GNFAC Avalanche Forecast for Tue Mar 24, 2020
<p>One to three inches of new snow fell across our advisory area with moderate winds predominantly from the southwest. This weekend skiers near Big Sky triggered small avalanches where the wind had drifted snow (<a href="https://www.mtavalanche.com/node/22498"><strong>photo and details</strong></a>, <strong><a href="https://www.mtavalanche.com/images/20/small-soft-slab-debris-near-beehi…;)</strong>. In steep terrain avalanches like this could easily push you into or off obstacles such as trees, gullies and cliffs. Look for cracks extending from your skis or sled to indicate this instability. If you find it, move to another area. While not ubiquitous, several groups have found surface hoar, a new weak layer, buried under the new snow (<a href="https://www.mtavalanche.com/images/20/surface-hoar-near-buck-ridge"><st…;). Skiers near Big Sky and Cooke City have identified this layer on some slopes but not others. Dig down a couple of feet and look for a stripe in your snowpit wall and propagation in your stability tests. The wind will also continue to build cornices and are ripe for collapse (<strong><a href="https://www.mtavalanche.com/images/20/large-cornices-lionhead-ridge">ph…;). The cornice collapse alone is dangerous, but it could also be the trigger that initiates a deeper avalanche such as one outside our advisory area in the Absaroka Mountains on Friday (<strong><a href="https://www.mtavalanche.com/node/22491">photos and details</a></strong>).</p>
<p>Dry snow avalanches breaking near the surface will be our primary concern today. However, wet snow avalanches and deep slab avalanches should be on your radar. Cooler temperatures and snow will minimize wet snow avalanches at high elevations, but if snow turns to rain at lower elevations the snowpack will quickly become unstable and it is time to move on. After several weeks of relative quiet, on Friday two separate groups of skiers south of Livingston (outside our advisory area) unintentionally triggered avalanches failing on deeply buried weak layers. The same day, unstable test results on sugary depth hoar drove our decision to turn around before arriving at our objective in the Taylor Fork (<a href="https://www.youtube.com/watch?v=PLgEkwzjb88&list=PLXu5151nmAvSbcbVf…;). An avalanche on this layer is unlikely but dangerous. The most likely ways to trigger this unlikely event are to find an area where the snowpack is thin or to be in the area when a cornice falls.</p>
<p>The avalanche danger is MODERATE on wind-loaded slopes and LOW on non-wind-loaded slopes. Assess the stability of the new snow, limit your time underneath cornices and take a couple of steps back in order to minimize stress on an already taxed medical system.</p>
<p>We will end daily avalanche forecasts on April 5th and continue with general bulletins every Monday and Friday through April. Over the next couple of weeks, we will take down weather stations and will no longer receive observations from guides and ski patrols. 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" target="_blank">mtavalanche@gmail.com</a>), leave a VM at 406-587-6984, or Instagram (#gnfacobs).</p>
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Small soft slabs northern Madison range
From obs: "Was out today and found buried surface hoar 10-15 cms down. Some previous natural activity on this layer on steeper north aspects with very shallow soft slabs, but mostly dry loose at this point. Not much slab formation since the last ppt event. This could be a problem when more snow and wind in the next few days."
"Was out today and found buried surface hoar 10-15 cms down. Some previous natural activity on this layer on steeper north aspects with very shallow soft slabs, but mostly dry loose at this point. Not much slab formation since the last ppt event. This could be a problem when more snow and wind in the next few days." Photo: T. Woodward
Forecast link: GNFAC Avalanche Forecast for Tue Mar 24, 2020GNFAC Avalanche Forecast for Wed Mar 25, 2020
Obs: "School bus size cornices over Easterly portions of Lionhead Ridge. It is hard to tell from the photo, but the largest cornices were about 20-25' tall. We dug a few pits on East Facing slopes between 9,000-9,500 ft with the worst result being an ECTN-21 however these Cornices are primed and ready to fall with the abundant sunshine and warming weather." Photo: JR
Forecast link: GNFAC Avalanche Forecast for Tue Mar 24, 2020
Wet loose slides near Big Sky
From e-mail: "Natural wet slides [on 3/21]... caused us to back off our plan of heading that way and ski a north, shady a aspect instead. On a southern as aspect t 9000ft at 1:30pm we dug a hasty pit and observed a wea weak layer out 1m down. The facets were beginning to round." Photo: K. Master
From e-mail: "Natural wet slides... caused us to back off our plan of heading that way and ski a north, shady aspect instead. On a southern aspect. 9000ft. 1:30pm. We dug a hasty pit and observed a weak layer about 1m down. The facets were beginning to round." Photo: K. Master
Forecast link: GNFAC Avalanche Forecast for Tue Mar 24, 2020
GNFAC Avalanche Forecast for Mon Mar 23, 2020
<p>Today the snowpack is generally stable, but travel in avalanche terrain always comes with risk. Although unlikely, there are three avalanche problems to keep in mind. Wet loose avalanches, isolated wind slabs, and weak sugary snow at the base of the snowpack.</p>
<p>Wet loose slides and wind slabs may be small, but have large consequences if they push you into terrain traps like trees or over cliffs. Avoid sunny slopes if the snow surface becomes wet, if you sink past your ankle in wet snow or see wet roller-balls on the surface. Where the snow surface is dry, carefully assess terrain for wind loading and consequences of even a small slide. A recent skier triggered wind slab near Big Sky shows the potential type of hazard today (<a href="https://www.mtavalanche.com/node/22498"><strong>photo and details</strong></a>).</p>
<p>Avalanches on weak layers near the ground are unlikely, but have big consequences. On Friday two separate groups had close calls in the Absarokas (outside the advisory area) with large avalanches that broke deep in the snowpack. One was triggered by a cornice fall (<a href="https://www.mtavalanche.com/node/22491"><strong>photos and details</strong></a>), and the other on a slope with over a dozen previous tracks (<a href="https://www.mtavalanche.com/node/22486"><strong>photos and details</strong></a>). Dave skied in Taylor Fork and backed off a plan to ski steep terrain after he dug and found a poor snowpack structure (<a href="https://www.youtube.com/watch?v=PLgEkwzjb88&list=PLXu5151nmAvSbcbVf…;). Probe and dig to look for weak sugary snow at the base of the snowpack before riding steep slopes, and keep an eye out for surface hoar buried about 8” deep (<a href="https://www.mtavalanche.com/images/20/surface-hoar-near-buck-ridge"><st…;). Stay far back from the edge along ridgelines and minimize time on slopes with large cornices above.</p>
<p>Today the avalanche danger is rated LOW, but avalanches are not impossible. Continue to practice safe backcountry travel protocols and be diligent with snowpack and terrain assessment.</p>
<p>We will end daily avalanche forecasts on April 5th and continue with general bulletins every Monday and Friday through April. Over the next couple weeks we will take down weather stations and get little to no observations from guides and ski patrol. With more people in the backcountry and ski areas closed, 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" target="_blank">mtavalanche@gmail.com</a>), leave a VM at 406-587-6984, or Instagram (#gnfacobs).</p>