Lawinenlagebericht

Sawtooth & Western Smoky Mtns

Sawtooth Avalanche Center
Auf der Karte ansehen

Lawinengefahr

Mon
Hochgebirge
4 · Gross
Waldgrenze
3 · Erheblich
Unterhalb
3 · Erheblich
Open full map
Veraltet — dieser Lagebericht ist 3 years ago abgelaufen. Du siehst vergangene Verhältnisse, nicht den aktuellen Bericht.

Kernpunkte

Very dangerous avalanche conditions exist on upper elevation slopes. Large avalanches breaking underneath yesterday's snow will be easy to trigger and will continue to release naturally. Weak layers buried underneath thick, dense slabs can produce very large avalanches. While avalanches are most likely where the wind has been transporting snow, slides are also possible in sheltered terrain. Loose snow avalanches are likely on steep slopes and will occur naturally during periods of direct sun. 

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Very Likely
    Größe
    2–3.5

    When you head into the mountains today you will be dealing with a wintertime snowpack harboring the types of weak layers that we are used to dealing with in January and February (watch this video). We have two sets of weak layers that we are worried about, you can clearly see them both in the photo at right/above.

    1. March Weak Layers: Storms over the past 10 days built a 2-3+ foot thick slab on top of layers of weak snow formed earlier this month. Based on limited observations, these layers appear to be at their worst on slopes that face the sun, where crust+facet combinations exist. The slab over this weak snow is thick enough that avalanches failing on it are possible even in sheltered terrain. 
    2. February Weak Layers: A very dense, 3-6 foot thick slab of snow is uncomfortably resting on weak snow underneath. This combination was responsible for two historic natural avalanche cycles in mid-March. Very large natural avalanches failed on all aspects of the compass. The most recent triggered avalanche involving this snow occurred Friday in the Frenchman's drainage near Smiley Creek when riders remotely triggered a slide that broke 4-5 feet deep and 800+ feet wide (photo at right/above). The riders were at least 500 feet away on the ridgeline above when they triggered the slide. Blocks of snow the size of small cars remained intact as they traveled downslope, breaking green trees along the way. Triggering an avalanche involving this deeper weak layer is less likely than a slide higher in the snowpack, but the consequences would be devastating. 

    Yesterday's big storm and today's ongoing snowfall and wind loading are adding significant stress to these layers. Persistent slabs are challenging beasts to deal with. You can trigger them from long distances away from where the avalanche releases. Slides may break much wider and deeper than you expect, wrapping around large terrain features. Tracks on a slope are not an indicator of stability, these slides can fail after many skiers or riders have traversed a slope. Smaller avalanches can be effective triggers for these deeper weak layers as they travel downslope.

    (3/31/2023)

    Crown of a very large avalanche that was remotely triggered by riders from at least 500 feet away on the ridgeline above. It broke 4-5 feet deep and 800+feet wide. This slope faces W at 9,300' in the Frencman's drainage near Smiley Creek. You can clearly see the two sets of persistent weak layers in our snowpack in this photo. 

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Very Likely
    Größe
    1.5–2.5

    Remote weather stations are reporting 8-10" of new snow here, though observations on the ground indicate the actual totals are closer to 14-18". Snowfall was accompanied by moderate to strong winds blowing out of the W-SW during the day, switching to W-NW late in the day. Ongoing snowfall and wind today will continue to produce large, natural avalanches, particularly in upper elevation terrain. 

     You'll find large, reactive wind slabs on many slopes today, thanks to the amount of new snow and the strength of the wind. Look for signs that the wind has been at work such as ripples on the snow surface, dune-like drifts, and fresh cornices. If the snow you are moving through suddenly becomes deeper and denser you've likely found a fresh slab. Cracks shooting out from your skis or machine are a clear sign the slab is unstable. Look for slabs near ridgelines and adjacent to midslope terrain features like ribs and gullies. In the steep terrain of the Sawtooths, slabs also commonly form on the aprons below cliffs and couloirs as the snow cascades down from above.

    Avalanches failing within the new snow will be effective triggers for the deeper weak layers described above.

    ADDITIONAL DISCUSSION: Loose snow avalanches will be easy to trigger today, and will occur naturally during periods of direct sunshine. The steep, rocky terrain of the Sawtooths is great at producing large loose snow avalanches. If the sun pokes out for long be alert to the potential for these slides to be cascading downward. 

    Read the Forecast Discussion below for more information about the range of problems you may encounter today. 

Avalanche Discussion

When you head into the backcountry today you'll be met with a number of avalanche problems and a snowpack that looks like it is February, not April. The persistent slab problems described above will be the primary driver of your terrain selection. These weak layers can produce avalanches that break hundreds to thousands of feet wide, wiping out entire alpine cirques and bowls. No thanks.

Next on the list are the large wind slabs that formed yesterday and overnight. The wind is still blowing and it hasn't run out of ammunition yet. These slabs will continue to grow today, and some additional light snowfall will be more fodder for the wind to build slabs out of. The wind slabs you encounter today will easily be large enough to bury you. 

In addition to these problems, here are a few things to keep in mind:

  • There is a lot of loose snow sitting around in the mountains right now. Today's sunshine will quickly warm up the new snow, causing a round of solar-initiated loose snow avalanches. In areas where the sun is staying out for longer these slides will develop a wet character. Natural slides are most likely on slopes that face the sun, but you'll be able to trigger these slides on many slopes. These slides can pick up speed quickly and entrain a lot of debris.
  • Low elevation terrain got a good freeze last night, but it won't take the sun long to heat things back up. A little bit of fresh snow on top will help accelerate this process. If the snowpack is becoming wet and mushy be alert to the possibility of wet loose snow avalanches that gouge deeply into the snowpack. 
  • Cornices have grown to massive sizes this year. Yesterday's storm and today's wind is helping them grow as you read this. Cornices that fail can be very effective triggers for deeper weak layers. Be cautious in your travels around these beasts—they behave in unpredictable ways and can catch even very experienced travelers off guard.
  • Slick, icy crusts exist underneath the new snow on slopes that face the sun. Loose snow and slab avalanches that fail above these crusts can run fast on far.

The powder skiing and riding are excellent right now, and the snow coverage is amazing. If you head out today you may find yourself enjoying one of your best days of the season.  Don't let this distract you from the hazards in the mountains. There is a surefire way to ruin your day—by triggering and being caught in an avalanche. Make a conservative plan for today, one that takes into account the wide range of hazards out there. 

Abgedeckte Regionen