18-19

GNFAC Avalanche Forecast for Mon Mar 25, 2019

Snowpack and Avalanche Discussion

<p>Near Cooke City received 6” of snow equal to 0.4” <a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/or/snow/?cid=nrcs142p2… water equivalent</a> (SWE), and near Big Sky and Hyalite got 2-3” equal to 0.2” SWE. This new snow makes loose snow avalanches possible. These avalanches can slide long distances on firm, refrozen surfaces below the new snow, and they will become more likely with the first rays of sunshine and above freezing temperatures. This afternoon increasing wind will form small fresh drifts that can be triggered by a person. Be cautious of steep, wind loaded slopes if you see blowing and drifting snow or cracking of fresh drifts.</p>

<p>The snowpack is generally stable below the new snow, and avalanches today will mostly be small. Even small slides are hazardous or deadly if they carry you over cliffs, rocks or through trees. Before riding steep terrain carefully assess the stability of the new snow and consequences of being caught in a slide. Today, new snow makes avalanches possible and avalanche danger is <strong>MODERATE</strong>.</p>

<p>The Bridger Range, southern Madison and Gallatin ranges and mountains near West Yellowstone received&nbsp;less than an inch of snow, and this morning the snowpack is generally stable. On mid-low elevation slopes and slopes that receive direct sun there is a stable, supportable frozen crust on the surface of a wet snowpack. On high elevation shady slopes the snowpack is dry and generally stable (<u><strong><a href="https://www.youtube.com/watch?v=YvYdU9j52zM&amp;index=2&amp;t=0s&amp;li…;

<p>This afternoon above freezing temperatures and sunshine will increase the possibility of wet snow avalanches. Yesterday Ian toured north of Bridger Bowl and Eric toured in Beehive Basin. They both found the crust on the snow surface was supportable and stable for most of the day. This morning cloudy skies will create similar conditions. Avoid steep slopes if the snow surface becomes wet and unsupportable, or if you sink above your boots in wet snow (<u><strong><a href="https://www.youtube.com/watch?v=YvYdU9j52zM&amp;index=2&amp;t=0s&amp;li…;

<p>Over the past week there were natural and human triggered wet slab avalanches during warm, sunny days (<u><strong><a href="https://www.mtavalanche.com/photos">photos page</a></strong></u>), including one that partially buried a rider (<u><strong><a href="https://www.mtavalanche.com/node/20467">details</a></strong></u&gt;) and one that surprised a couple skiers (<u><strong><a href="https://www.mtavalanche.com/node/20485">details</a></strong></u&gt;). Today similar avalanches are possible if above freezing temperatures and sunshine create a wet snowpack. Avalanche danger is <strong>LOW</strong> this morning and will rise to <strong>MODERATE</strong> this afternoon.</p>

<p>If you get out and have any avalanche or snowpack observations to share, contact us via our <u><a href="https://www.mtavalanche.com/node/add/snow_observation">website</a></u&gt;, email (<u><a href="mailto:mtavalanche@gmail.com">mtavalanche@gmail.com</a></u&gt;), phone (406-587-6984), or Instagram (#gnfacobs).</p>

Upcoming Avalanche Education and Events

Events and Education Calendar.

GNFAC Avalanche Forecast for Sun Mar 24, 2019

Snowpack and Avalanche Discussion

<p>The past week of daily above freezing temperatures and sun created a wet snowpack on mid-low elevation slopes and slopes that receive direct sunshine. Overnight, below freezing temperatures formed a frozen crust on the snow surface which makes the snowpack generally stable this morning. Today, above freezing temperatures and some sunshine will melt this crust and make wet snow avalanches possible. Cloud cover and snowfall this afternoon will reduce wet snow avalanche activity, but any rain will weaken the snowpack and increase the chances of natural and human triggered avalanches. If the snow surface is wet and unsupportive move to lower angle or cooler, shady slopes.</p>

<p>Yesterday afternoon skiers in the northern Bridger Range triggered a small, powerful wet slab (<strong><a href="https://www.mtavalanche.com/node/20485">details</a></strong&gt;). This is a reminder that wet slab season is here,&nbsp;and is similar to a timber sled triggered avalanche that buried a rider up to his waist on Thursday (<strong><a href="https://www.mtavalanche.com/node/20467">details</a></strong&gt;). Yesterday we went to Saddle Peak and found a wet, unstable snowpack on sunny slopes and the surface crust melted by late morning. We found a dry, generally stable snowpack on high elevation shady slopes (<strong><a href="https://www.youtube.com/watch?v=YvYdU9j52zM&amp;index=2&amp;t=0s&amp;li…;

<p>See our <strong><a href="https://www.mtavalanche.com/photos">photos page</a></strong> for a look at recent natural and human triggered wet slab avalanches. Today these types of slides are possible on slopes where the snow surface is wet and unsupportive. Even small wet slabs can be powerful and the debris sets up like concrete. Be cautious of steep terrain above you where natural wet slides could start, similar to a slide on the Sourdough Canyon trail last Thursday (<strong><a href="https://www.mtavalanche.com/node/20471">details</a></strong&gt;). Anticipate decreasing stability as temperatures warm through the day, especially on low elevation slopes and slopes that receive direct sun. The avalanche danger is <strong>LOW</strong> this morning and will rise to <strong>MODERATE</strong> this afternoon.</p>

<p>If you get out and have any avalanche or snowpack observations to share, contact us via our <u><a href="https://www.mtavalanche.com/node/add/snow_observation">website</a></u&gt;, email (<u><a href="mailto:mtavalanche@gmail.com">mtavalanche@gmail.com</a></u&gt;), phone (406-587-6984), or Instagram (#gnfacobs).</p>

Upcoming Avalanche Education and Events

Events and Education Calendar.

Natural wet slab Blackmore

Mt Blackmore
Northern Gallatin
Code
WS-N-R1-D1.5-G
Elevation
7400
Aspect
W
Latitude
45.46630
Longitude
-110.98400
Notes

Skiers in Hyalite saw a natural wet slab near Blackmore Lake. From the email: "The slide was located around 300 yards South of Blackmore Lake on a West facing slope at an elevation just above 7400 feet.  It broke below a cliff band about 3' deep (to the ground) and ran a few hundred feet (almost to the skin track)." Photo: JR Mooney

Number of slides
1
Number caught
0
Number buried
0
Number killed
0
Avalanche Type
Wet slab avalanche
Trigger
Natural trigger
R size
1
D size
1.5
Bed Surface
G - Ground
Problem Type
Wet Snow
Slab Thickness
36.0 inches
Vertical Fall
100ft
Slab Width
30.00ft
Slab Thickness units
inches
Single / Multiple / Red Flag
Single Avalanche
Advisory Year

Skiers in Hyalite saw a natural wet slab near Blackmore Lake. From the email: "The slide was located around 300 yards South of Blackmore Lake on a West facing slope at an elevation just above 7400 feet.  It broke below a cliff band about 3' deep (to the ground) and ran a few hundred feet (almost to the skin track)." Photo: JR Mooney

Avalanche Details: Natural wet slab Blackmore
Northern Gallatin, 2019-03-23

Skier triggered wet slab N. Bridgers

Northern Bridgers
Bridger Range
Code
WS-ASu-R2-D1.5-O
Elevation
7500
Aspect
SE
Notes

From e-mail: "while skiing a short, SE-facing slope, we triggered a wet slab avalanche. We both skied to the side, but it was a real wakeup call to the current snowpack. Going from below freezing all winter to sudden warming has left a lot of layers. We didn't measure the slope angle, but it couldn't have been more than 32 degrees in the starting zone. The slide was slightly to skier's right of the slope, and the middle of the slope was only 6" deep, but much deeper where the slide occurred. Maybe 30-40' wide at the crown, ran 80'.

Number of slides
1
Number caught
0
Number buried
0
Avalanche Type
Wet slab avalanche
Trigger
Skier
Trigger Modifier
u-An unintentional release
R size
2
D size
1.5
Bed Surface
O - Old snow
Problem Type
Wet Snow
Slab Thickness
16.0 inches
Vertical Fall
80ft
Slab Width
35.00ft
Slab Thickness units
inches
Single / Multiple / Red Flag
Single Avalanche
Advisory Year