Bollettino valanghe

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Valdez Avalanche Center
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In sintesi

Avalanche danger will transition from Moderate to Considerable throughout the day today. New snow accumulation will create storm slabs up to a foot deep that are likely to be sensitive to human triggers by the end of the day. Deeper slabs will be expected in alpine terrain where wind has redistributed the snow. 

Problemi valanghivi

  • Storm Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–2

    With significant snowfall expected over the next 48 hours, we will see the formation of storm slabs in all zones. At the moment there has been little new snow accumulation but we can expect widespread storm slabs 6-10 inches deep by the end of the day at higher elevations. Gusty ridgetop winds will redistribute this snow into deeper pockets on leeward slopes. 

    Cold faceting surface snow has been observed in areas to the North of Thompson Pass creating a potential weak layer under the new storm slab. Additionally, persistent slabs that have been observed over the last week may become stressed with the new snow load. 

     

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    Persistent windslab 6 inches to a foot thick that formed last week are beginning to become stubborn to triggers but may still pose a threat in isolated areas. In mid to high elevations the most likely place to trigger a dangerous avalanche would be in steep terrain with a continuous slab layer on top of old unconsolidated snow. Thinner slabs will be more sensitive and can propagate into thicker areas if triggered.

    Near the port, hard and soft slabs up to 8 inches thick overlying a breakable crust were sensitive to human triggers within the last several days.  This problem is limited to isolated steep slopes at elevations below 1700 feet. Users should keep an eye out for larger pockets of slab overlying thin crust on slopes over 35 degrees at low elevations. This situation could produce an avalanche with consequences.  Slabs without the rain crust below will be less sensitive. 

     Old slabs may become sensitive to the new snow load. Storm slab avalanches may have the potential to step down into deeper layers within the top 2 feet of the old snowpack. 

    As slabs and crusts get buried by new snow they will be harder to detect. Pay attention to what the snow feels like under your feet when traveling. Be aware of drum-like sounds, collapsing and/or cracking underneath your feet while traveling today. If you encounter slabs be sure to determine their extent and sensitivity before traveling in steeper terrain. Hand pits/quick-pits/probing are good tools to quickly see if the new snow overlies a slab or crust. 

     

  • Glide Cracks

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    2–3

    The glide avalanche problem continues although we haven't seen any release recently. A good example of the glide crack problem can be observed on Town Mountain at mid to upper elevations. Cracking in this area is widespread and the snow has been observed to be creeping slowly downhill. Other glide cracks have been observed in all zones and elevations but they are most prominent at mid-mountain in the marine zone. Continue to monitor the locations of these features as they are not going away any time soon. They can released unexpectedly with serious consequences. Make a mental note of these features so you will know where they are after they get buried by fresh snow.

Avalanche Discussion

Benign weather over the last several days has allowed for good travel conditions in all of our zones. Observations over our forecast area have revealed some isolated reactivity involving persistent layers in the top 2 feet of the snowpack, but no associated avalanche activity. The sensitivity and likelihood of triggering these layers have been decreasing over the last several days but this may change with the incoming storm. 

Significant snowfall is expected over the next 48 hours for Thompson Pass and higher elevations around Valdez. Today will start with modest accumulations but things should pick up as the day goes on. There is a bit of uncertainty in snowfall amounts today but expect widespread storm slabs in areas that see 6-12 inches of snow. Into tomorrow we will see an increase in precipitation with the potential for up to an additional foot of new snow for higher elevations. The possibility of human-triggered and natural avalanches will be increasing during this time. Expect storm slabs 1-2 feet deep to be sensitive to triggers as snow intensity increases tomorrow. This snow load may increase the sensitivity of the persistent wind slabs we have been observing over the last week. 

Lower elevations up in the port are forecasted to transition to rain as temperatures rise in the next 24 hours.  Rain may reach elevations of 1000-1500 feet before turning back to snow near the end of this storm. Rain and wet snow create small to medium wet loose avalanches near the port.  If temperatures stay cold enough for snow there will be an additional load on the sensitive rain crust below 2000 feet. This would create touchy instabilities especially where there are hard slabs on top of the cust. 

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