September weather forecast
Thunder Bay, Canada

September signals the onset of autumn in Thunder Bay. While rainfall decreases to 72mm (2.83"), temperatures begin to fall. The diminishing daylight hours highlight the ebbing of summer. Yet the city remains a draw with its stunning foliage transformation, a spectacle enjoyed by locals and visitors alike.

Temperature

September's arrival comes with a decrease in the average high-temperature, moving from a warm 23.3°C (73.9°F) in August to a comfortable 17.7°C (63.9°F). In September, the recorded average low-temperature, of 5.5°C (41.9°F), exhibits a significant fall from the daytime highs.

Rainfall

In Thunder Bay, during September, the rain falls for 13.5 days and regularly aggregates up to 72mm (2.83") of precipitation. Throughout the year, in Thunder Bay, there are 92.6 rainfall days, and 547mm (21.54") of precipitation is accumulated.

Snowfall

Months with snowfall are January through May, September through December. September is the first month it typically snows in Thunder Bay, Canada. Throughout September, in the average 0.3 snowfall days, it receives 11mm (0.43") of snow. Throughout the year, in Thunder Bay, there are 62.7 snowfall days, and 1631mm (64.21") of snow is accumulated.

Sea temperature

The months with the warmest seawater in Thunder Bay are August and September, with an average sea temperature of 13°C (55.4°F).
Note: Swimming in 13°C (55.4°F) at temperatures under 10°C (50°F) requires thermal swimsuits; otherwise, one can face cold shock and breathing difficulty. Even brief immersion at 13°C (55.4°F) feels frosty.

Daylight

The average length of the day in September in Thunder Bay is 12h and 34min.
On the first day of the month, sunrise is at 7:15 am and sunset at 8:37 pm. On the last day of September, sunrise is at 7:56 am and sunset at 7:37 pm EDT.

Sunshine

The average sunshine in September in Thunder Bay is 5.5h.

UV index

The average daily maximum UV index in September in Thunder Bay, Canada, is 5. A UV Index reading of 3 to 5 represents a medium vulnerability from unsafe exposure to UV radiation for ordinary individuals.
Note: A maximum daily UV index of 5 during September morphs into the following directions:
Act with care - The need to guard against sun damage is communicated. Limiting exposure to the direct Sun during midday hours can help prevent harmful UV radiation effects. On bright days sunglasses that block both UVA and UVB rays should be worn. A hat with a wide brim is extremely helpful, as it can prevent roughly 50% of UV radiation from reaching the eyes. Take careful note! The UV radiation of the Sun can be nearly doubled by snow reflection.