17-18

<p>Wind slabs are the primary concern across the advisory area. On Monday, wind loaded slopes failed naturally and with human triggers (<a href="https://youtu.be/l7Msb_dLZ70"><strong>video</strong></a&gt;, <strong><a href="https://www.mtavalanche.com/images/18/natural-wind-slab-n-bridgers">pho…;). Yesterday, calmer and drier conditions&nbsp;gave wind loaded slopes a chance to gain strength. On our tour in Beehive Basin yesterday, we found wind loaded slopes to be less reactive (<strong><a href="https://www.youtube.com/watch?v=I4bf_gEizsI">video</a></strong&gt;), which is consistent with observations from both Big Sky and Bridger Bowl Ski Patrols.</p>

<p>However, a separate observation form the northern Madison Range reported a wind loaded slope being remotely triggered by a skier’s dog (<strong><a href="https://www.mtavalanche.com/images/18/remotely-triggered-wind-slab-nort…;). This slope was heavily loaded by west-southwest winds. This is bull’s eye information that wind loaded slopes should be evaluated carefully and deserve respect.</p>

<p>Watch for areas of wind drifted snow near upper elevation ridgelines and cross loaded terrain features. Cornices are visual clues that underlying slopes could be heavily wind loaded. Use quick hasty pits or small test slopes to evaluate stability before committing to consequential terrain.</p>

<p>Outside of wind loaded slopes the snowpack is generally stable.</p>

<p>Today, human triggered avalanches are possible on wind loaded slopes which have a <strong>MODERATE</strong> avalanche danger. Non-wind loaded slopes have a <strong>LOW</strong> avalanche danger.</p>

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

<p>The storm has ended and snowfall totals are 12” around Bozeman and 16” around Big Sky and Cooke City. The snow density was near 10% with a measured <a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/or/snow/?cid=nrcs142p2… water equivalent</a> of 1.2” to 1.6”. This new snow avalanched easily yesterday, on both wind-loaded and non-wind-loaded slopes as this short <strong><a href="https://youtu.be/l7Msb_dLZ70">video</a></strong&gt; shows. Wind yesterday and last night drifted snow into slabs at least 2’ thick that will be easy to trigger. Although the snowfall has stopped, slopes are still unstable. Fortunately, the older snow is strong and avalanches breaking deep are not expected. Alex was in Cooke City on Friday and Saturday and was able to trigger wind-slabs (<strong><a href="https://youtu.be/epeP85qLoHg">video</a></strong&gt;). This new wind-blown snow will react similarly around Bozeman, Big Sky and Cooke City today.</p>

<p>Yesterday, new snow and wind created widespread avalanches. Today requires careful snowpack evaluation since signs of instability are decreasing, such as cracking, collapsing, and natural avalanches. For today, the avalanche danger is rated <strong>CONSIDERABLE</strong> on all wind-loaded slopes since triggering slides is likely. On slopes without a wind-load, triggering slides is still possible and the danger is rated <strong>MODERATE</strong>.</p>

<p>The southern Madison and southern Gallatin Ranges recorded a storm total of 9” of snow (.8” <a href="http://www.or.nrcs.usda.gov/snow/about/swe.html">SWE</a&gt;) with Lionhead getting 4”. Today’s avalanche concern is with this new snow, especially if it has been blown into wind slabs. Additionally, winds made cornices bigger and easier to trigger (<a href="https://www.mtavalanche.com/images/18/cornice-triggered-avalanche-near-…;). Be extra careful on wind-loaded slopes and be suspect of cornices breaking far back from their edge. In general, older snow is strong, and deeper avalanches are unlikely. For today, the avalanche danger is rated <strong>MODERATE</strong> on all slopes.</p>

<h3>Wet Snow Avalanches</h3>

<p>April sunshine, no matter how brief, will begin to melt the snow surface and create wet avalanches. I do not expect this to be widespread, but if you witness pinwheels rolling downhill I would anticipate wet loose avalanches will follow.</p>

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

<p>Heavy snowfall will continue today and create an unstable snowpack and dangerous avalanche conditions, and stability will decrease through the day. New snow instabilities will be widespread. Below today’s new snow, the snowpack is 8-12 feet deep and generally stable.</p>

<p>The mountains near Bozeman, Big Sky and Cooke City have 6-10” of new snow equal to 0.6-1” of snow water equivalent (SWE), and could have a total of 12-18” of new snow by the end of today. Strong wind this afternoon will drift this snow into slabs 2-4’ thick that are easy to trigger and could break naturally. The heavy new snow fell on a variety of old snow surfaces, from crusts on southerly aspects to dry new snow on higher, shadier aspects. Avalanches may break within or below the new snow, and will bond variably across aspects and elevations.</p>

<p>Danger will increase through the day and stability assessment will be tricky. Conservative terrain selection is the key to avoid dangerous avalanches today. Avoid travel on and below steep wind loaded slopes, and avoid slopes steeper than 35 degrees. Avalanche danger is <strong>CONSIDERABLE</strong> on all slopes this morning and will rise to <strong>HIGH</strong> on wind loaded slopes this afternoon.</p>

<p>The mountains near West Yellowstone and the southern Madison and Gallatin ranges received just 1” of snow overnight and are expected to get 3-5” today. Avalanche concerns will be fresh wind slabs from new snow and moderate west-northwest wind today, and large cornices (<strong><a href="https://www.mtavalanche.com/images/18/cornice-triggered-avalanche-near-…;). Avoid wind loaded slopes if you see blowing snow and/or cracking of fresh drifts and be extra cautious of steep slopes if snowfall is heavier than expected today. Keep a far distance back from the edge of cornices and avoid slopes directly below them. The snowpack below today’s snow is generally stable and deeper avalanches are not likely. New snow and wind today will make avalanches possible and avalanche danger is <strong>MODERATE</strong> on wind loaded slopes and <strong>LOW</strong> on non-wind loaded slopes.</p>

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