Earth, Wind, and Fire: Are Boulder’s Extreme Downslope Winds Changing?

Abstract A Denver newspaper in 2016 reported that a new Colorado all-time record peak wind gust of 148 mph was recorded on 18 February 2016, on Monarch Pass in the Colorado Rockies near 11 000 ft above sea level. The article stated that this broke the previous record of 147 mph set on 25 January 1971 at the National Science Foundation (NSF) National Center for Atmospheric Research (NCAR) Mesa Laboratory, at an altitude of 6077 ft, on the western edge of Boulder, Colorado. Though there is no actual official peak gust record in Colorado, this raised the issue that Boulder had not recently experienced winds of the magnitude of the megadownslope windstorms that wracked the area in the 1960s, 1970s, and 1980s when extreme wind gusts recorded at the NSF NCAR Mesa Laboratory were not unusual. Due to Boulder’s location at the eastern foot of a north–south mountain range ( Earth ), it is susceptible to destructive downslope winds ( wind ) often accompanied by fires ( fire ) such as the downslope wind-driven Marshall Fire just east of Boulder on 30 December 2021 that destroyed nearly 1100 homes. But after the 1990s, the weather station anemometer at NSF NCAR did not record a peak gust much over 100 mph. What changed? This detective story describes the search for causes of the apparent decrease in strength of extreme windstorms at NSF NCAR and their impacts in the Boulder area. The suspects in Boulder include a change in instrument location, changes in building codes, and increasing roughness length from tree growth. But climate change emerges as a chief culprit. Significance Statement National Science Foundation (NSF) National Center for Atmospheric Research (NCAR) was at the epicenter of megadownslope windstorms that wracked Boulder in the 1960s, 1970s, and 1980s when extreme windstorms were not unusual. But after the 1990s, the weather station anemometer at NSF NCAR, which replaced the previous anemometer that recorded the huge gusts, did not record a peak gust much over 100 mph. What changed? This detective story describes the search for causes of the apparent decrease in strength of extreme winds at NSF NCAR and their impacts in the Boulder area. Changing instrument location is part of the story, but climate change emerges as a key culprit.