunder Bay in December

The month to avoid. December is the month most people should skip in Thunder Bay. Highs sit at -5 °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 Thunder Bay's year. August is the month that works, and the swing between the two is 54 points, which is a different holiday rather than a slightly better one.

Rain on 8 days, 0 of them heavy. Enough to need a plan B, not enough to need a plan around it. Layers, and a genuinely waterproof outer — at -5 °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: 30 nights drop below freezing, so anything left outside stays frozen. Across the twenty years measured, the hottest December day reached 6.3 °C and the coldest night fell to -33.9 °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 63 mm against 20 mm in the driest. In a month this wet, even a tame spread is a lot of rain in absolute terms — the 33 mm average is a reasonable planning figure, not a promise.

Wind is light at 4.6 km/h, so the temperature on the page is close to the temperature on your skin, and humidity runs at 93%, which at -5 °C means damp rather than muggy — the kind of cold that gets into a coat and stays there.

How December sits in the year

The month is on the way down: 7.8 °C cooler than November, with January dropping another 3.5 °C. The first week and the last are not the same trip.

Daylight in December

December sits at the dark end of Thunder Bay's year — 8.4 hours of daylight against 16.1 at midsummer, holding steady all month. Sightseeing days are genuinely shorter, and an itinerary built for summer will not fit.

An inland climate

Thunder Bay has no sea to moderate it, and it shows: 42 °C separates the hottest afternoon of the year from the coldest night. That is a genuinely continental range, and it means summer and winter here are barely the same place.

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 Thunder Bay versus nearby

If Thunder Bay is one option among several, the nearby comparison is worth making. Minneapolis is close enough to be a coin toss — 2.2 °C warmer, 2 days less rain. Milwaukee is close enough to be a coin toss — 5.5 °C warmer, 1 day less rain.

So: December is a compromise. August is 54 points better and is what Thunder Bay 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 Thunder Bay

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