Bollettino valanghe

Stevens Pass

Northwest Avalanche Center
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Pericolo valanghe

Tue
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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Non aggiornato — questo bollettino è scaduto 2 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Steer around wind-drifted features and pillows on steep slopes.  You can trigger avalanches in recently wind-deposited snow, but there's a very small chance that you might trigger dangerously deep avalanches on older weak layers.  With the uncertainty of triggering deeper avalanches at upper elevations, avoid all steep slopes and consider steering around lower angle terrain beneath steep slopes where an overhead avalanche could run down. 

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    You're most likely to trigger avalanches where the wind drifted the snow into stiffer wind slabs.  Look and feel for signs of drifting, which may be newer deposits, or up to 48 hours old. You might see long, shooting cracks, or just feel slightly stiffer snow, although it could be very subtle. Use clues like searching beneath cornices and around outcroppings.

    Steer around wind-loaded features and slopes over 35° at middle elevations. You can test the recently accumulated and drifted snow on inconsequential, small test slopes before traveling in steep terrain. However, this isn't a sound strategy at upper elevations. There, conditions are doubly dangerous as there's a chance of triggering very large and destructive avalanches on deeper layers. See more below.

    With all the recent snow, be aware of falling in treewells and keep your partners in sight.

    Example photo: Soft subtle wind slab avalanches may occur on Monday. There's a chance they could be deeper as well. 

    Photo: Matt Primomo

  • Deep Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    2.5–3

    Deep persistent slab avalanches can be very dangerous, difficult to predict, and can give little warning as to when you're going to trigger one. The best way to manage them is to avoid avalanche terrain where the weak structure exists. Stay off of and far away from steep avalanche paths above about 6,000ft. Avoid traveling in areas with complex, overlapping avalanche paths. If you trigger one of these avalanche, it will be very surprising, and may propagate widely across terrain features, and break in surprising ways. 

    Heavy snow and wind loading from the last week stressed a weak snowpack structure. At about  6,000ft and higher, avalanches could break on weak layers. These weak layers consist of facets, and where we've dug, the layer has mainly been sitting just above a crust. This weak layer is mainly 4-6 feet below the surface, so it might be very difficult for a human to trigger an avalanche on it, although it's not out of the question.  Right now there's enough uncertainty that it's best to avoid all slopes greater than 30°  at upper elevations. You may find two weak layers, the February 24th layer and the early February crust within a foot of each other. Failures might occur near either of those crust/facet combos. Now that the snowpack has had some time to adjust, it's becoming more difficult to trigger these avalanches near the Cascade Crest. In the eastern portion of the zone, the structure is weaker, and avalanches may be easier to trigger.

    (3/3/2024)

    A natural D2.5 avalanche on Jim Hill that likely failed Feb 28-29. The failure occurred on weak 1mm facets above the Early February Crust. The crown was about a meter (3ft) deep. 

    Photo: Matt Primomo

Avalanche Discussion

An additional couple inches of snow Sunday night with light to moderate SW winds could redistribute snow into soft new slabs. At mid and lower elevations, a bit of sun shining on steep southerly slopes may have resulted in a slight surface crust forming. Since the 24th, the Stevens Pass area has received about 5" of water equivalent, and the snowpack gained 3-4 feet. 

At Skyline on Friday, forecasters found the early February crust not to be an issue for triggering avalanches on south-facing slopes around 5000ft. However, if triggered, a crust/weak layer, just below the February 24th interface showed a high potential for propagation.  A forecaster on Sunday found a D2.5 (large) avalanche on Jim Hill at 6,200ft, NE. It likely failed on Feb 28-29, and the failure was on weak, faceted snow above the Early February Crust. I went to Big Chief on Sunday and dug several pits on different aspects around 5700ft. I found inconsistent results, yet both facets above the Early February Crust and the 2/24 layer were noted and produced test results (compression, deep tap moderate-hard) in some of the pits. 

Your avalanche, snowpack, or weather observations are extremely valuable to the avalanche community. Help create a more accurate avalanche forecast by submitting your observations here. 

 

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