Historical Analysis of Pacific Northwest Heat Waves

A retrospective study of heat waves in a region of the Pacific Northwest (specifically, west of the Cascade Mountains in WA and OR) has been ongoing. A variety of ways to define heat events were tested due to the lack of a regional definition; we focus here on results based on heat events defined as three consecutive days above the 99th percentile for either the maximum or minimum temperatures separately. The synoptic characteristics of the maximum temperature and minimum temperature defined heat events indicate differences between the two types of events. An event that occurred in the region in 2009 was particularly extreme in terms of the duration of the minimum temperatures over the 99th percentile threshold and the all-time record maximum temperatures broken in many locations, and that event is put into perspective upon examining the rest of the historical record. Current literature suggests that the frequency and duration of heat waves is expected to increase in much of the US. Trends in our region are also explored indicating a significant increasing trend in the minimum temperatures but not in the maximum temperatures. Finally, a potential link between our heat events and mortality is examined.