Thunder Bay Weather Desk Update – Warmth Building, But Showers and Thunderstorms Still in the Mix

THUNDER BAY – WEATHER DESK – Thunder Bay is waking up to a damp and mild Sunday morning, with spring continuing its slow transition toward summer. While today brings clouds, the possibility of showers, and even a late-day thunderstorm risk, residents can also look ahead to a major warm-up arriving by midweek.

It feels very close with the humidity at 97%. You won’t need gloves but you will appreciate that you are wearing a windbreaker and fleece jacket.

At 8:00 AM EDT, Thunder Bay Airport reported a temperature of 7.9°C with very moist air across the region.

Current conditions include:

Temperature: 7.9°C
Humidity: 97%
Dew Point: 7.4°C
Wind: West 4 km/h
Pressure: 101.5 kPa
Visibility: Moist conditions with fog patches lingering in some areas

The near-saturated humidity levels explain the damp morning feel across the city, while weak winds are allowing lingering low cloud and patchy fog to slowly clear.

Today’s Weather Overview

Sunday will feature mainly cloudy skies with a 40 percent chance of showers early this morning and again late this afternoon.

Forecasters are also tracking a risk of thunderstorms developing late this afternoon, so anyone planning outdoor activities should keep an eye on changing skies.

Fog patches will dissipate through the morning.

Forecast High

20°C

UV Index

5 – Moderate

For late May in Thunder Bay, this is a fairly typical spring setup — moisture, instability, and fluctuating temperatures battling for control.

Tonight – Fog Returns

Tonight will turn partly cloudy with lingering weather risks early.

40 percent chance of showers early this evening
Risk of a thunderstorm early tonight
Fog patches redevelop after midnight

Overnight Low

5°C

Motorists heading out late tonight or early Monday morning should prepare for reduced visibility in localized fog areas.

Monday Forecast – Another Storm Chance Before Sunshine Takes Over

Monday continues the unsettled trend.

Expect mainly cloudy skies with a 40 percent chance of afternoon showers and another risk of thunderstorms late in the day.

Morning fog patches will clear.

Monday High

22°C

UV Index

7 – High

Monday night remains mild.

Cloudy periods
30 percent chance of showers
Low 8°C

Extended Forecast – Summer Finally Knocking on Thunder Bay’s Door

Tuesday, May 26

☀️ Sunny
High 27°C
Low 7°C

Wednesday, May 27

☀️ Sunny
High 23°C
Low 8°C

Thursday, May 28

☀️ Sunny
High 25°C
Low 8°C

Friday, May 29

☀️ Sunny
High 23°C
Low 6°C

Saturday, May 30

☀️ Sunny
High 24°C

After weeks of what often felt more like April than late May, Thunder Bay appears poised for a much-needed stretch of spring warmth.

Lake Superior Marine Weather Outlook

Boaters on western Lake Superior should remain alert for changing conditions today and Monday.

Patchy fog early today may reduce visibility near shorelines and harbour areas. Thunderstorm development late Sunday and Monday could also bring sudden gusty winds and rapidly changing wave conditions.

Calmer and more stable marine weather arrives Tuesday into the latter half of the week as high pressure settles across Northwestern Ontario.

Wardrobe Recommendations

Today: Light layers and a waterproof jacket remain smart choices. Keep rain gear handy if spending extended time outdoors.

Monday: Similar conditions — comfortable but variable.

Tuesday onward: Sunglasses, sunscreen, and lighter summer clothing may finally become the go-to choices.

Weather Trivia

Thunder Bay’s location beside Lake Superior often delays spring warming compared to inland Northwestern Ontario communities. Cold lake water acts like nature’s air conditioner well into May and sometimes June — one reason why inland communities can reach summer temperatures while the shoreline remains significantly cooler.

Overview

Thunder Bay Weather Desk Update for May 24, 2026: Showers and thunderstorm risks continue Sunday and Monday before sunshine and summer warmth arrive with highs reaching 27°C.

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