Record-Breaking Heat Wave Scorches the Pacific Northwest

[As written for Lamb Weston quarterly newsletter]


A significant heat wave has scorched the Pacific Northwest from Friday June 25 through Thursday July 1, 2021, with dozens of daily, monthly, and all-time temperature records broken. High temperatures for several days reached 100-120 degrees across Washington, Oregon, Idaho, and into Canada.


The Science

The primary factor that contributed to the historical heat wave in the Pacific Northwest was a “heat dome”. A heat dome is a large, highly anomalous area of upper-level high pressure that traps in hot air. Under a heat dome, air is sinking toward the surface, and compresses as it falls resulting in even further warming. This creates significantly above normal temperatures at the surface which can rival some of the hottest places in the world. Some experts have called this event a “once in a millennium”, as the magnitude of the heat is 4-5 standard deviations above normal.

Additionally, a small upper-level low was also in place just off the coast. Winds naturally flow from areas of high pressure to areas of low pressure, as the atmosphere attempts to achieve equilibrium. Therefore, winds blew from areas of high elevation west to areas of lower elevation east, called downsloping, which results in additional compressional warming of the air.




The Records

Widespread excessive Heat Warnings were issued across Washington, Oregon, Idaho, western Montana, northern California, and western Nevada. Temperatures climbed to 30°F to 50°F degrees above normal for nearly a week.

Dozens of daily, monthly, and even all-time high temperature records were broken including a few state and national records. Some of the most notable records are listed below:


- Portland, Oregon set an all-time high temperature record of 115°F (previously 107°F in 1981)

- Salem, Oregon set an all-time high temperature record of 117°F (previously 108°F in 1927, 1941, and 1981)

- Dallas, Oregon set an all-time high temperature record of 115°F (previously 111°F in 1992 and 1998)

- Hermiston, Oregon set an all-time high temperature record of 118°F, which is preliminarily the new state record

- Seattle, Washington set an all-time high temperature record of 108°F (previously 103°F in 2009) and had its first back-to-back 100+°F days ever.

- Dallesport, Washington set an all-time high temperature record of 118°F, which is preliminarily the new state record (previously 111°F in 1992 and 1998)

- Coeur D’Alene, Idaho set an all-time high temperature record of 109°F (previously 102°F in 2008)

- Lytton, Canada broke the nation’s all-time high temperature record of 113°F when it hit 116°F Sunday, 118°F Monday, and 121°F Tuesday, which ties Death Valley for the day’s highest temperatures in North America


*Previous record dates are prior to this event period




The Impacts

Heat waves of this magnitude and longevity pose a serious risk to humans, agriculture, and the environment. While hurricanes, tornado outbreaks, and major winter storms seem to steal the spotlight when it comes to significant weather events, heat-related illness is the number one weather-related cause of death in the United States. Between Friday June 25 and Wednesday June 30, 2021, at least 63 deaths occurred in the United States that were directly attributed to the heat wave, as well as a staggering 486 deaths in Canada. Not only are daytime temperatures well above normal, but nighttime temperatures are also remaining well above normal. This puts the homeless and those without air conditioners at an exceptional risk for heat-related illness, and only roughly 40-50% of homes in the Pacific Northwest region have air conditioners due to the rarity of extreme heat.

The widespread drought conditions already in place across the Pacific Northwest are aiding in the dry pattern and hot temperatures as well, and drought conditions will continue to worsen due to the excessive heat. The heat is not only pulling all available moisture from the soils, but it is also evaporating snowmelt from the sides of mountains, robbing lower elevations of usual water supplies. The Pacific Northwest drought is contributing to deteriorating agricultural conditions across the United States, with the following production areas experiencing drought conditions as of June 30, 2021:


- Corn: 41%

- Soybeans: 36%

- Spring Wheat: 89%

- Winter Wheat: 25%

- Durum Wheat: 90%

- Hay: 37%

- Alfalfa: 65%

- Cattle: 38%



The western United States has had a very hot and dry spring and early start to summer, prompting a wildfire season that is off to an aggressive start. With extremely dry vegetation and soils, and very limited runoff from snowmelt, we are likely to see a historic wildfire season. One concern that has been outlined by firefighters and first responders is the lack of available water in lakes to put out large fires. Year-to-date, 2021 has been the most active wildfire year since 2011.



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