An unprecedented weather system that caused the devastating Labor Day wildfires in 2020 also resulted in historically low temperatures and early snowfall in parts of the Rocky Mountains. A recent study conducted by Portland State University provides new insights into the meteorological factors that contributed to this extreme weather event and its far-reaching consequences.
A high-pressure ridge was responsible for the unusually warm weather leading up to the event. According to Russell, the primary atmospheric driver was an exceptionally strong wave pattern, the most intense on record for that time of year, which persisted for several days. This wave pattern broke, similar to an ocean wave, triggering a powerful wind event over western Oregon.
“Even during winter, this would have been a remarkably strong wind event, but for early September, there’s no precedent for such intensity in the observational record,” explained Paul Loikith, an associate professor of geography and director of PSU’s Climate Science Lab.
The combination of warm temperatures and strong, dry easterly winds fueled numerous large wildfires, resulting in the evacuation of over 40,000 individuals, the destruction of 5,000 homes and businesses, and the loss of nine lives in Oregon. The widespread wildfire smoke also caused abnormally high levels of air pollution across the region for the subsequent two weeks. An analysis of air parcel backward trajectories revealed that the dry air over the Pacific Northwest, which exacerbated the fire danger, originated in western Canada at altitudes exceeding 5,000 meters.
“The air at these high altitudes is extremely dry, and as it descends to the surface, it warms up, further exacerbating the dryness,” Russell explained. “This helps to clarify the source of the dry air.”
2024-03-02 10:00:04
Source from phys.org