Avalanche forecast

Continental

Valdez Avalanche Center
View on map

Avalanche danger

Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
Open full map
Out of date — this forecast expired 2 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

The avalanche hazard is Moderate above 2000'.  Expect to encounter a diverse range of wind-affected surfaces, including wind slabs. In isolated areas, these wind slabs could be triggered by a person in areas where they are thinner.  The likelihood of natural avalanches occurring is low.

 

 

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    The main avalanche problem today continues to be triggering an old wind slab that formed during the near hurricane force north winds that occurred from 2/27-3/2.  The chances of triggering a wind slab have significantly lowered as time has decreased sensitivity with an increase in stiffness.  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.

    If an avalanche is initiated it is possible that it could propagate into deeper areas of the wind slab resulting in a dangerous hard slab avalanche.  The density of this debris is more likely to cause injury or worse if you are involved.  Hard slab avalanches may be able to step down to deeper layers in our snowpack where failure occurred naturally during the 2/22-24 avalanche cycle.  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 not currently an effective assesment 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 yesterday will not effect stability.

    Current typical snow surfaces consist of a mix of wind affected snow.  3/2  mid elevation East Francis

    Photo: Gareth Brown

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 4 days of settlement time without continued loading and 9 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 P 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-lower snowpack.  The identification of the layer in question is still unclear.  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 and structure has been observed and reported in many locations.

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

Regions covered