Striking heat wave hits the Pacific Northwest and southwestern Canada
Meteorological fall began Monday, but an expanding heat dome has other plans for the Pacific Northwest and the adjacent southwestern Canada. Temperatures are forecast to rise to between 95 and 105 degrees Fahrenheit across a wide swath Tuesday, with similar conditions anticipated through late in the workweek.
Heat alerts are in effect through Thursday for Washington state to the east of the Cascade Mountains, then across northern Idaho into western Montana. Alerts also extend south into northern Oregon. The highest-level risk – an extreme-heat warning – blankets more than 1 million people, including the cities of Yakima in Washington and Pendleton in Oregon.
Heat warnings are also up for portions of British Columbia through at least Thursday, including in Lytton, which last week saw four days in a row of 104 (40 degrees Celsius) or higher, tying a record for the most in any month.
Conditions in Canada could challenge a national record high for September and for this late in the year during this heat wave.
High temperatures, scattered lightning and sunbaked land are also causing a flare in the historic fire season ongoing in Canada. Rejuvenated blazes are sending new rounds of smoke south and east.
A blocked weather pattern is delivering extended heat to a zone underneath a heat dome nosing north from the Desert Southwest into British Columbia. It is stabilized by surrounding dips in the jet stream over the Great Lakes region and the eastern Pacific Ocean.
Most of eastern Washington state will witness several days of major to extreme heat risk. At such levels, heat illness can affect all groups, while other threats extend to infrastructure, according to the National Weather Service. Similar conditions can be expected into southern British Columbia.
Widespread highs in the 90s to about 105 equate to 20 to 30 degrees above normal for early September. Overnight readings in the 60s to 70s offer some relief but are about 10 to 20 degrees above average.
The September record high in Canada of 104 degrees could be challenged. In September 2022, the same region saw readings that were close, when it hit 103 degrees (39.6 Celsius) in Lytton.
A handful of record highs are anticipated to the south of the international border through Thursday, as well. Temperatures are forecast to reach 101 degrees in Yakima and Kennewick, Washington. Record-warm lows will be even more numerous.
It follows a holiday weekend of unseasonably high temperatures, including records around the San Francisco Bay Area into the Central Valley of California.
A number of new fires started in British Columbia over the weekend, a result of widespread lightning across the region. A majority of the more than 150 ongoing fires there were started by lightning. Mainly burning in forest, part of the popular Bugaboo Provincial Park was evacuated Sunday.
Fires stretching from near Canada’s southwest coast to the Northwest Territories and Saskatchewan are also sending new rounds of thick smoke downwind with poor air quality. While focused on Canada, some smoke has made it into the north-central United States and will continue to do so.
Canada recently crossed 20 million acres of land burned this year, second only to the unfathomable 42 million-plus acres scorched in 2023.
To the south of the international border, a handful of large fires are burning, and new starts from lightning were reported in Washington, Idaho, Oregon and California during the weekend and Monday. Red-flag warnings and fire weather watches are in effect for portions of that region.
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What’s ahead
While current heat alerts run through Thursday, other than some relaxation for the weekend, there is no significant change on weather modeling through at least the middle of next week.
This would mean more highs in the 90s to perhaps 100-plus in the same areas currently seeing such temperatures through that time frame.
Thereafter, a cooler and wetter air mass may arrive to offer some relief. Confidence in that is presently low, as these weather patterns tend to be tough to dislodge.