Bollettino valanghe

Continental

Valdez Avalanche Center
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Pericolo valanghe

Alta quota
3 · Marcato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

The avalanche hazard is Considerable above 4000' and decreases with elevation.  Human triggered avalanches 1-2 feet in depth are likely in steep terrain on the lee side of ridges and terrain features.    Shooting cracks in the snow, collapsing and recent avalanche activity are all signs that a slope has the ability to produce an avalanche.  In areas where the snow is unaffected by wind the hazard will be lower.

Problemi valanghivi

  • Storm Slabs

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

    Expect storm slab depths to vary depending upon south wind redistribution and elevation.  From 2500'-4500' expect to find storm snow from the last week in the 10-20 inch range depending upon wind exposure.  In the mid elevations, sensistivity has only been observed in small wind loaded pockets and storm snow is showing signs of bonding well with the rain saturated snow from Thanksgiving.  

     

    Above 4500' rain was not experienced during the Thanksgiving warm up and new snow amounts over the last week are unclear, but could be significantly higher.  Strong southerly winds have accompanied the last 48 hours of moderate snowfall, so we are expecting sensistive pockets 1-3 feet in depth on steep wind loaded northerly aspects.

     

    There is a high amount of uncertainty about depth and sensitivity of high elevation wind loaded slopes , due to a lack of recent field observations from that elevation band.  Therefore a Considerable hazard rating has been issued for upper elevations.  Careful snowpack assesment will be necessary for safe travel in steep high elevation avalanche terrain today.   Pay attention to clues to the direction of previous wind, such as fresh cornice development pointing towards wind loaded slopes and eroded snow surfaces pointing towards the wind direction.  Use terrain progression to get an understanding of the new snows stability before exposing yourself to consequential terrain.

     

    Storm slabs are not a concern below 2500' due to low accumulations falling on a rain saturated snowpack that has refrozen and gained strength.

     

     

     

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–1.5

    Wind direction shifted from SE to NE on Thompson Pass around midnight last night.  As skies clear it is possible that north winds will be stronger than forecasted.  If this happens expect for sensitive wind slabs to develop on SE-NW aspects.  Avoid areas receiving active wind loading on slopes steeper than 32°, especially where terrain traps are present.

Avalanche Discussion

This first avalanche forecast of the season deals with a lot of uncertainty about storm snow depths above 4500' and their sensitivity in wind loaded locations.  The past week of weather produced fairly steady precipitation and winds that where moderate to strong from the south with shifting direction.  This combination would indicate that wind loaded northerly slopes may be reactive to human triggers 1-3 feet in depth.  Watch for signs of wind loaded slopes such as a pillowed snow surface and use small test slopes without consequence to determine sensitivity.

We currently have better focus on the current state of the Mid and Lower elevation snowpacks.  The warm up during Thanksgiving brough rain up to ~4500' . Freezing line slowly descended over the next 72 hours but remained at ~2500' until 11/29.  This warm up/rain event introduced a lot of free water into the snowpack below 2500'.  As temperatures have cooled the snowpack has slowly refrozen and gained strength. 

Between 2500-4500' less of a warm up occurred although a rain crust stil exists from thanksgiving rain with the new snow showing signs of bonding well to this layer.  Below the new snow a strong snowpack has been found with no persistent weak layers yet identified, besides rounding depth hoar at the base of the snowpack.

 

Leave an observation if you see signs of instability, recent avalanche activity or anything else notable.  

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