Lawinenlagebericht

West Slopes South

Northwest Avalanche Center
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Lawinengefahr

Tue
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
2 · Mässig
Open full map
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Kernpunkte

Unusual weather often leads to unusual avalanches, and we’ve had a number of those in the West South recently. You should continue to be suspect of any feature over 35 degrees, despite the drop in hazard level. Keep an eye out for your red flag signs of instability and consider the consequences of being wrong before you go jumping into bigger terrain.

Lawinenprobleme

  • Storm Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1.5–2.5

    Even though the recent storm snow started consolidating into a more cohesive slab in many areas on Sunday, there may still be storm-related issues you could run into on Monday. Using uptrack tests, hand shears, or small test slopes while you travel can give you clues about the likelihood of a slab failing and how deep a potential avalanche could be. Bullseye information such as recent avalanches, shooting cracks, or whumpfing collapses should drive you into more conservative terrain. Be leery of steeper slopes, convex rollovers, or wind-loaded pockets where triggering an avalanche could be more likely. 

    Additionally, the presence of weak grains at the base of the recent storm snow could produce surprising avalanches in some areas. If you are unlucky and trigger an avalanche on this layer, it could break above you or wrap around terrain features. You can take a look in the snow for a thin gray line or feather-like snow grains at the depth where you see blocks failing easily in your tests to help identify this tricky problem. When in doubt, stick to terrain under 35 degrees with plenty of natural anchors.

    (12/10/2022)

    A skier triggered slab in the White Pass backcountry believed to have failed on the 12/8 surface hoar layer. This avalanche was 150 feet wide and it's crown was as deep as 2.5 feet. [NNE 6700' HS-ASc-D2-R2-O]

    Photo: White Pass Pro Patrol

Avalanche Discussion

Here’s a bit of a weekend recap as we transition to high pressure for the upcoming standard work week.

Friday: NWAC forecasters identify buried surface hoar (12/8 interface) on all aspects at Mount Rainier. Avalanche professionals in the Crystal Mountain backcountry confirm its existence in the Pickhandle Basin area. No other confirmation is made within the zone, but it is also identified in the Mount Hood, Olympics, and Stevens Pass zones. The depth of this layer is generally 10 inches below the surface. A potent storm starts to roll in Friday afternoon headed directly for the West South zone and continues through the night.

Saturday: The storm rages on in the morning hours. All areas of the zone pick up significant snowfall totals with some close to 1.5 feet. The 12/8 layer is now 1.5-2 feet deep in areas not affected by wind. Crystal Mountain Pro Patrol consistently gets 1-2 foot crowns during their avalanche mitigation work. One triggered avalanche is close to 2.5 feet deep and ran close to full path, growing very large. At White Pass, a skier triggers a hard slab avalanche believed to have failed on the 12/8 interface. The crown is up to 2.5 feet deep and 150 feet wide. The skier gets caught and carried but is not injured. Small natural Wind Slabs are observed in the Crystal backcountry. The 12/8 buried surface hoar is found at Snoqualmie Pass.

Sunday: We get a public observation from Mount Rainier of a natural avalanche that surely looks like it failed on buried surface hoar during the storm. The slide ran a far distance, hitting a road that is popular with snowshoers, walkers, and cross-country skiers. Across the valley, Crystal Mountain Pro Patrol triggers a 3 foot deep, 60 foot wide slab on the 11/22 facets (remember those?). Patrollers also reported getting sudden collapses as they traveled doing their mitigation work. Avalanche professionals in the Crystal backcountry and at White Pass report noticing wind effect, but no new avalanches.

So as you can see, it's been an interesting couple of days around the West South. We currently don’t have any observations from Mount St. Helens, where the bulk of the storm hit. Looking at the neighboring Mount Hood zone, similar persistent-like avalanches are being reported. If you plan on traveling to Mount St. Helens or Mt. Adams, you may want to check out the Hood forecast as well.

Despite all this information, I’m sure there are plenty of folks who went to play in the mountains this weekend and didn’t see any signs of instability. That information is being weighed as well and helps us to drop the hazard level. However, there are definitely some unusual and concerning red flag avalanches within the zone that should be part of your decision-making process going forward. You may want to continue to travel as if the hazard is Considerable even though the likelihood of triggering an avalanche has decreased. You could be out all day and not see a thing, but then get unlucky and find a pocket of weak snow that ruins your season, or worse.

Do you have some information that can help contribute to this narrative in one way or the other? Submit an observation.

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