Three western pacific typhoons strengthened fire weather in the recent
conflagration in northwest U.S.
Abstract
A heatwave and fire outbreak in the western United States in early
September of 2020 resulted from an atmospheric wave train that spanned
the Pacific Ocean basin. Days before the atmospheric waves developed in
the U.S., three western Pacific tropical cyclones underwent an
extratropical transition within an unprecedentedly short span of 12
days. Using a climate diagnostic approach and historical forecast data
from the Global Ensemble Forecast System (GEFS), it was found that the
amplitude of the atmospheric waves accompanying the western U.S. fire
weather would have been reduced if not for the influence of these
cyclones. Together, the recurving typhoons provided a significant source
of Rossby wave activity toward North America-amplifying the ridge over
the U.S. west coast while deepening the trough in central Canada. This
anomalous circulation was a precursor to the severe frontal system that
caused extreme winds in western Oregon-starting and rapidly spreading
fire.