Bollettino valanghe

East Slopes North

Northwest Avalanche Center
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Pericolo valanghe

Fri
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

Strong winds and a trickle in of new snow could create soft, shallow windslabs at upper elevations. Chances are low for triggering hard persistent slabs, but these continue to dictate where one can safely travel. Be careful treading into complex or unsupported terrain at mid and upper elevations on the north half of the compass, especially with larger triggers such as snowmobiles or the combined weight of a group of people. 

Problemi valanghivi

  • Persistent Slabs

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

    You may still be able to trigger large persistent slab avalanches on slopes 35 degrees and steeper. Avoid large, rocky, unsupported avalanche paths, especially on the north half of the compass. Put a large buffer of terrain between where you travel and large start zones. Minimize your exposure to avalanche terrain and look for safe locations to stop and regroup. Keep in mind potential for cornice falls while the wind blows, these could trigger larger slab avalanches on unsuspecting travelers below. 

    "Red flag" indicators of persistent slabs are whumphing collapses and snowpack tests that pop or drop suddenly. Avoidance of large, complex terrain is really the only way to be sure to stay safe, even though chances of triggering one of these may be low. You can dig down and find the culprit, the late-January weak layer can be found 1-2 feet below the surface.  In many areas, this layer is a combination of weak sugar-like facets sandwiched between two buried crusts.Sometimes you'll find weaker snow or old surface hoar above the upper crust. The weak layers are deepest near and west of the Cascade crest and in wind deposited zones. In the eastern part of the zone and in wind scoured areas, the crusts may be found near the surface.

    (2/5/2022)

    A skier triggered avalanche near Maple Pass. Three people were caught, one was carried over 400ft with no injuries. E, 6,600ft

    Photo: NWAC public obs

Avalanche Discussion

Strong NW winds and some snow may make for a wintry day in the high country on Thursday. As always, the weather forecast is not a sure bet. If you observe steady snowfall and strong winds expect that a real wind slab avalanche problem could develop. Observers have been finding up to 6" near and west of the Cascade crest.  Gusty winds and a trickle in of new snow may create drifts near ridgelines and in open-exposed alpine terrain. There could be enough new snow and wind to form shallow windslabs in those areas. Be on the lookout for these as you gain elevation, and check for cracking in the snow. Test slopes can be a good way to evaluate shallow, new snow instabilities, although it is the persistent slab that really dictates where one can safely travel in the zone. 

On Monday, forecasters targeted the late January weak layer on Silverstar and Upper Cutthroat. The one thing in common is that most tests produced sudden collapse results. On Wednesday observers found sudden collapse test results with compression tests in Fisher Creek. In general, shaded, northerly aspects are still showing the most potential for human triggered avalanches where the crust-facet sandwich is most defined and weakest. The most recent natural avalanche on this layer was a D1.5 on a rocky, unsupported east aspect, near treeline on Porcupine Peak (see photo). Last week, observers noted a cornice fall that triggered a large wind slab avalanche in rocky north-facing terrain. On  February 5th, a notable avalanche was triggered near Maple Pass on an east aspect, near treeline. The slide likely occurred on the late January PWL and involved 3 people, carrying one over 400ft. Widespread whumpfing, rolling collapses, and remote triggering of avalanches were all common last week, though these direct signs of instability have become less frequent in recent days. The recent warm temperatures appear to have helped the snowpack and late January weak layer gain strength. 

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