September 2025 kicked off with a stretch of unseasonably high temperatures across much of western North America. New heat records were set in British Columbia, Canada, and the U.S. Pacific Northwest as a zone of high pressure known as an omega block settled over the region for several days.
This map shows air temperatures in North America on September 3, 2025, at 2 p.m. Pacific Time, modeled at 2 meters (6.5 feet) above the ground. It was produced by a version of the GEOS (Goddard Earth Observing System) model, which uses mathematical equations to represent physical processes in the atmosphere. The darkest reds indicate areas where temperatures approached 40 degrees Celsius (104 degrees Fahrenheit).
On September 3, a new high temperature record for September in Canada—40.8°C (105.4°F)—was set in Ashcroft, British Columbia, about 200 kilometers (120 miles) northeast of Vancouver. That sort of heat is more common this time of year in parts of the U.S. Southwest, in places like Phoenix, Arizona.
Temperatures also soared east of the Cascade Range in Washington state, where Spokane tied its daily record of 36.7°C (98°F) on September 3. The previous two days, temperatures topped out at 37.2°C (99°F), the highest in September for that location in a record extending back to 1881.
The scorching start to September comes on the heels of a drier-than-normal summer in the region. The conditions have contributed to several large fires burning out of control in British Columbia at a time when it’s more typical for seasonal rains to be rolling in.
While a blocked high-pressure system concentrated heat out west, more autumn-like temperatures nosed down into the interior of the continent. The cold front’s arrival brought sharp temperature drops to Winnipeg, Manitoba, and other places across the eastern Prairies and northern Ontario. Forecasters warned of early-season frost and even snow flurries with the change in weather.
References & Resources
- KREM (2025, September 3) Late summer heat breaks all-time September heat record in Spokane. Accessed September 4, 2025.
- The Washington Post (2025, September 3) Intense heat wave hits the Pacific Northwest and southwestern Canada. Accessed September 4, 2025.
- The Weather Network (2025, September 3) September’s back-to-school tug of war: Summer heat meets fall chill. Accessed September 4, 2025.
- The Weather Network (2025, September 3) Tie no more: Canada’s all-time September heat record now belongs to one. Accessed September 4, 2025.
- Weather West (2025, August 30) An unusual weather pattern to bring extreme British Columbia/PacNW heatwave, with lesser CA heat (and the potential for a few surprises). Accessed September 4, 2025.
NASA Earth Observatory image by Michala Garrison, using GEOS-5 data from the Global Modeling and Assimilation Office at NASA GSFC. Story by Lindsey Doermann .
