Avalanche forecast

East Slopes South

Northwest Avalanche Center
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Avalanche danger

Fri
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Highlights

Persistent slabs remain on the menu in the East South as we transition from warmer to cooler temperatures. Unpredictable wet slabs continue to be the biggest focus, but persistent slabs may still be triggered within dry snow on northerly aspects . Continue to limit exposure to middle and upper elevation slopes steeper than 30 degrees where the risk of deadly avalanches drives enhanced caution.

Avalanche problems

  • Wet Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–3

    Thursday will feel winter-like in the morning and spring-like in the afternoon. However, meltwater continues to move deeper into the snowpack following a week of unusually mild weather and notoriously tricky wet slabs remain a concern. If this meltwater pools on a crust or encounters a weak layer to lubricate, a slab may fail suddenly and without warning. These could be large or even very large and life-threatening. The likelihood of this problem is somewhere between possible and unlikely, but there remains a fair amount of uncertainty and variability depending upon aspect and snow depth. You don't want to be in the wrong place at the wrong time. You're accepting risk if you travel on or under steeper W-S-E aspects, but you can limit your risk by traveling early when surface crusts are firmer and thicker. Once the crusts break down, expect additional meltwater flow to increase the likelihood of slab releases in the afternoon. Be aware of overhead hazard and the terrain you're connected to.  A large natural trigger like cornice fall could trigger a large wet slab avalanche on the slope below.  Stay well out from under cornices and give them a wide berth on ridgelines as they often break further back than you expect. 

    In some areas, wet loose avalanches remain a concern in areas where you find heavy, manky snow. You can test this hazard on a small, steep test slope, but don't underestimate the potential size of a wet loose gaining steam on a steep slope above you.

    (3/16/2024)

    Snowmobilers triggered this avalanche on a southern aspect in the Ahtanum on Saturday, March 16th. It likely failed and ran on the Early February Crust. 

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    2–3

    We've been dealing with persistent problems in the East South much of the season and it appears that these problems may linger longer on the colder, layered, more shaded northerly aspects. Our attention focuses on a layer of surface hoar just above the layer of rounding facets on the Early February Crust (EFC). Moist snow exists near the surface, but the dry, layered snowpack found underneath maintains some concern. These slabs will be unlikely to trigger if you are on top of a crust, but may trend into the possible range if you find dry snow at the surface. Unlike the wet slabs, human triggers will likely be involved. Continue to approach large terrain features with caution and limit your exposure to steep slopes greater than 30 degrees. Whumphs may be your only indication of a problem in your area and you may not be lucky enough to get such a warning signal.

    (3/19/2024)

    A snow profile from a North aspect at 6700ft near Darland Mountain. Only the top 1-1.5ft of the snowpack is moist, with dry snow below that. 

    Photo: Katie Warren

Avalanche Discussion

We're nearing the end of a wet slab cycle following a week of anomalously warm weather. Recent observations highlight the colder, drier and more layered nature of the snowpack on northerly aspects. Time will tell whether sufficiently thick crusts form to bridge these weaker layers. 

NWAC Forecaster Katie Warren was out in the Ahtanum/Darland Mt area on Tuesday.   The prolonged period of sun and warm temperatures had done a number on the lower elevation snowpack and steeper southerly slopes.  Wet snow avalanches from the last few days were not as widespread as in other zones and there were tracks on many slopes in the immediate area.  The snowpack on southerly aspects was wet and moist to the ground, but more supportable than other sunny aspects where you could punch through wet snow to your waist.  Northerly aspects held a colder, more layered snowpack and the early February crust was easy to find about 4' down on a N aspect @ 6700'. 

On Saturday, there was a close call where snowmobilers triggered an avalanche in Ahtanum that failed on deeply buried weak layers.  While we haven't seen any new avalanches on this layer, the structure is there.  The potential for large and destructive avalanches will linger during this extended period of warmth as meltwater moves through the snowpack. Before this warm-up, we had a widespread, persistent slab problem. There was a fatality three weeks ago in Ahtanum Meadows area, and in the neighboring East Central, we saw multiple large human-triggered persistent slab releases last week.  

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