21-22

<p>The snowfall from Monday night and Tuesday dropped 10-16” in the mountains around Cooke City, Hyalite and Big Sky. Wind during the storm loaded slopes even more. Because of the warm weather today, wet avalanches will make a comeback which means both wet and dry avalanches have to be considered. Avoiding dry avalanches requires digging and testing.&nbsp; Triggering avalanches at the interface between the old and new snow or on layers of weak snow 2-3 feet deep remains possible.&nbsp;</p>

<p>The wet snow avalanche danger will rise along with the sun. Slopes getting direct sunshine will soften, melt and trigger numerous point release, loose-snow avalanches by this afternoon, just as Ian warned in his latest <a href="https://youtu.be/BUewVJ3jjhc"><strong><u>video</u></strong></a&gt;. Although wet avalanches are very different from dry slides, one can trigger another: a wet slide can trigger deeper, dry layers and avalanches that are dry in the starting zone can be wet further down the path. It is not uncommon to be unpleasantly surprised with unusual avalanches when temperatures rise above freezing for the first time in dry snow. Travel conservatively and avoid slopes that are getting wet. For today, the danger is rated MODERATE on all slopes, for both wet and dry avalanches.</p>

<p>The Bridger Range and mountains south of Big Sky to West Yellowstone received 4-6” of snow earlier in the week. Dry snow avalanches are unlikely today, but wet, loose snow avalanches will happen quickly in the thin, new snow. Intense sunshine will wet the new snow and the underlying ice crust will be a sliding surface once water starts to flow on it. Pinwheels and roller balls are signs the snow is getting wet enough to avalanche.&nbsp;</p>

<p>If you get out early and stick to dry powder the avalanche concern are wind drifts that formed Tuesday. Dave was in the Bridger Range that day and had some crack and break (<a href="https://youtu.be/8UnSYrlAAl4"><strong><u>video</u></strong></a&gt;). Although the likelihood of triggering these drifts has decreased, it’s not impossible, so dig and test before committing to serious avalanche terrain. In general, the dry snow avalanche is rated LOW. The wet snow avalanche danger will increase through the morning and sunny slopes with moist snow will have a MODERATE danger.</p>

<p>Our last daily forecast will be issued on Sunday. During the rest of April we will issue weather and avalanche updates Monday and Friday. Please continue sending us your observations. You can submit them via our website, email (mtavalanche@gmail.com), phone (406-587-6984), or Instagram (#gnfacobs).</p>

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<p>The mountains around Cooke City received 16” of snow equal to 1.6” of <a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/null/?cid=nrcseprd1314… water equivalent</a> (SWE) in the last two days, creating dangerous avalanche conditions. Strong winds built slabs of drifted snow that are likely to avalanche. Avoid steep, wind-loaded slopes where large avalanches are the most likely. Watch for the stiffening of the snow surface and increasing depth in unusual locations because strong winds spared few areas. A small drift could be dangerous when combined with terrain features such as cliffs or trees (<a href="https://www.mtavalanche.com/images/22/wind-drift-bridger-range"><strong…;).</p>

<p>On slopes unaffected by the wind, evaluate the stability carefully by assessing how the new snow bonded to the old snow surface and checking for weak layers buried 2-3’ deep. While slides breaking within the old snow are less likely after last week’s warm-up, the resulting avalanche would be large and destructive.</p>

<p>Today, human-triggered avalanches are likely, and the danger is CONSIDERABLE.&nbsp;</p>

<p>Heightened avalanche danger exists in the Northern Gallatin and Northern Madison Ranges where 9-11” of snow (0.9-1.1” of SWE) fell in the last two days. Strong winds stripped snow from some slopes and loaded it onto others. During avalanche mitigation work, the Big Sky Ski Patrol triggered slides up to 2’ deep in wind-loaded terrain. A much smaller avalanche was responsible for injuries to a skier near Wilson Peak a day prior to the storm (<a href="https://www.mtavalanche.com/accident/22/04/04"><strong>details and photos</strong></a>). Ian and his partner listed wind-drifted snow as their primary avalanche concern with an additional warning that the wet snow avalanche danger will rise as the new snow warms (<a href="https://youtu.be/BUewVJ3jjhc"><strong>video</strong></a&gt;).</p>

<p>On isolated slopes, a layer of sugary facets makes deeper avalanches possible (<a href="https://www.youtube.com/watch?v=0w18Fxp-dmI"><strong>Flanders video</strong></a>).</p>

<p>Today, select low-angle terrain if you observe signs of wind-loading (<a href="https://www.mtavalanche.com/images/22/wind-drift-bridger-range"><strong…;) or instability such as recent avalanches, shooting cracks or collapsing. Human-triggered avalanches are possible and the danger is MODERATE.</p>

<p>In the Bridger, Southern Madison and Southern Gallatin Ranges and the Lionhead area, 4-6” of new snow fell in the last two days accompanied by strong winds. Yesterday, north of Bridger Bowl, I found that strong winds created drifts on many slopes and planned to avoid them on larger alpine faces and in technical terrain (<a href="https://www.youtube.com/watch?v=8UnSYrlAAl4"><strong>video</strong></a>…;

<p>Wet snow avalanches will become a concern later this afternoon or tomorrow. If you see wet rollerballs or pinwheels of snow coming down the slope, the danger is increasing, move to shadier aspects.</p>

<p>Today, human-triggered avalanches are possible on wind-loaded slopes where the danger is MODERATE. The danger is LOW on all other slopes. Avalanches breaking deeper in the snowpack are unlikely but not impossible.</p>

<p>If you get out, please send us your observations no matter how brief. You can submit them via our website, email (mtavalanche@gmail.com), phone (406-587-6984), or Instagram (#gnfacobs).</p>