20-21

GNFAC Avalanche Forecast for Thu Feb 11, 2021

Snowpack and Avalanche Discussion

<p>Snowfall stopped Monday afternoon after dropping 3-4’ of snow. As a result there were many avalanches throughout our entire forecast area, many on wind-loaded slopes. Weak, sugary snow at the ground avalanched, a few slopes for the second or third time. Some broke at the interface of the new and old snow. It is our third day after the storm and the snowpack is no longer hair-trigger. However, large avalanches are still possible as the snowpack adjusts to this heavy burden. Our field days to the Bridger Range, Buck Ridge, northern Madison Range and Lionhead all point to slowly strengthening snowpack. Yesterday, in the Bridger Range, Dave noted the new snow <em>more than doubled </em>the total depth. He saw many avalanches and remains concerned about slopes that have not yet slid (<a href="https://youtu.be/MyCLaNW0eUU"><strong><u>video</u></strong></a&gt;). Ian was in Lionhead (<a href="https://youtu.be/Nx0u7cLceuc"><strong><u>video</u></strong></a&gt;) where it only snowed half as much as the northern areas and described the stability as “not bad”, one of the better endorsements all season. Be cautious if you venture into avalanche terrain. Dig and test the snowpack to make sure you are not choosing an unstable slope. Many of the <a href="https://www.avalanche.state.co.us/accidents/us/"><strong><u>16 recent avalanche fatalities</u></strong></a> involved <em>multiple victims</em> per incident, so only expose one person at a time to avalanche terrain. “Ski one at a time” is to be taken literally, not one person skiing every 30 seconds. This way, if an avalanche happens only one may die.&nbsp;</p>

<p>Since triggering avalanches is possible, for today the avalanche danger is rated MODERATE on all slopes.</p>

<p>In the last 5 days we have many new <a href="https://www.youtube.com/playlist?list=PLXu5151nmAvQDzKmH5K3ZS8Gg3DzwsZ3…;, <a href="https://www.mtavalanche.com/photos"><strong><u>pictures</u></strong></a…;, <a href="https://www.mtavalanche.com/avalanche-activity"><strong><u>avalanche details</u></strong></a> and <a href="https://www.mtavalanche.com/snowpits"><strong><u>snowpits</u></strong><…; that are worth scrolling through.</p>

<p>By Tuesday morning Cooke City had 3-4 feet of snow and strong wind at all elevations and many directions. This combination triggered avalanches. Yesterday, a large slide was seen on the south face of Abundance (<a href="https://www.mtavalanche.com/images/21/large-avalanche-mt-abundance"><st…;) breaking about as wide as it could. Also, on Town Hill, a natural avalanche was seen early yesterday morning which broke on the ground (<a href="https://www.mtavalanche.com/images/21/natural-avalanche-town-hill-cooke…;). Wind-loading of the new snow was a common denominator in these slides as well as the <a href="https://www.mtavalanche.com/images/21/bison-triggered-avalanche-lamar-v… triggered slide</u></strong></a> in Lamar Valley (outside our area, but fun to see nonetheless). Our <a href="https://www.mtavalanche.com/photos"><strong><u>photos page</u></strong></a> (filter for Cooke City) shows many slides from the last couple days. Wind-loaded slopes should be approached with caution which are found on most slopes, not only at the ridgelines. For today it is possible to trigger a slide on steep slopes and the danger is rated MODERATE.&nbsp;</p>

<p>If you get out, please send us your observations no matter how brief. You can submit them via our <a href="https://www.mtavalanche.com/node/add/snow_observation"><strong><u>websi…;, email (<a href="mailto:mtavalanche@gmail.com"><strong><u>mtavalanche@gmail.com</u></str…;), phone (406-587-6984), or Instagram (#gnfacobs).</p>

A USFS message: Parking Etiquette

Snowplows are out there working hard to keep roads and trailheads open for YOU. Give them--and your car--some space!

Natural avalanche on Henderson Ridge, Cooke City

Henderson Bench
Cooke City
Code
N-R2-D2
Aspect
NE
Latitude
45.05580
Longitude
-109.94700
Notes

This natural avalanche occurred on a wind loaded, NE aspect above Henderson Bench outside Cooke City. Wind- loading has been the main avalanche concern.

Number of slides
1
Number caught
0
Number buried
0
Trigger
Natural trigger
R size
2
D size
2
Problem Type
Wind-Drifted Snow
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Single Avalanche
Advisory Year

Large natural avalanche on Mt. Abundance, Cooke

Mt. Abundance
Cooke City
Code
HS-N-R4-D3
Elevation
10000
Aspect
SE
Latitude
45.06870
Longitude
-110.01600
Notes

This large avalanche on the SE face of Mt Abundance, north of Cooke City, released naturally in the last 48 hours. In the photo you can see the fingers of windblown snow from strong westerly wind.

Number of slides
1
Number caught
0
Number buried
0
Avalanche Type
Hard slab avalanche
Trigger
Natural trigger
R size
4
D size
3
Problem Type
Persistent Weak Layer
Vertical Fall
1000ft
Slab Width
750.00ft
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Single Avalanche
Advisory Year