Avalanche forecast

Elkhorns

Wallowa Avalanche Center
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Avalanche danger

Sun
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

Big changes to the snowpack in the form of significant warming suggest a step back in terrain selection.  A rider could likely trigger wet loose avalanches on sunny slopes by mid-day through this evening on steep terrain greater than 35 degrees.  It remains possible to trigger a deeper and more destructive avalanche on several buried persistent weak layers that lurk on shady slopes near and above treeline.  Avoid riding in steep terrain or above terrain traps as the sun and warm temperatures heat the snow surface. 

It is with profound sadness that we report an avalanche fatality that occurred on 3/6 in the Northern Elkhorns. Our backcountry community is small and we understand the tremendous grief many are experiencing. Our thoughts and prayers go out to all affected. An accident report will be forthcoming. A preliminary report can be found below in the forecast discussion.

This forecast is sponsored by  Wallowa County Search and Rescue

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–3

    There are multiple persistent weak layers that we have been tracking in the snowpack.  Some of these layers have the potential to create large deadly avalanches.  These layers have woken back up as the slab of snow that sits above them has gained cohesion.   As temperatures warm, you may be pushed into terrain that is more likely to hold colder and (relatively) drier snow.  The problem is that this is where these weak layers could be lurking.  Careful snowpack evaluation is warranted before committing to slopes greater than 30 degrees in steepness.   Below is a rundown of the persistent weak layers that you should keep your eyes on.  

    Buried Surface Hoar:  There are a few layers of buried surface hoar that we've been tracking.  One was buried on Valentines Day, and has been gaining strength over time and showing less reactivity in snowpack tests.   The other was buried on 2/26 and has been found anywhere from 2-2.5' from the surface.  This layer has shown reactivity in snowpack tests.  The third, closer to the surface is 8-12" deep and has been noted in the Norway Basin area and has also been reactive in snowpack tests.   These layers of Buried Surface Hoar can be found on NW-N-NE aspects above 7,000' in shady and wind-sheltered terrain.  The distribution is spotty, but has been found in the Southern Wallowas, Western Wallowas, and Elkhorn Mountains.  They may be difficult to see in your snowpit wall- so isolate a column and conduct a snowpack test to test their reactivity.  See a recent observation here from Killian Sump of Wallowa Alpine Huts yesterday in Norway Basin.

    2/1 Rain Crust/Facet Layer: The layer that was responsible for the March 6th avalanche fatality was a layer of weak faceted snow that sat above the knife-hard Rain Crust that was buried on February 1st.  This layer can be found 2-4 feet deep in the snowpack and demands respect.  We have all the right ingredients here for an avalanche sandwich.  The Rain Crust is the ideal bed surface, the weak faceted snow that sits around it is the weak layer, and all the snow on top of it is our slab.  

    Weak Snow Near the Ground: The biggest surprise of my day yesterday was just how reactive the old snow near the ground was in a shallower snowpack in the Northern Wallowas.  In an area that had only 4 feet of snow, I got alarming results in all of my snowpack tests at a depth of 3.5' from the surface.  The weak layer was old December faceted snow that sat below a melt freeze crust.  You can check out the observation from yesterday here.  

    How to manage this:   Well, large terrain margins are a good place to start.  If you have uncertainty in the snowpack, then choose more simple terrain.  Shallower snowpack areas are going to be weaker and harbor more places to trigger a slab.  Use your probe to track snowpack depths, and while you are probing you will likely note the depth and thickness of the 2/1 rain crust.  In areas where it is closer to the surface, it is more likely to trigger weak snow that has formed around it.  Avoid rocky convex rollovers that are greater than 35 degrees as these are likely trigger points.  

    With a meaty slab on top of weak snow near the ground, this Extended Column Test propagated on the 17th Tap.  

    Photo: Caleb Merrill

  • Loose Wet

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

    It will be likely to trigger wet loose avalanches today on aspects that are seeing direct sunlight and with temperatures rising into the upper 40's.    The lack of a hard freeze last night at lower and mid-elevations will amplify this problem sooner than what you might expect.  When you step off your machine or are on your skis and you sink into wet snow up to the top of your boot, it's time to scoot!   Last week's snow sits above a melt-freeze crust on solar aspects, and this crust will act as the perfect sliding surface for wet loose avalanches to run on.  The classic precursor signs of wet loose avalanches are roller balls and pinwheels entraining surface snow as it is warmed by the sun and warm temperatures.  This may happen naturally- especially around rocks that are warmed by the sun or as you ski or ride over steeper terrain.  Wet Loose avalanches may become large today and entrain more snow than you might expect.  These avalanches could easily knock you off your feet, and push you over unforgiving terrain or stack debris into terrain traps such as gullies/creek drainages.   Avoid slopes greater than 35 degrees in steepness during the heat of the day.  

    Roller Balls and Pinwheels are the precursors to Wet Loose Avalanches.  Look for these signs and avoid steep terrain that is taking the heat!  This was occurring by 11:00 in the Northern Wallowas yesterday.  

Avalanche Discussion

Just like most people, the snowpack doesn't like rapid change.  The warming temperatures we are experiencing is a big change to the snowpack.  It will most certainly create wet loose avalanches, but the effect it has on some of our deeper persistent weak layers may be less obvious but still significant.  The persistent slab problems that we have will likely not give you obvious signs such as Whumphing/Collapsing or Shooting Cracks in the slab.  The best way to find out more information about the slope scale persistent slab problem is to dig a snowpit.  If you question your ability to assess the problem, simply go recreate in simple terrain less than 30 degrees and out from underneath avalanche paths.  

In addition to the above Avalanche Problems, there are a couple more things to keep on your radar: 

Some very large cornices have been growing all season long and will become weaker with the warming temperatures and could break further back from ridgelines than expected.  Give cornices a wide berth.  

Moderate to Strong North and Northwest Winds last week created wind slabs on East through Southerly aspects.  Most of these wind slabs seem to have relaxed with the warming temperatures, and have not been very reactive in the last couple days.  That being said, there was a report of a skier-triggered D1 windslab yesterday in Norway Basin.  You can use small test slopes to test the reactivity of snow that has been drifted into slabs, or just avoid wind-drifted snow altogether.  

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