Avalanche forecast

West Slopes Central

Northwest Avalanche Center
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Avalanche danger

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Out of date — this forecast expired 2 years ago.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

Highlights

Bypass steep, complex terrain. Navigate towards planar slopes with shallower angles to reduce the risk of triggering a large avalanche.  Look for and avoid fresh slabs of wind drifted if you get up to higher elevations.

A snow immersion accident resulting in a fatality occurred in backcountry terrain on Wednesday. Keep your partners in sight at all times. Stay close enough to help them if they get buried in a tree well or some other deep snow hazard

 

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–1.5

    You are more likely to find fresh and reactive wind slabs the closer you get to Snoqualmie and Stevens Pass. While wind speeds were light to the north, winds strong enough to transport snow were observed at the passes.

    Textured or scoured snow surfaces, cornices, and wind lips will point towards slopes holding freshly wind drifted snow. Track changes in snow stiffness and use simple tests like hand shears and slope tests to figure out if you could have a run-in with a fresh wind slab.

    (11/27/2024)

    Shooting cracks are indicators of wind slab instability.

    Photo: Payton Schiff

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    2–2.5

    The  likelihood of triggering a large, widely propagating, or surprising avalanche is lowering. That being said, poor snowpack structure still exists with faceted snow lurking 2-4’ below the surface. 

    If you were to trigger one of these avalanches it would be . . . 

    • Where there is less new snow over the faceted layer like in wind scoured areas  - possibly easier to trigger
    • On very unsupported slopes like steep convex rolls or terrain above cliffs - more stress at the slab-weak layer interface
    • In less traveled terrain where there is less information about stability
    • If you put down a big load on a slope like multiple snowmobiles or a big group of people 

    Risk tolerance will probably determine what kind of terrain you get into this weekend. Avoid steep slopes if you want to be absolutely sure you won’t trigger an avalanche. If you decide steeper terrain is on the menu, stick to planar, moderately angled terrain with no consequences in the runout below like rocks, cliffs, gullies, or other terrain traps. If you are unfortunate enough to trigger one, at least there will be a better chance you won’t get hurt. 

    (12/6/2022)

    This large, human-triggered avalanche failed at a layer of faceted snow. While much of the surrounding terrain was quite tracked up with no results, this steep, unsupported slope still produced an avalanche. Austin Pass/West North, northwest aspect at 4700'.

    Photo: Matt Lubar and Phil Straub

Avalanche Discussion

On Friday, many loose snow avalanches up to D1.5 in size were observed in some neighboring forecast zones. While quite a few were from the day before, continued traffic in steep terrain along with sun-warmed cliffs and trees produced another round. If you descend steep terrain, stay alert to snow moving with you. If we have any sun this weekend, look for additional loose snow avalanches below cliffs and other terrain warming in the sun and shedding snow onto slopes below.

On average there's three or more feet of right-side-up snow over the old snow surface buried on January 30th. This snow sits directly on crust in terrain that saw strong sun and warming from January 26th through 29th. On more shaded slopes, the new-ish snow lies over a layer of faceted snow over a crust - now decomposing - that formed closer to the new year.  More faceted snow is found below these crusts on all aspects. 

The snowpack set up along the west slope of the Cascades is similar but avalanche activity has played out differently depending on forecast zone. An observation from the Mt Loop confirmed natural avalanche activity that likely occurred earlier in the week or last weekend. Stevens Pass has seen minimal avalanche activity while a fresh natural avalanche was reported from Snoqualmie Pass on Thursday. West North saw a flurry of natural avalanches over the weekend and also a human-triggered avalanche on Sunday that resulted in a burial (and thankfully a successful recovery) . But avalanche activity has tapered there despite plenty of folks pushing into steep terrain. 

Minimal snowpack information is available for West Central. Don't ignore obvious signs of instability like whumphing or shooting cracks, but don't think the absence of these signs means you are good to go. Send in an observation if you get out there in the coming days.

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