Bulletin d’avalanche

Summit Lake

Chugach National Forest Avalanche Center
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Danger d’avalanche

Tue
Alpin
4 · Fort
Limite forestière
4 · Fort
Sous la limite
3 · Marqué
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Points saillants

Dangerous avalanche conditions exist. A powerful storm is moving through the region today raising the avalanche danger to HIGH. Heavy rain, snow, and very strong winds will cause avalanches to release naturally in many areas and debris could run down avalanche paths into snow-free zones. Additionally, new snow avalanches could overload buried weak layers and create even larger avalanches. Travel in avalanche terrain is NOT recommended. 

Problèmes avalancheux

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Very Likely
    Taille
    2–3

    After a week of high pressure the first series of January storms is upon us. Unfortunately, these are again fairly warm storms with a rain line up to 2,000' or so. Ridgetop winds are increasing this morning from the east and should peak midday at 50-70 mph with gusts near 100 mph. Today is a day to let the storm do its thing without us being in the way.

    Storm totals from yesterday with expected snowfall today - all snowfall guesses are above 2000':

    • Girdwood: 1-1.5" water (~16" snow). Another 3-4" of water today (over 30" snow!)
    • Turnagain Pass: 0.7-1" water (10" snow). Another 2-3" of water today (over 20" snow)
    • Summit Lake: 0.3-0.5" water (3-5" snow). Another 1.5-2" of water today (over 15" snow)
    • Seward/Lost Lake: 1-1.5" water (10-15" snow). Another 2-3" water today (over 20" snow)

    Dry snow avalanches:  Above 2,000' there could be precipitation rates of 1-2" of snow per hour in Summit Lake. This is a textbook case for 'rapid loading', which results in natural storm snow avalanches. With 15+ inches of snow today, storm slabs could be 1-2' deep and quite large and dangerous. All this new snow is falling on weak faceted snow, which will only make it more likely for the new snow to avalanche. Many of the alpine slopes will see significant wind loading as well. New wind slabs could build up to 3' or deeper before they avalanche. Finally, cornices. These should be getting bigger with the wet sticky snow and when chunks of cornices fall off, they are likely to trigger slab avalanches below. 

    Wet snow avalanches:  We can safely assume that wet snow avalanches are occurring around 2,000' and below due to rain on snow. There is very little snow below 1,500' so these types of avalanches may be on the smaller side, but either way, avoiding any steep slope and staying out from under steep slopes above you are key for today. Some avalanches in the higher terrain could be large enough to run into snow-free zones.

     

    Predicted 24-hour snow accumulation by Tuesday morning. Precipitation is expected to pick up significantly today. Graphic courtesy of NWS Anchorage.

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    2–3

    In the higher elevations (above 2,500') there are several weak layers in the mid and base of the snowpack. These are mainly layers of buried surface hoar and facets. Storm snow avalanches today could 'step down' into these layers and a much larger avalanche may result. It will be interesting to see the extent of natural avalanche activity once skies clear. This is just another reason to avoid being in avalanche terrain. 

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