Weather in Thunder Bay in August

Prime time. August is about as good as Thunder Bay gets. Highs average 24.4 °C, lows 13.6 °C, and rain falls on 12 days — nothing in the month is working against you.

August is the highest-scoring month of the twelve. The nearest rival is July, and the month at the other end of the year is December.

Rain on 12 days, 1 of them heavy. Enough to need a plan B, not enough to need a plan around it. Nothing specialised needed — this is the month you pack for the trip rather than for the weather.

What the averages hide

The averages here are honest — no hidden extremes worth planning around. Across the twenty years measured, the hottest August day reached 33.6 °C and the coldest night fell to 5.9 °C, and the wettest single day dropped 26 mm — roughly 44% of the month's rain in one day.

August is statistically steady but not small: the year-to-year variation is modest in relative terms, yet the wettest August on record still delivered 104 mm against 18 mm in the driest. In a month this wet, even a tame spread is a lot of rain in absolute terms — the 59 mm average is a reasonable planning figure, not a promise.

Wind is light at 2 km/h, so the temperature on the page is close to the temperature on your skin, and humidity is unremarkable at 74%.

How August sits in the year

Temperatures hold steady either side: 24.7 °C in July, 24.4 here, 19.6 in September. Nothing about the timing within the month matters much.

Daylight in August

14.4 hours of daylight, losing 1.5 hours across the month. That is between Thunder Bay's extremes of 16.1 and 8.4 hours, so days are long enough not to constrain the plan.

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

Peak season. Expect the highest prices of the year and to be booking well ahead.

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

August 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 — 2.7 °C warmer, the same number of rain days. Milwaukee is close enough to be a coin toss — 3.1 °C warmer, the same number of rain days.

So: August is the answer for Thunder Bay. If it is booked out or priced out, July is the next best thing at 4 points behind, and December is the month to keep off the shortlist.

Every month in Thunder Bay

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