Bulletin d’avalanche

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Wallowa Avalanche Center
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Danger d’avalanche

Fri
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
3 · Marqué
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Points saillants

Expected rain on snow today will increase the chances of triggering a wet loose avalanche in elevations up to 8,000'.   It remains possible to trigger a deeper slab avalanche up to 8' thick failing on one of several persistent weak layers deeper in the snowpack, especially as rain on snow may increase the stress on several persistent weak layers in the snowpack.   If you start to see the upper snowpack lose cohesion from rain on snow, recreate in terrain less than 30 degrees.

This forecast is sponsored by The Wallowa County Gamblers Snowmobile Club.  

Problèmes avalancheux

  • Loose Wet

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

    Freezing levels could climb to almost 8,000' in the Blue Mountains today.  Up to .25" of rain could fall on new snow, likely creating wet loose avalanches.  Look for lack of cohesion in the upper snowpack, with rollerballs and pinwheels being a telltale sign of wet loose avalanches.  Avoid riding on slopes that are above terrain traps such as gullies, cliffs, or dense trees where even a small wet loose avalanche could have higher consequences.  

    Pinwheels and Rollerballs from warming temperatures or rain on snow events are telltale signs of the wet loose avalanche problem. 

    Photo: Gallatin NF Avalanche Center

  • Deep Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–3

    It remains possible to trigger a deeper and very large avalanche on weak snow that is buried 2-3' in the snowpack.  The Christmas Rain Crust is the likely culprit in this scenario and is more likely where you find the rain crust to be a crust/facet sandwhich where weak and uncohesive snow is layered between two harder crusts.  Spotty distribution of surface hoar buried 1-3 feet has also been reported throughout the northern and southern wallowa forecast zones and have shown reaction in snowpack tests and recently remotely triggered avalanches.  See recent observations here.  The lower likelihood, but higher consequence scenario is triggering a large slab avalanche either as a wind slab or slab avalanche failing on one of these layers, which could add enough weight to a slope and ultimately step down into weak sugar snow near the ground.  This is more likely in areas that hold a shallower snowpack- think areas in the upper elevations where wind has continually stripped snow, rocky areas that are mid slope, or lower elevations that have less than 4 feet of snow on the ground.  As you travel through the mountains today, it is recommended to track snowpack depths with your probe and feel for the depth and thickness of the Christmas rain crust.  If contemplating riding any slope steeper than 30 degrees, careful snowpack evaluation remains critical to look for this weak snowpack structure.  Play the long game- remain patient as our snowpack gains strength over time.  Check out the video below that shows our evaluation of this problem through several snowpack tests yesterday in the Northern Wallowas.  

Avalanche Discussion

The Milk Shakes snotel site has recieved 9" of new snow with 1" of snow water equivelant since monday 1/9/23.  Strong winds out of the south have created a fresh round of wind slabs over the last few days on leeward ridgelines and cross loaded mid slope terrain features.   While warmer temperatures overnight and climbing freezing levels will perhaps make the windslab problem less likely today, a forecasted rain on snow event up to 8,000' will increase the chances for wet loose avalanches.  These should be pretty predictable- if you step out of your boards or off your machine and sink up to your boot tops, wet loose avalanches are likely in terrain steeper than 35 degrees.  Avoid slopes greater than 35 degrees (especially where they are above terrain traps) when you start to see pinwheels and rollerballs. 

The message stays the same as it has been for the last week.  Avoid wind loaded slopes near treeline and above treeline.  Avoid cross loaded mid slope terrain features, and keep your slope angles less than 30 degrees to decrease your chances of triggering a large to very large avalanche.  Over the last week, numerous human triggered avalanches have been triggered in the Southern Wallowas on wind loaded terrain features and in lower elevation areas that harbor spotty distribution of buried surface hoar.   It remains more likely to trigger a slab avalanche 1-3' thick where the Christmas rain crust is thinner and holds weak uncohesive snow around it.  While we haven't seen any avalanches running on the weak sugar snow near the ground since the avalanche in the Northern Wallowas on 12/30, snowpack tests and overall weak snowpack structure indicate that they are still possible.  We haven't had enough of a load in the form of snowfall amounts to overload the structure naturally.   We would still like to see another couple significant loading events (1"-2" of snow water equivelent) to naturally test the snowpack.  Don't let yourself or your riding partners be the additional weight that could tip the balance of this house of cards.  Stay the course- avoid consequential terrain above terrain traps, keep your eyes on your partners while only committing one person on a slope at a time, regroup out of runout zones from overhead or adjacent avalanche paths.  If uncertainty exists in your mind as to whether weak snowpack structure exists in the area you find yourself, use wide terrain margins and lower slope angles to hedge your bets.  

We have been receiving lots of great observations from around the forecast area lately.  Thank you!  It is extremely helpful to help us build these avalanche forecast products.  Keep them coming!  Submit an observation here.  

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