19-20

GNFAC Avalanche Forecast for Fri Feb 14, 2020

Snowpack and Avalanche Discussion

<p>Strong winds and plenty of soft snow available for transport have created fresh wind drifts. These drifts can break several feet deep with the weight of a skier or rider today. Watch out for these drifts near ridgelines, in cross-loaded gullies, and downwind of tree islands. Steer clear of these drifts to avoid getting surprised by a slide. If you feel the snow stiffening under your feet or see cracks shooting out in front of your skis/sled, you’ve found one of these potentially dangerous drifts. Stop. Reevaluate. And then move to a less wind affected slope.</p>

<p>Larger, deeper avalanches also remain possible on weak layers near the ground. Yesterday, a snowmobiler triggered a slide on a small slope near Buck Ridge completely burying his snowmobile while he luckily stayed on top (<strong><a href="https://www.mtavalanche.com/images/20/mcatee-snowmobile-triggered-slide…;). The debris piled up 12-15 ft deep in a creek drainage. On Wednesday, skiers on Garnet Mountain triggered two avalanches that broke up to 4 ft deep on the weak, faceted, snow at the ground (<strong><a href="https://www.mtavalanche.com/images/20/remotely-triggered-slide-garnet">…;). These slides were triggered from a thin area 15 ft away on slightly lower angled terrain.</p>

<p>Over the last two days I covered a lot of ground riding near Cooke City and only saw evidence of one avalanche that broke last weekend (<strong><a href="https://www.youtube.com/watch?v=_u7O2cXLAGw&amp;list=PLXu5151nmAvSbcbVf…;). This fits with reports we’ve gotten from around the region (there have only been a few slides reported since last Sunday) and makes me cautiously optimistic about the snowpack. As we get further out from the last storm, it’s becoming less likely that you’ll trigger a deeper avalanche. However, the handful of recent slides demonstrate that the possibility is still out there.</p>

<p>Good travel practices remain key: always ride with a partner, only expose one person at a time to steep slopes, and always carry rescue gear (beacon, shovel, and probe). Tilt the odds in your favor by avoiding freshly windloaded slopes and staying away from thin areas that are likely triggering spots.</p>

<p>The avalanche danger is MODERATE today across our forecast area.</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

Snowmobile Triggered Slide in McAtee Basin

Buck Ridge
Northern Madison
Code
SS-AMu-R2-D1.5-O
Latitude
45.18340
Longitude
-111.44000
Notes

From observation: "My riding group came upon a group of three riders from out of state digging out a sled. A single rider had been side hilling a steep slope above a deep creek drainage. This is where the trail leaves Third Yellow mule and drops into McAtee. The slope broke with a single rider high on the slope completely burying the sled. The rider managed to stay on top of the debris. The debris was very deep (~12'-15') as it filled in the drainage below."

Number of slides
1
Number caught
1
Number buried
0
Avalanche Type
Soft slab avalanche
Trigger
Snowmobile
Trigger Modifier
u-An unintentional release
R size
2
D size
1.5
Bed Surface
O - Old snow
Vertical Fall
40ft
Slab Width
50.00ft
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Single Avalanche
Advisory Year

From observation: "My riding group came upon a group of three riders from out of state digging out a sled. A single rider had been side hilling a steep slope above a deep creek drainage. This is where the trail leaves Third Yellow mule and drops into McAtee. The slope broke with a single rider high on the slope completely burying the sled. The rider managed to stay on top of the debris. The debris was very deep (~12'-15') as it filled in the drainage below."

Photo: R. Smith

Northern Madison, 2020-02-14

Remotely triggered avalanches on Garnet Mtn.

Garnet Mtn.
Northern Gallatin
Code
HS-ASr-R1-D1-O
Elevation
8000
Aspect
NW
Latitude
45.42400
Longitude
-111.20500
Notes

Two avalanches simultaneously remotely triggered by skiers on Wednesday, 2/12/2020. 

From email: "NW aspect at 8000 ft on Garnet Mountain. Two slides, one 15 feet across and one 10 feet across, remotely triggered from 15 ft away. Crown was about four feet deep, triggered on the facets. Didn't travel more than 30 vertical feet.  One slide triggered in dense trees, and both slides traveled into densely treed areas. The snowpack was relatively shallow in the area where slide was triggered. Signs of instability were noted (Back on low angle terrain, after triggering the above slide), Cracks that propagated out 10+feet and were very deep and whomphing."

Number of slides
2
Number caught
0
Number buried
0
Avalanche Type
Hard slab avalanche
Trigger
Skier
Trigger Modifier
r-A remote avalanche released by the indicated trigger
R size
1
D size
1
Bed Surface
O - Old snow
Problem Type
Persistent Weak Layer
Slab Thickness
48.0 inches
Vertical Fall
30ft
Slab Width
30.00ft
Weak Layer Grain type
Faceted Crystals
Slab Thickness units
inches
Single / Multiple / Red Flag
Multiple Avalanches
Advisory Year

GNFAC Avalanche Forecast for Thu Feb 13, 2020

Snowpack and Avalanche Discussion

<p>Throughout our forecast area the snowpack is trending towards stability. Snowfall in the last day was measured at 2.5% density which is another way of saying it is 97.5% air…almost weightless. Light wind is not loading slopes and Sunday was the last significant avalanche. <em>Yesterday’s reporting of the avalanche on Saddle Peak was incorrect; it was an old avalanche, not a new one.</em></p>

<p>As expected, most avalanches ran during and immediately after the storm with the northern mountains, especially the Bridger Range, seeing the most action. The carnage is well documented in our <u><strong><a href="https://www.mtavalanche.com/photos">Photos</a></strong></u&gt; page, <u><strong><a href="https://www.mtavalanche.com/avalanche-activity">Avalanche Activity</a></strong></u> page and also listed on our <u><strong><a href="https://www.mtavalanche.com/weather/wx-avalanche-log">Weather and Avalanche Log</a></strong></u>. Since then we’ve been in the field gathering information on the post-storm stability of the snowpack.</p>

<p>Yesterday, Ian went to Cooke City and Dave visited the <u><a href="https://www.mtavalanche.com/node/13952">Throne</a></u&gt; in the Bridger Range. Ian found one large slide on <u><a href="https://www.mtavalanche.com/node/21674">Wolverine Peak</a></u> that broke in the storm snow and cautioned that although conditions are improving, in the immediate future slides are still possible (<u><strong><a href="https://youtu.be/_u7O2cXLAGw">video</a></strong></u&gt;). Dave had a similar message in his <u><strong><a href="https://youtu.be/EjxZrP2OLG0">video</a></strong></u&gt; since he found a very deep snowpack and could not get breaks in his stability tests, a positive, but muted sign, since he was surrounded by avalanches that broke over the weekend. I visited Mt Ellis on Tuesday (<u><strong><a href="https://youtu.be/vr00k3PgY_E">video</a></strong></u&gt;), Taylor Fork and Cabin Creek on Monday (<u><strong><a href="https://youtu.be/1kW1KxfjQK8">video</a></strong></u&gt;) and Lionhead on Sunday (<u><strong><a href="https://youtu.be/vOKh3V6ZDJ0">video</a></strong></u&gt;). All 5 field trips had a similar message: the snowpack has mostly adjusted to the 3-5 feet of snow, yet sugary facets at the ground are occasionally breaking in our stability tests and remain the primary concern. On many slopes this layer already avalanched, but not on all. The chances of triggering avalanches is decreasing, yet not out of the question. That’s why I’m using words like “mostly”, “possible” and “trending” to describe the current state of affairs.</p>

<p>For today, the avalanche danger throughout our forecast area is rated MODERATE.</p>

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