Yosemite National Park is now Closed to general public until January 26th for clean up.

Sierra Rec Magazine – January 21, 2021 – On January 19, 2021 the Sierra was under weather warnings for high winds across the Sierra. Ski resorts closed in Lake Tahoe, but no one expected the devastation that would hit the Western Slopes of the Central Sierra. Winds known as the Mono winds struct the Central Sierra with efficiency as it laid trees down from Sequoia National Park to Calaveras State Park in the North. However it was Yosemite National Park that may have taken the worst of this storms blows.

Yosemite National Park arose the next morning to utter destruction in Yosemite Valley & Mariposa regions. Trees toppled onto vehicles, homes, boardwalks and buildings. Teams of people trapped in their current location with limited travel options. The park quickly closed to the public until at least Friday as it surveyed the damage and began clearing roads.

Today Yosemite released another series of images and extended the closure until Tuesday January 26th as the discovered more of the story, including the toppling of the Giant sequoia.


What are Mono Winds?

Mono Winds are a localized wind that blows across the western slopes of the central Sierra Nevada and
into the foothills below from the northeast. The name Mono Winds was given to these winds
because they blew into the central Sierra Nevada from the direction of Mono Lake. The word “Mono”
was derived from a Native American tribe who once resided in the area.
Mono Winds are strong winds that blow downhill across the western slopes of the central Sierra
Nevada from the northeast. In an ideal atmospheric pattern, air moving from the northeast and flows up
and over the high peaks of the Sierra Nevada. As this air rushes several thousand feet downhill, it
increases in speed and also dries out. The rugged topography of the Sierra Nevada also causes the air
to be funneled through tight spaces which further increases its speed. This results in winds that can
reach speeds of 50 mph or more.
Mono Winds form when an area of high pressure sets up over the Great Basin. Air flows in a
clockwise direction around high pressure. In some situations, the air is “squeezed” better than others
because of the differences in pressure in the atmosphere. The more air is squeezed, the faster it
blows. In a typical Mono Wind event, winds reach speeds of at least 50 mph while stronger events can
see winds exceed 100 mph!

The strength of Mono Winds is also determined by the jet stream, which is the band of winds several
thousand feet above the surface of the earth. When the winds in the jet stream are in the same direction
as the winds closer to the surface of the earth they can “mix down” or more easily be transported
towards the ground. This enables the very strong and powerful winds that typically blow well above
the surface of the earth towards the ground.
Jetstream winds are often in excess of 80 to 100 mph at over 20,000 feet in the atmosphere. In ideal
situations, these winds speeds will be felt by you (or anything else) on the ground.

The Dangers of Mono Winds

Mono Winds can easily reach speeds in excess of 50 mph and in extreme cases as high as over 100
mph. Typically Mono Winds are most common between October and April, and especially around
December and January when the cold air that drives them is most common. While the broad area
affected by Mono Winds is along the western slopes of the central Sierra Nevada, they are most
common within Yosemite National Park. However, due to the localized effects of terrain channeling
these winds, they can often affect one area tremendously and barely impact another area just a
few hundred feet away.
The most common danger from Mono Winds is trees falling down. Fallen trees can easily strike
visitors as well as obstruct traveling on roads and make navigating trails difficult. Even campers in
enclosed structures such as cabins can be at risk. If park officials recommend or order evacuations due
to Mono Winds, heed their advice and leave for a safe area. If an area is designated as being closed
due to the risk of fallen trees, please stay out of it until park officials determine is it once again safe to
enter.
In addition to the risk of trees falling down, Mono Winds can also cause other loose objects to be
blown. Even the most secure tent is at risk when wind speeds reach 50 mph or greater. Debris can
easily pierce a tent. Even if you remain in the open, fine particles like dirt will be easily blown which can
put your eyes at risk.
Lastly, there is always a risk for fires to spread when strong winds blow. Remaining in a heavily
wooded area when winds pick up and any sort fire is going on nearby – even a campfire – is a recipe
for disaster. Always, always obey park guidelines on campfires on any day.

Information regarding mono winds provided by NPS “the dangers Of Mono winds”

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