Mono winds

Mono winds are strong, dry downslope winds that occur along the western slopes of the central Sierra Nevada in California. They are a type of foehn wind that typically blow from the northeast, descending the Sierra into the foothills. Wind speeds in Mono wind events regularly exceed 50 mph (80 km/h), with gusts recorded over 100 mph (160 km/h). The name "Mono" derives from Mono Lake and the indigenous Mono people. Mono winds are part of the broader family of California's offshore wind systems, like the Santa Ana winds in Southern California and Diablo winds in the Bay Area.^[1]

Mono winds form when high-pressure systems develop over the Great Basin following the passage of cold fronts. The cold, dense air flows westward, pushed by the pressure gradient, and descends the Sierra Nevada, accelerating as it moves downhill and warming adiabatically. These conditions occur primarily between October and April.^[2]

In some cases, strong upper-level winds in the jet stream enhance these effects, transporting momentum downward and increasing surface wind speeds. This type of Mono wind, often referred to as "Type II," can generate turbulent rotors and mountain waves, making the winds especially destructive and unpredictable.^[3]

Mono winds are most common in the central Sierra Nevada, especially in and around Yosemite National Park. They affect communities in Mariposa, Madera, and Tuolumne counties. Topographic features like canyons and passes focus and intensify wind speeds, making some areas more vulnerable than others.^[1]

While similar downslope winds occur elsewhere in California, the term "Mono winds" specifically refers to those impacting the Sierra region west of Mono Lake. These events are analogous to Santa Ana and Diablo winds, with regional differences in temperature and geography.^{[citation needed]}

Mono winds have historically caused significant damage to forests, infrastructure, and homes. Their gusty nature often results in widespread treefall, particularly among conifer forests.^[4] In January 2021, a severe wind event toppled hundreds of trees in Yosemite, including at least 15 giant sequoias in the Mariposa Grove, damaging park infrastructure and forcing a closure of almost two weeks^[5]

Mono winds create dangerous fire weather conditions due to their speed and extremely low humidity. They can rapidly spread existing fires and trigger new ignitions through downed power lines. For instance, the Mountain View Fire in Mono County destroyed over 90 homes after wind gusts drove the fire through the community of Walker in November 2020.^[6]

The terrain-induced turbulence from Mono winds can pose serious hazards to aviation. Mountain waves and rotor winds generated during these events are capable of producing severe turbulence and sudden wind shear, particularly dangerous to small aircraft and firefighting operations.^[1]

• December 12, 1967: A destructive Mono wind event caused widespread damage in Bass Lake and North Fork, California. Estimated gusts over 70 mph toppled trees and downed power lines, resulting in more than $1 million in property damage (in 1967 dollars).^[2]
• December 7, 1971: Strong Mono winds swept through Yosemite National Park, blowing down over 200 trees. The Badger Pass Ski Area suffered major damage when high winds wrecked the chairlift infrastructure.
• November 17–18, 2020: The Mountain View Fire ignited near Walker, California, during a severe Mono wind event. Gusty conditions rapidly spread the fire, destroying approximately 90 homes and killing one resident. The fire burned over 28,000 acres before containment.^[6]
• January 19, 2021: One of the most destructive Mono wind events in recent history impacted the central Sierra Nevada. Yosemite National Park was hit especially hard, with hundreds of trees downed, including at least 15 giant sequoias in the Mariposa Grove.^[7] The park was closed for nearly two weeks due to extensive damage and safety concerns.^[5]