19-20

GNFAC Avalanche Forecast for Fri Feb 21, 2020

Snowpack and Avalanche Discussion

<p> Without new snow to load them the weak layers that have been hanging out at the bottom of our snowpack all year are slowly gaining strength. However, recent large natural avalanches are a good reminder that slides on these weak layers are still possible if you find just the wrong spot. Yesterday, Alex looked at slides near Flathead Pass in the Bridger Range that broke 3-5’ deep and hundreds of feet wide earlier this week <a> (</a><a href="https://www.mtavalanche.com/images/20/naturals-north-flathead-pass"><st…;, <a href="https://www.mtavalanche.com/images/20/natural-avalanche-near-flathead-p…;). Large avalanches also broke 3-4 days ago on the heavily wind loaded south face of Wilson Peak near Big Sky (<a href="https://www.mtavalanche.com/images/20/natural-avalanches-wilson"><stron…;). Unfortunately, we don’t have great tools to test weak layers at bottom of a deep snowpack. But we know the weak layer is there and has avalanched recently. Continuing to be conservative in your terrain selection is the best management strategy. Particularly avoid thin, rocky areas which are the most likely trigger points.</p>

<p>Yesterday, loose wet avalanches were seen on steep rocky slopes in the Bridger Range and near Cooke City. Wet point releases can start at your feet or come down from rocky slopes above you. Be especially mindful on higher consequence slopes where a small slide could push you over a cliff or into a gully. One of these wet loose slides triggered a thin slab avalanche on wind drifted snow north of Bridger Bowl (<a href="https://www.mtavalanche.com/images/20/wet-snow-triggered-wind-slab"><st…;). This particular slab was thin but debris from a wet loose avalanche could also trigger a slide on the weak layers at the ground. Watch for roller balls and pinwheels as the day heats up and move to shadier or lower angled slopes once they start (<a href="https://www.mtavalanche.com/images/20/roller-balls">photo</a&gt;).</p>

<p>With this combination of concerns, the avalanche danger is MODERATE today.</p>

<p>The snowpack is generally stable in the mountains around West Yellowstone. We’re a week out from the last reported avalanche (<strong><a href="https://www.mtavalanche.com/node/22074">details</a></strong&gt;). The weak snow at the ground is still there, but triggering an avalanche on it is unlikely (<strong><a href="https://www.youtube.com/watch?v=2IzNvRo0R3w&amp;list=PLXu5151nmAvSbcbVf…;). Watch out for the possibility of trigging small wet loose avalanches as the surface snow becomes wet with today’s warm temperatures and sunny skies.</p>

<p>Large avalanches are unlikely and the avalanche danger is LOW.</p>

<p>If you get out, please send us your observations no matter how brief. You can fill out an&nbsp;<strong><a href="https://mtavalanche.us17.list-manage.com/track/click?u=6653a830e4819c9e…; target="_blank">observation form</a></strong>, email us (<strong><a href="mailto:mtavalanche@gmail.com&quot; target="_blank">mtavalanche@gmail.com</a></strong>), leave a VM at 406-587-6984, or Instagram (#gnfacobs).</p>

Upcoming Avalanche Education and Events

Our education calendar is full of awareness lectures and field courses. Check it out and plan to attend one or two: Events and Education Calendar.

COOKE CITY

Every Friday and Saturday, Snowpack Update and Rescue Training. Friday, 6:30-7:30 p.m. at the Soda Butte Lodge. Saturday anytime between 10-2 @ Round Lake.

BOZEMAN

Skier triggered thin slab in Bridgers

Texas Meadow
Bridger Range
Code
SS-AS-R1-D1
Latitude
45.84060
Longitude
-110.93300
Notes

From email on 2/20/2020: "I found some localized instabilities, including some wind whales on the ridge north of Bradley’s... The slide in the photo probably happened naturally this late morning, with a trigger of sun-heated snow from the cliffs above (just west of Texas Hill). It ran approximately 100 meters.

From e-mail on 2/21/2020" "I was a few hundred feet north of it when it released. It was skier-triggered by another party traversing high on that slope. It carried the skier for most of the slide path."

Number of slides
1
Number caught
1
Number buried
0
Number killed
0
Avalanche Type
Soft slab avalanche
Trigger
Skier
R size
1
D size
1
Slab Thickness
6.0 inches
Vertical Fall
300ft
Slab Width
10.00ft
Slab Thickness units
inches
Single / Multiple / Red Flag
Single Avalanche
Advisory Year

From email on 2/20/2020: "I found some localized instabilities, including some wind whales on the ridge north of Bradley’s... The slide in the photo probably happened naturally this late morning, with a trigger of sun-heated snow from the cliffs above (just west of Texas Hill). It ran approximately 100 meters."

Photo: T. Allen

Bridger Range, 2020-02-21