New Study Lays Out Hidden Backstory Behind Deadly Pacific Northwest Heatwave

An anonymous reader quotes a report from Phys.Org: Last summer, a deadly wave of heat struck the Pacific Northwest, causing temperatures to soar more than 30 degrees Fahrenheit above normal and killing more than a thousand people. A new study has uncovered the sequence of events that precipitated the disaster, providing information that could further our understanding of heat formation on the North American continent. By reviewing large-scale weather conditions and formations before the heat wave, University of Chicago scientists discovered that a cyclone spawned an "anticyclone," which combined to produce and then trap heat near the surface of the region. [...] Using data collected from satellites and on the ground, UChicago scientists set out to re-create the sequence of events. They found that in the week prior, a cyclone had formed over the Gulf of Alaska. Cyclones are large, spiral-shaped systems that form around a center of low pressure. (Think of the spiral clouds you see during hurricanes.) When clouds form out of water vapor, the process actually releases heat, which accumulated in the atmosphere. Then, as the cyclone moved slowly away, it triggered the formation of an anticyclone to the east -- a system that rotates slowly around a center of high pressure instead of low. These are known as "blocking" systems because they disrupt the normal eastward movement of weather systems. A blocking anticyclone acts like a blanket, trapping heat in a region. The result was a warm, stagnant column of air that made it difficult for surface heat to escape to the upper atmosphere as it normally does. The study has been published in the journal Geophysical Research Letters.

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