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The Pacific Northwest heat wave of 25-30 June 2021: Synoptic/mesoscale conditions and climate perspective

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Author(s): Clifford Mass, David Ovens, John Christy, Robert Conrick

Document Type:
Publisher: Weather and Forecasting
Published Year: 2024
Volume: 39
Number: 2
Pages: 275 to 291
DOI Identifier: 10.1175/WAF-D-23-0154.1
ISBN Identifier:
Keywords: Mesoscale processes Extreme events Synoptic-scale processes Mesoscale processes Mesoscale systems Mesoscale forecasting

An unprecedented heat wave occurred over the Pacific Northwest and southwest Canada on 25–30 June 2021, resulting in all-time temperature records that greatly exceeded previous record maximum temperatures. The impacts were substantial, including several hundred deaths, thousands of hospitalizations, a major wildfire in Lytton, British Columbia, Canada, and severe damage to regional vegetation. Several factors came together to produce this extreme event: a record-breaking midtropospheric ridge over British Columbia in the optimal location, record-breaking midtropospheric temperatures, strong subsidence in the lower atmosphere, low-level easterly flow that produced downslope warming on regional terrain and the removal of cooler marine air, an approaching low-level trough that enhanced downslope flow, the occurrence at a time of maximum insolation, and drier-than-normal soil moisture. It is shown that all-time-record temperatures have not become more frequent and that annual high temperatures only increased at the rate of baseline global warming. Although anthropogenic warming may have contributed as much as 1°C to the event, there is little evidence of further amplification from increasing greenhouse gases. Weather forecasts were excellent for this event, with highly accurate predictions of the extreme temperatures.

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Suggested Citations:
In Text Citation:
Mass and others (2024) or (Mass et al., 2024)

References Citation:
Mass, C., D. Ovens, J. Christy, and R. Conrick, 2024, The Pacific Northwest heat wave of 25-30 June 2021: Synoptic/mesoscale conditions and climate perspective: Weather and Forecasting, Vol. 39, No. 2, pp. 275-291, doi: 10.1175/WAF-D-23-0154.1.