Snowpack and Avalanche Discussion
<p>The weather and spring storms are the primary drivers of this week’s avalanche danger. To start off the week, there are significant differences in the weather throughout the forecast area, with significant snowfall in some areas (Bridger Range), moderate accumulation in others, (south of Bozeman, Big Sky, and Cooke City) and a few ranges receiving more rain than snow (Lionhead and Centennial Ranges).</p>
<p><strong>Here’s what we know:</strong></p>
<ul>
<li>The snowpack was mostly stable before Sunday/ Monday’s storm.</li>
<li>The more <em>new </em>snow there is, the more likely you are to encounter avalanches and the larger their potential size. Slides will fail within the new and wind-drifted snow as <strong>storm slab </strong>and<strong> wind slab avalanches. </strong>Deeper depths of new snow generally equate to more significant avalanche danger.</li>
<li>Rain on snow has a destabilizing effect as the bonds that hold the snowpack together break apart.</li>
<li>Expect <strong>wet loose avalanches</strong> as the new snow warms. These may run long distances on underlying crusts.</li>
</ul>
<p><strong>What to do:</strong></p>
<ul>
<li>Evaluate new snow depths and expect these to change with elevation.</li>
<li>If your travel plans take you to slopes steeper than 30 degrees, assess how the new and wind-drifted snow is bonding to the old snow surface by watching for clear signs of instability, such as avalanches and shooting cracks. A quick, extended column test 1-2 feet deep can provide additional information.</li>
<li>If rain fell on the snowpack and as temperatures warm, breaking through an unsupportable and slushy snowpack, seeing pinwheels of wet snow and small wet slides are indicators of wet snow instability.</li>
</ul>
<p><strong>Moving forward through the week, </strong>Tuesday's temperatures will climb well above freezing. <strong>Wet loose avalanches </strong>will run long distances on firm crusts underlying the new snow. These slides will be most concerning in areas where the most snow fell. A shift to cooler, north-facing aspects may be enough to ward off the wet snow danger.</p>
<p>Depending on midweek snowfall amounts, the avalanche danger may increase again Tuesday night into Wednesday before settling into the spring rhythm of stable conditions in the morning while snow surfaces are cold and frozen, and less stable by late morning as temperatures climb into the 50 and 60 degree F range under sunny skies toward the end of the week.</p>
<p>We have had a long and wonderful season. <em>So far</em>, there have been no avalanche fatalities within our forecasting area. Keep up the good work, and don’t let your guard down. We want to keep it that way. Assess how the new snow is bonding, avoid slopes with active wind-loading, and evaluate the snowpack for changing conditions as temperatures warm and cool again.</p>
<p><span>See our website for more general spring snowpack and travel advice. </span></p>
