19-20

GNFAC Avalanche Forecast for Wed Apr 1, 2020

Snowpack and Avalanche Discussion

<p>In the last two days, the mountains received 12-18” of new snow with 1.3-1.5” <a href="https://www.mtavalanche.com/taxonomy/term/451">snow water equivalent</a> (SWE) favoring the southern ranges. The mountains near West Yellowstone and Cooke City received nearly&nbsp;two feet of snow with 2” SWE. Strong gusts of wind built drifts of snow where human triggered avalanches are likely today. Recent avalanche activity and shooting cracks can indicate this instability. On many slopes, the new snow is adding stress to a weak layer buried 2-3’ deep. The weak layer has presented as a melt-freeze crust, feathery surface hoar crystals, and near-surface facets. We have found it on many slopes (but not all) and received reports of people triggering avalanches on this layer across our advisory area (<a href="https://www.mtavalanche.com/avalanche-activity"><strong>avalanche activity,</strong></a> <a href="https://www.youtube.com/watch?v=ZkyjbN1sWl0&amp;list=PLXu5151nmAvSbcbVf… and Taylor Fork video</strong></a><strong>, </strong><a href="https://www.youtube.com/watch?v=l6eItO1yerM&amp;list=PLXu5151nmAvSbcbVf… Ridge video</strong></a>). Choose to assess for this layer with a snowpit and stability test or choose to stay out of avalanche terrain.</p>

<p>Dangerous avalanche conditions exist today and human triggered avalanches are likely. Plan conservatively to minimize your time in and exposed to avalanche terrain and carefully assess the snowpack and route choices. The avalanche danger is CONSIDERABLE.</p>

<p>In the last two days, the Bridger Range received 13” of snow with 1.2” SWE with light 5-10 mph winds from the west. Small drifts exist near ridgelines and in isolated areas (<a href="https://www.mtavalanche.com/images/20/natural-small-slab-large-cornices…;)</strong> and are dangerous in technical terrain where they can push you into obstacles and cause trauma. Today, avalanches within the new snow and on weak layers buried 1-3 feet under the snow are the primary concern (<strong><a href="https://www.youtube.com/watch?v=S_hEBqY67-g&amp;list=PLXu5151nmAvSbcbVf… video</a></strong>). Cool temperatures and clouds will minimize the wet snow danger today. However, do not underestimate how quickly stability can deteriorate if the sun pokes out this afternoon and the snow surface gets wet.</p>

<p>Human triggered avalanches are possible today. Use careful snowpack assessment and conservative terrain choices to minimize your exposure and respect the state’s stay-at-home directive by opting for mellow objectives close to home. The avalanche danger is MODERATE.</p>

<p>We plan to end daily avalanche forecasts on Sunday, April 5<sup>th</sup> and continue with general bulletins every Monday and Friday through April. We have taken down most weather stations and will no longer receive observations from guides and ski patrol. We need help gathering field data. Please send us your observations no matter how brief. You can fill out an <a href="https://mtavalanche.us17.list-manage.com/track/click?u=6653a830e4819c9e…; target="_blank">observation form</a>, email us (<a href="mailto:mtavalanche@gmail.com&quot; target="_blank">mtavalanche@gmail.com</a>), leave a VM at 406-587-6984, or Instagram (#gnfacobs).</p>

Backcountry Skiing and Stay-at-home Order

A Stay at Home order is in effect for the State of Montana due to COVID-19. This order specifically discourages “outdoor recreation activities that pose enhanced risks of injury or could otherwise stress the ability of local first responders to address the COVID-19 emergency (e.g., backcountry skiing in a manner inconsistent with avalanche recommendations or in closed terrain)”.

Natural small slab and many wet loose in Bridgers

Bridger Peak
Bridger Range
Code
SS-N-R1-D1.5
Elevation
8600
Aspect
E
Latitude
45.77010
Longitude
-110.94000
Notes

GNFAC forecaster observed this 8-12" slab on 3/30/20. Appears to have been triggered by cornice fall today. Also observed several small wet loose slides from previous day and this morning.

Number caught
0
Number buried
0
Avalanche Type
Soft slab avalanche
Trigger
Natural trigger
R size
1
D size
1.5
Problem Type
Wind-Drifted Snow
Slab Thickness
12.0 inches
Vertical Fall
900ft
Slab Width
30.00ft
Slab Thickness units
inches
Single / Multiple / Red Flag
Multiple Avalanches
Advisory Year

Natural avalanche near Cedar Mtn.

Cedar Mtn.
Northern Madison
Code
SS-N-R3-D2-O
Latitude
45.22680
Longitude
-111.51200
Notes

Broke on Surface hoar 1-2 feet deep. Observed 3/30/20 by GNFAC forecasters.

Number of slides
1
Number caught
0
Number buried
0
Avalanche Type
Soft slab avalanche
Trigger
Natural trigger
R size
3
D size
2
Bed Surface
O - Old snow
Problem Type
Persistent Weak Layer
Slab Thickness
18.0 inches
Vertical Fall
200ft
Slab Width
120.00ft
Slab Layer Grain Type
Surface Hoar
Slab Thickness units
inches
Single / Multiple / Red Flag
Single Avalanche
Advisory Year

GNFAC Avalanche Forecast for Tue Mar 31, 2020

Snowpack and Avalanche Discussion

<p>The storm has favored the mountains near West Yellowstone and Cooke City with 5-8” of snow equal to 0.5-1.0” of snow water equivalent (SWE). Strong southwest wind last night drifted snow into fresh slabs. Moderate wind and more snow today will grow larger slabs. Today, fresh wind slabs and avalanches in the new snow are easy to trigger, and natural avalanches are possible. Avalanches can also break deeper on weak layers 1-2 feet down (<a href="https://www.youtube.com/watch?v=ZkyjbN1sWl0&amp;list=PLXu5151nmAvSbcbVf…;

<p>Assume the new snow is unstable and plan your route accordingly, to avoid avalanche terrain. Danger will increase through the day. Make conservative decisions and travel cautiously. Avalanche danger is rated CONSIDERABLE.</p>

<p>The mountains near Bozeman and Big Sky have 2-3” of new snow equal to 0.2-0.4” of SWE. Today more snow and moderate southwest wind will create fresh drifts that can be triggered by a person. Be extra cautious and avoid wind loaded slopes. Wind slabs will be large enough to bury a person or can push you into hazards like trees, rocks or over cliffs (<a href="https://www.mtavalanche.com/images/20/natural-cornice-triggered-avalanc…;, <strong><a href="https://www.mtavalanche.com/images/20/natural-small-slab-large-cornices…;).</p>

<p>Over the last week several slides broke on weak layers 1-2 feet deep (<a href="https://www.mtavalanche.com/images/20/skier-triggered-slide-hyalite"><s…;, </strong><a href="https://www.mtavalanche.com/images/20/two-natural-avalanches-beehive-ba…;, </strong><a href="https://www.mtavalanche.com/weather/wx-avalanche-log"><strong>weather and avalanche log</strong></a>). Yesterday Dave and Doug went to Buck Ridge and saw avalanches that broke 1-2 feet deep on surface hoar (<strong><a href="https://www.youtube.com/watch?v=l6eItO1yerM&amp;list=PLXu5151nmAvSbcbVf…;, <strong><a href="https://www.mtavalanche.com/images/20/small-natural-avalanche-cedar-mtn…;). Similar slides are possible to trigger today.</p>

<p>Expect stability to decrease through the day with more snow and wind, and plan accordingly. Carefully evaluate the snowpack and make conservative choices. Avalanches are possible to trigger and avalanche danger is MODERATE.</p>

<p>We plan to end daily avalanche forecasts on Sunday, April 5<sup>th</sup> and continue with general bulletins every Monday and Friday through April. We have taken down most weather stations and will no longer receive observations from guides and ski patrol. We need help gathering field data. Please send us your observations no matter how brief. You can fill out an <a href="https://mtavalanche.us17.list-manage.com/track/click?u=6653a830e4819c9e…; target="_blank">observation form</a>, email us (<a href="mailto:mtavalanche@gmail.com&quot; target="_blank">mtavalanche@gmail.com</a>), leave a VM at 406-587-6984, or Instagram (#gnfacobs).</p>

Backcountry Skiing and Stay-at-home Order

Park county is requesting anyone who is not a permanent resident or provider of essential service avoid all travel to Cooke City/Silvergate. This includes both single day and overnight visitors.

Please consider mellower terrain and lowering your risk to reduce potential for a needed rescue. Also consider that the distraction of current events may cloud our judgment which compromises our ability to safely attempt more challenging objectives. Take a step back. Ride Safe.

Observed this 8-12" slab on 3/30/20. Appears to have been triggered by cornice fall. Also observed several small wet loose slides from previous day and this morning. Photo: GNFAC

Bridger Range, 2020-03-31

Natural on Blackmore, North face.

Mt Blackmore
Northern Gallatin
Code
N-R3-D2.5
Latitude
45.44440
Longitude
-111.00400
Notes

I noticed a grey streak on Blackmore from my house on Baxter so I grabbed some weak binoculars (10x22) and could see a fairly large slide that originated somewhere in the shadows near the summit and stopped just above the trees in that bowl. Plenty big to take someone for a bad ride!

Number of slides
1
Number caught
0
Number buried
0
Trigger
Natural trigger
R size
3
D size
2.5
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Single Avalanche
Advisory Year