19-20

Snowmobile triggered slab Portal Creek

Portal Creek
Northern Gallatin
Code
SS-AMu-R2-D2-O
Latitude
45.28900
Longitude
-111.14100
Notes

From obs. 4/4/20: "Avalanche today up portal creek. 2 1/2 ft crown and 4 - 5 ft runout. Triggered by snowmobile. Everyone was safe!"

Number of slides
1
Number caught
0
Number buried
0
Avalanche Type
Soft slab avalanche
Trigger
Snowmobile
Trigger Modifier
u-An unintentional release
R size
2
D size
2
Bed Surface
O - Old snow
Problem Type
Persistent Weak Layer
Slab Thickness
30.0 inches
Slab Thickness units
inches
Single / Multiple / Red Flag
Single Avalanche
Advisory Year

GNFAC Avalanche Forecast for Sat Apr 4, 2020

Snowpack and Avalanche Discussion

<p>Winds picked up yesterday, building fresh drifts that can be triggered by a skier or rider today. Skiers in the Bridger Range yesterday saw rapid wind loading near the ridge. Be skeptical of any recently wind-loaded slope and steer clear of fresh drifts. If you feel the snow surface stiffen and see cracks shoot out in front of you, you’ve found one of these drifts and should carefully retreat out of steep terrain.</p>

<p>Avalanches can also break on weak layers buried 2-3 feet deep. It’s worth digging down to look for these weak layers, as not every slope has them. Yesterday, Doug found good stability on a west facing slope in Beehive Basin with a number of ice crusts in the upper snowpack that were well bonded (<strong><a href="https://www.youtube.com/watch?v=1j2Y8NWOuHs&amp;list=PLXu5151nmAvSbcbVf…;), but noted that other slopes have surface hoar or near surface facets instead. Skiers near Ross Pass yesterday got a big collapse on facets near an ice crust as they stepped out of their skis to dig a snowpit (<strong><a href="https://www.mtavalanche.com/node/22653">details</a></strong&gt;). They took that clear sign of instability as a clue to avoid steep terrain and chose an alternative, mellower, route back to the trailhead. Just to the south, a different group found buried surface hoar and got unstable test results. A collapse and unstable test results are evidence that the potential still exists to trigger avalanches on these layers. Careful analysis of these layers is needed before committing to steep terrain.</p>

<p>Temperatures are going to rise another 5 degrees warmer than yesterday. With sunny skies this afternoon, the snow surface will become wet, lose cohesion and become unstable. Watch for roller balls and pinwheels as clues that this process is starting. Plan to be off steep, sun exposed slopes by early afternoon to avoid triggering a wet snow avalanche.</p>

<p>&nbsp;</p>

<p>The avalanche danger is rated MODERATE across our advisory area.</p>

<p>We are ending daily avalanche forecasts <strong>tomorrow</strong> Sunday, April 5<sup>th</sup> and will post general weather and avalanche bulletins every Monday and Friday through April. Continue to send us your observations. You can fill out an observation form, email us (mtavalanche@gmail.com), leave a VM at 406-587-6984, or Instagram (#gnfacobs).</p>

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Closures 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)”.

Large collapse near Ross Peak

Ross Peak
Bridger Range
Code
Latitude
45.85860
Longitude
-110.95600
Notes

From obs: "Approached a lower angle east facing test slope around 8000 with similar aspect to ski objective. As I stepped out of my skis to dig a pit, we heard a large collapse. Slope we were on was not steep enough to slide but we had our answer. Moved off that slope, dug a quick hasty pit CT12, 1.5 ft down on facets below ice crust, clean shear. Skied down an alternate conservative way."

Number of slides
0
Number caught
0
Number buried
0
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Red Flag
Advisory Year

GNFAC Avalanche Forecast for Fri Apr 3, 2020

Snowpack and Avalanche Discussion

<p></p>

<p>With warmer temperatures, sunny skies, more than a foot of new snow this week and buried weak layers, we have a number of different avalanche concerns today (<a href="https://youtu.be/s5ED_1T3leE"><strong>video</strong></a&gt;).</p>

<p>All our concerns today are within the upper snowpack. Three different groups of skiers triggered avalanches yesterday within the new snow in the Bridger Range (<strong><a href="https://www.mtavalanche.com/node/22644">details</a></strong&gt;) and a small natural was seen near Cooke City (<strong><a href="https://www.mtavalanche.com/images/20/natural-new-snow-cooke">photo</a>…;). Even more slides were reported the day before (see full list <a href="https://www.mtavalanche.com/avalanche-activity"><strong>here</strong></…;). While instabilities within the new snow will be healing, you could still trigger a similar slide today, particularly on wind-loaded slopes. Be wary of wind-loaded pockets and watch for cracks shooting out from your skis as a sign the new snow remains unstable.</p>

<p>You could also trigger a slide on weak layers buried 2-3 feet deep. Depending on the slope you’ll find surface hoar, near surface facets, or an ice crust with poor bonding. It doesn’t really matter what the weak layer consists of, it won’t stabilize as quickly as the new snow. With a patchy distribution, your best mitigation strategy is to dig down to look for and test these layers before getting into avalanche terrain.</p>

<p>With sunshine and warmer temperatures, wet avalanches are also a concern today, especially as the day heats up on sunny slopes. As the snow surface becomes wet and sticky, it’s time to move out of steep terrain. Roller balls and pinwheels are telltale signs that the snow is on its way to becoming wet and unstable.</p>

<p>With both wet and dry avalanches possible, the avalanche danger is rated MODERATE.</p>

<p>We are ending daily avalanche forecasts this Sunday, April 5<sup>th</sup> and will post general weather and avalanche bulletins every Monday and Friday through April. Continue to send us your observations. You can fill out an observation form, email us (mtavalanche@gmail.com), leave a VM at 406-587-6984, or Instagram (#gnfacobs).</p>

Closures 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)”.