+38.6°C in Canada in September – Levels never before recorded in Autumn

Western North America is in the grip of a historic and brutal September heat wave, one that has already rewritten the climate records of both Canada and the United States. Temperatures are soaring to levels never before recorded in autumn, with all-time fall records collapsing day after day.

In the United States Pacific Northwest, the heat has been extraordinary. Spokane, Washington officially reached 99°F (37.2°C), while downtown observations climbed even higher to 101°F (38.3°C). Deer Park, Washington also reported 101°F, making this the hottest fall day in the region’s history. For early September, these temperatures are beyond unprecedented, more typical of the desert Southwest in midsummer than of inland Washington in September.

Across the border, the Canadian side of this heat wave is nothing short of historic. At Lillooet, British Columbia, the temperature reached an astonishing 38.6°C (101.5°F), breaking not just September records but establishing one of the hottest autumn days in Canadian climate history. Lytton followed closely with 38.2°C, and Ashcroft set a new record with 37.9°C. Other nearby towns also reported maxima above 37°C, further solidifying this outbreak as a continent-shaping heat event.

This is not an isolated spike but part of a multi-day heat dome that continues to intensify. With records falling since the first day of the outbreak, forecasts now indicate that Canada may set a new national record for the hottest autumn day ever recorded. Such an event underscores the extraordinary persistence and severity of this late-season heat wave, which is both rewriting meteorological history and posing serious risks to health, agriculture, and infrastructure.

The context of these extremes makes them even more shocking. In early September, average highs in interior British Columbia would normally be closer to 20–25°C, with crisp autumn nights signaling the seasonal transition. Instead, towns like Lillooet and Lytton are experiencing mid-summer desert heat in September, with daytime values exceeding 100°F (38°C). For many Canadian stations, these values rank not only as September records but as among the highest temperatures ever recorded outside of July or August.

In summary, the September 2025 Western Heat Wave stands as one of the most astonishing climate events in Canadian and U.S. history. With 38.6°C in Lillooet, 38.2°C in Lytton, and 37.9°C in Ashcroft, combined with 101°F in Spokane and Deer Park, the event has already secured its place in meteorological records. With forecasts pointing to even higher values tomorrow, Canada is poised to register its hottest autumn day on record, making this heat wave a truly historic moment in North American climate history.

Illustration picture: https://www.torontosom.ca/blog/places-to-visit-in-canada-during-the-fall-season