Far North Ontario is starting Monday with an unsettled pattern stretching from Sandy Lake and Sachigo Lake eastward through Kitchenuhmaykoosib Inninuwug/Big Trout Lake and north to Wasaho Cree Nation/Fort Severn. Rain and showers are widespread this morning, with thunderstorms possible in several communities before cooler northwest winds take over. Marten Falls/Ogoki Post begins the day with sunshine, but showers and a thunderstorm risk arrive this afternoon.
The bigger weather story is the temperature drop behind this system. Tuesday will be noticeably cooler across the region, especially in KI, Sachigo Lake and Fort Severn. Wednesday remains cool and somewhat unsettled before sunshine becomes more widespread Thursday.
Today’s Weather Overview
KI / Big Trout Lake — Kitchenuhmaykoosib Inninuwug
Current Conditions
At 6:20 AM CDT, Big Trout Lake Airport was reporting light rain and 15.6°C. Humidity was 82 percent, with a barometric pressure of 100.6 kPa. Winds were from the west at 18 km/h, gusting to 35 km/h.
Monday remains mainly cloudy, with showers through the morning and into the afternoon. There is a risk of a thunderstorm early this afternoon. Winds become southwest at 20 km/h gusting to 40 before turning northwest with similar gusts. The daytime high will reach 20°C, followed by an overnight low of 11°C. Fog patches may develop overnight.
Sachigo Lake
Current Conditions
Environment Canada is using observations from Big Trout Lake Airport for Sachigo Lake. At 6:20 AM CDT, conditions there were light rain and 15.6°C, with humidity at 82 percent, pressure at 100.6 kPa, and west winds at 18 km/h gusting to 35 km/h.
Showers in the Sachigo Lake forecast are expected to end near noon, followed by cloudy skies and a 30 percent chance of additional showers. A thunderstorm is possible late this morning. Southwest winds at 20 km/h gusting to 40 will turn northwest near noon. The high will be 18°C, with a low tonight of 10°C.
Sandy Lake
Current Conditions
At 6:20 AM CDT, Sandy Lake Airport was reporting light rain and 15.0°C. Humidity was very high at 93 percent, with pressure at 100.8 kPa. Winds were from the west at 9 km/h.
Showers continue this morning before ending near noon, although there remains a 30 percent chance of showers this afternoon. There is also a risk of a thunderstorm late this morning. Northwest winds increase to 20 km/h gusting to 40 near noon. Today’s high is 20°C, while tonight falls to 10°C.
Marten Falls / Ogoki Post
Current Conditions
Ogoki Post had the brightest start among these Far North communities. At 7:00 AM EDT, Ogoki Post Airport was sunny and 11.6°C. Humidity was 94 percent, pressure was 101.0 kPa, and winds were west-southwest at 9 km/h.
The sunshine will not last all day. Clouds increase and showers are expected to begin this afternoon, with a risk of thunderstorms. Southwest winds increase to 20 km/h gusting to 40 near noon. The temperature climbs to 24°C, with a humidex of 27, before dropping to 12°C tonight.
Wasaho Cree Nation / Fort Severn
Current Conditions
At 7:00 AM EDT, Fort Severn Airport was reporting cloudy skies and 14.3°C. Humidity stood at 88 percent, barometric pressure was 100.1 kPa, and southwest winds were blowing at 11 km/h.
Showers are expected to develop this morning and end during the afternoon, with a risk of a thunderstorm early this afternoon. Southwest winds at 20 km/h gusting to 40 will shift sharply to the northwest at 30 km/h gusting to 50 near noon. The high is only 16°C, with tonight falling to 9°C. Fog patches may develop overnight.
Tomorrow’s Forecast
Expected Conditions — Tuesday, August 18
KI / Big Trout Lake: Cloudy with showers developing during the morning. Northwest winds increase to 20 km/h near noon. The high reaches only 14°C, followed by a low of 8°C Tuesday night with a 40 percent chance of showers.
Sachigo Lake: Expect showers and a cool high of just 14°C. Northwest winds develop near noon. Tuesday night remains cloudy with a 40 percent chance of showers and a low of 8°C.
Sandy Lake: Cloudy conditions continue, with showers developing during the morning. Northwest winds reach 20 km/h gusting to 40 near noon. The high is 17°C, with a Tuesday night low of 10°C and a 30 percent chance of showers.
Marten Falls / Ogoki Post: Cloudy with a 40 percent chance of showers through the morning and early afternoon, followed by a few showers. A thunderstorm is possible during the afternoon. West winds develop at 20 km/h. The high reaches 20°C, then falls to 8°C overnight.
Wasaho Cree Nation / Fort Severn: Cloudy with a 40 percent chance of showers and a cool high of only 13°C. Tuesday night brings cloudy periods, another 40 percent chance of showers and a low of 7°C.
Wednesday, August 19
Wednesday brings gradual improvement, but showers remain possible.
KI and Sachigo Lake will see a mix of sun and cloud with a 40 percent chance of showers and highs near 17°C. Overnight lows fall to 7°C.
Sandy Lake reaches 18°C with a 30 percent chance of showers, followed by a chilly clear night with a low of only 6°C.
Marten Falls/Ogoki Post reaches 19°C under a mix of sun and cloud with a 40 percent chance of showers. Wednesday night clears with a low of 6°C.
Fort Severn remains the coolest location, with cloudy skies, a 40 percent chance of showers and a high of just 12°C. The overnight low will be 7°C.
Thursday, August 20
Thursday is shaping up to be the best outdoor-weather day of the three-day outlook.
Environment Canada is calling for sunshine and highs near 19°C in KI and Sachigo Lake, 20°C in Sandy Lake, 19°C at Ogoki, and 17°C at Fort Severn.
Wardrobe Recommendations
Rain gear is the priority today. A water-resistant jacket or shell, waterproof footwear and an extra dry layer will be useful across KI, Sachigo Lake, Sandy Lake and Fort Severn. Ogoki residents will want the rain jacket handy for the afternoon even though the morning starts sunny.
Tuesday and Wednesday will feel considerably cooler, particularly during the morning and evening. A hoodie, fleece or light insulated jacket is a good addition, especially in Fort Severn where daytime temperatures remain in the low teens. Overnight lows of 6°C to 10°C across the region mean anyone travelling by boat, spending time on the land or working outdoors should carry warmer layers than might normally be expected for August.
With thunderstorms possible today in several locations, keep an eye on changing skies and the latest Environment Canada alerts before heading out on the water or on longer trips.
Weather Trivia
Mid-August already shows a significant north-to-south temperature difference across Ontario’s Far North. Environment Canada’s climate normals for this period list an average maximum of 20°C and minimum of 10°C for Big Trout Lake/Sachigo Lake, compared with only 17°C and 8°C at Fort Severn. Sandy Lake’s normal is 21°C/11°C, while Ogoki’s is approximately 20°C/9°C.
That means the cool conditions forecast for Fort Severn this week are particularly noticeable during the daytime, while the 6°C overnight lows expected around Sandy Lake and Ogoki Wednesday night will feel decidedly autumn-like.
Source: Environment and Climate Change Canada forecasts and observations issued Monday morning, August 17, 2026.
META Description
Far North Ontario weather for August 17, 2026: rain, thunderstorms and gusty winds for KI/Big Trout Lake, Sachigo Lake, Sandy Lake, Marten Falls/Ogoki Post and Wasaho Cree Nation/Fort Severn, followed by cooler temperatures Tuesday and improving weather Thursday.
