Bulletin d’avalanche

Continental

Valdez Avalanche Center
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Danger d’avalanche

Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
2 · Modéré
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Points saillants

The avalanche hazard is Moderate at all elevations.  It will be possible to trigger an old wind slab avalanche today in isolated locations where slabs are thinner.    Natural and human triggered wet loose activity may become possible on southerly aspects at low elevations. 

 

 

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Unlikely
    Taille
    1–2

    The avalanche hazard remains largely unchanged from yesterday other than one more day for wind slabs that formed 2/27-3/2 to settle and gain strength.  In many locations wind slabs and stripped surfaces are knife hard, in these locations these very stiff surfaces are unable to bend and crack making avalanche initiation unlikely.  

    Wind slabs may remain reactive to human triggers in isolated locations.  These would be areas where the slab is thinner or softer and a human or a machine's weight can penetrate the layer.  Another consideration would be areas with lots of tracks.  As tracks eat into an area of thinner wind slab it can slowly be weakened.  Human triggered avalanches are possible after many tracks are on a slope.  Once again this will only occur where slabs are thinner or softer and a snowmachine or ski has the ability to penetrate the surface of wind slabs.  This is not the case for most places, as rock hard snow surfaces that are impenetrable to skis or machines are the current norm for the Thompson Pass area.

    A moderate hazard rating has been maintained due to some deep natural avalanches that have occurred over the last week during the outflow.  As well as, a very small chance of a person triggering a wind slab that propagates to a deeper section of slab producing a dangerous hard slab avalanche.  This variety of avalanche is far more dangerous than your typical soft slab as the density and mass of the debris is very likely to injure a person or worse.  The most accurate description of our current hazard level would be Low hazard with isolated pockets of Moderate.

    Avoid areas of wind slab that your skis or machine can penetrate.  Pole probing can be a good test of wind slab strength.  Hand pits are currently an ineffective assessment tool as they will give false unstable results.  It is also wise to avoid large areas of hard slab due to the dangerous outcome of triggering a hard slab even though the likelihood is low.  A trace of snow from March 5 will not affect stability in our forecast area, although higher amounts were reported to the east.  In these areas shallow storm slabs will be possible.

     

    (3/6/2024)

    Typical snow conditions in the Thompson Pass region 3/6 Loveland Basin

    Photo: Joshua McDonald

  • Loose Wet

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–1.5

    As temperatures warm today small wet loose avalanches may occur on southerly aspects below 2000'.  The first places to see this activity would be steep rocky terrain where the sun's angle of incidence is more perpendicular and the dark color of rocks absorb heat and radiate that heat into the surrounding snowpack.  

    Very dense wind affected surfaces will limit the effect that the sun has on the snow today and may prevent this activity entirely.  Watch for signs of the snowpack heating up such as moist snow at the surface or roller balls from steep terrain.  Where these signs are present avoid traveling in steep south facing terrain where even a small wet loose that could knock you off your feet could be an issue.

Avalanche Discussion

We are now in the aftermath stage of the late February North wind event that deeply gouged and reshaped our upper snowpack.  Above 2500' There was  significant snow available for transport with storms from 2/9-10 and 2/20 -22 each depositing around 3 feet of snow.  Below 2500' the 2/20 rain crust limited the snow available for transport to about a foot.  Significant snow available for transport coinciding with a long duration north wind event produced numerous natural avalanches in the D2 range on all aspects with a few deeper D3 hard slab releases as well in Gully 1 NW, and a South aspect near 27 mile ice fall.  All of these avalanches were a direct result of wind loading.

Wind slabs have now had 5 days of settlement time without continued loading and 10 days since the onset of the wind event.  This has allowed slabs to move towards the lower end of the sensitivity and probability scale.  Human triggered avalanches remain possible where slabs are thinner and a person or machine's weight can penetrate them.  These will exist in isolated areas where winds were less severe, but still formed slabs.

Another effect of the rock hard wind affected snow at the surface is that the mid and lower snowpack is now bridged by the strong snow at the surface.  Last week we had a persistent slab and deep slab avalanche problem listed.  These have been removed due to the very low likelihood for a person to affect them.  The Persistent slab problem previously listed was a layer of surface hoar that existed in isolated areas.  In many places, this layer cycled naturally on 2/22 and strong winds have likely gouged deep enough to remove this layer in other places.  This layer is now believed to be very unlikely to encounter due to its very isolated distribution and the high likelihood that wind has either destroyed or bridged it.

The deep slab problem we had listed has been removed as well for the time being.  A significant natural on Tones Temple on 2/24 brought forth questions of a weak layer in our mid-snowpack.  The identification of the layer in question is still unclear, although may relate to a layer of near surface facets that was buried on 2/9 atop a very hard bed surface.  The depth of the potential weak layer along with the bridging effect of wind affected snow at the surface make this problem very unlikely for a person to trigger.  It is expected that if any further activity were to occur at this layer it would be initiated by large weather events or maybe significant cornice or serac fall, not by a person.  

Overall, A deep snowpack with good strength has been observed and reported in many locations.  March 5th brought a trace of new snow to our forecast area that will not affect stability.  To the east of our forecast zone higher amounts have been reported.  In these areas shallow storm slabs will be possible.

Sunny skies and warm temps may allow for small wet loose activity on southerly aspects near the coast in steep rocky terrain.  Very dense wind affected surfaces will take longer for the sun to break down and may prevent this activity entirely.

Glide cracks exist in isolated areas and will be a hazard throughout the season until they fail.  Avoid exposure to glide cracks.

Valdez season snowfall: 249  inches

Valdez March snowfall: 1 inches

Valdez height of snowpack: 69 inches

Thompson Pass season snowfall: 596 inches as of 3/1

46 mile height of snowpack: 72 inches

Régions couvertes