THUNDER BAY — Thunder Bay begins Monday with thunderstorms, light rain and saturated air as an active weather system moves through the region.
The Severe Thunderstorm Watch has ended.
Severe Thunderstorm Watch
Thunder Bay is under a yellow severe thunderstorm watch.
Thunderstorms may produce sudden heavy rainfall, frequent lightning and strong wind gusts. The rapidly strengthening west wind could also make travel difficult, particularly for high-profile vehicles and anyone using area lakes.
Residents should secure lightweight outdoor objects, including patio furniture, umbrellas and garbage containers.
Boaters should closely monitor conditions and be prepared to return to shore quickly. Thunderstorms can develop or intensify rapidly, even when conditions appear manageable nearby.
Remember: when thunder roars, go indoors.
Environment Canada has issued two weather alerts for the city: a yellow severe thunderstorm watch and a yellow air-quality warning. Residents should prepare for additional thunderstorms, strong wind gusts and periods of wildfire smoke throughout the day.
Conditions will turn cooler and windy Tuesday before sunshine returns Wednesday.
Today’s Weather Overview
Current Conditions
At 7:00 a.m. EDT on Monday, July 20, Thunder Bay was reporting a thunderstorm with light rain showers and a temperature of 15°C.
The dew point was also 15°C, producing humidity of 100 per cent. Winds were from the north-northeast at 14 km/h.
Barometric pressure was 100.4 kPa and falling, reflecting the unsettled weather moving across the area.
Visibility was reduced to five kilometres.
Monday Forecast
The morning showers are expected to end before mainly cloudy skies develop. There will remain a 60 per cent chance of showers throughout the day, along with a continued risk of thunderstorms.
Local wildfire smoke may also affect visibility and air quality.
Winds will become southerly at 20 km/h late this morning before shifting sharply to the west at 50 km/h, with gusts reaching 70 km/h.
The temperature will climb to 27°C. High humidity will make it feel closer to 35.
The UV index will be 7, or high, during brighter breaks in the cloud cover.
Monday Night
Tonight will remain mainly cloudy, with a 60 per cent chance of showers.
There will be a risk of thunderstorms during the evening and again after midnight. Local smoke will remain possible.
West winds of 50 km/h, gusting to 70, will become northwest at 30 km/h, gusting to 60, during the evening.
The overnight low will be 15°C.
Three-Day Thunder Bay Forecast
Tuesday, July 21
Tuesday will be cloudy, with a 30 per cent chance of showers during the morning.
Local wildfire smoke may continue to affect the Thunder Bay area.
Strong northwest winds will blow at 40 km/h, with gusts reaching 60 km/h. The daytime high will be 21°C.
The UV index will fall to 4, or moderate.
Skies will clear Tuesday night as the temperature drops to a cool 9°C.
Wednesday, July 22
Wednesday will bring a return to sunny skies and warmer temperatures.
The daytime high will reach 25°C.
Clouds will begin to increase Wednesday night, with a 30 per cent chance of showers and an overnight low of 13°C.
Thursday, July 23
Thursday will feature a mix of changing conditions, with a 30 per cent chance of showers.
The daytime high will rise to 27°C.
There will remain a 30 per cent chance of showers Thursday night, with a low of 14°C.
Wildfire Smoke and Air Quality
A yellow air-quality warning remains in effect because of wildfire smoke.
Local smoke is expected today and Tuesday. Smoke concentrations and visibility may change quickly depending on wind direction, rainfall and nearby thunderstorm activity.
People may experience irritated eyes, a sore throat, coughing or headaches. Those with asthma, heart disease, lung conditions or other chronic illnesses may be more strongly affected.
Older adults, pregnant people, infants, children and outdoor workers should reduce strenuous outdoor activity when smoke is noticeable.
Keep windows and doors closed when practical. A portable air cleaner or an appropriate high-efficiency ventilation filter can help reduce fine smoke particles indoors.
A properly fitted N95 or equivalent respirator can reduce exposure for people who must spend time outside.
Travel and Outdoor Safety
The combination of thunderstorms, heavy showers, smoke and wind gusts of up to 70 km/h could create rapidly changing driving conditions.
Motorists should be prepared for reduced visibility, standing water and fallen branches. Allow additional stopping distance and avoid driving through flooded sections of road.
Outdoor events, construction sites and recreational programs should have a plan to move participants indoors quickly if lightning approaches.
Conditions on Lake Superior and inland lakes may become dangerous as winds strengthen.
Wardrobe Recommendations
Wear light, breathable clothing today because the humidex will reach 35.
Carry a waterproof jacket or umbrella, but avoid using an umbrella during strong winds or thunderstorms.
Water-resistant footwear will be useful during periods of rain.
A hat, sunglasses and sunscreen are still recommended because the UV index will be high when the sun appears.
A wind-resistant jacket will be important later today and Tuesday as gusts increase.
Keep a sweater or warmer jacket available Tuesday night, when temperatures will fall to 9°C.
Weather Trivia
A relative humidity reading of 100 per cent does not necessarily mean that it is raining continuously. It means the air is fully saturated at the measured temperature.
Thunder Bay’s temperature and dew point were both 15°C at 7:00 a.m. Monday, producing the 100 per cent humidity reading and helping support fog, low cloud, rain and thunderstorm development.
In Summary: Thunder Bay weather for July 20, 2026: Severe thunderstorm watch, wildfire smoke, showers, humidex of 35 and west wind gusts reaching 70 km/h, followed by a cooler Tuesday.
