Lawinenlagebericht

East Slopes North

Northwest Avalanche Center
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Lawinengefahr

Sun
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
2 · Mässig
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Kernpunkte

Upper elevation northerly aspects with previously dry snow may become dangerous where new snow and a touch of wind loads existing weak layers .  In these areas, choose slopes less than 30 degrees. Where new snow overlies a crust, use simple slope tests and hand shears to identify steep slopes that might take you for a short ride.

Lawinenprobleme

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    2–3

    Crusts will limit persistent concerns to upper elevation NW-N-NE aspects. Specifically, any slopes where you have dry snow underlying the fresh storm snow. While this alone makes it possible to trigger a persistent slabs. Wind drifting of the anticipated 6-8" of fresh snow could push the risk into the dangerous category in areas where you find drifts more than 8" deep.  Any avalanche could break widely across terrain features and would be difficult to survive if caught. To mitigate the risk of this hazard, track the distribution of crusts before you expose yourself to upper-elevation northerly slopes, or connected terrain. Put a terrain buffer between your group and large start zones or complex avalanche paths above 6,500ft. Use extra caution when you find less than 5 feet of snow, such as shallower areas near rocks. Facets buried at the beginning of February exist over a crust 2-4 feet below the surface. If the snowpack conditions are suspect, give yourself a sound safety margin by choosing slopes 30 degrees or less, where the slab is unlikely to propagate across the slope.  

    Although we suspect that some snowpack have water tricking through them, we think that most have sufficient crust formation by Saturday that slabs are unlikely. If you do find areas of manky, wet snow, the recently forecast wet slabs may still be in play. In this case, the above travel advice extends onto affected aspects.

    (3/15/2024)

    This crown from Azurite Peak highlights the type of big, alpine terrain where the potential for very large human-triggered or cornice-triggered avalanches remains.

    Photo: Willie Webster

  • Storm Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1

    With 6-8" of expected storm snow, storm slabs will be mostly small and manageable. However, they could get you into trouble in the following areas: (1) Any triggered slab on upper elevation north-facing aspects drastically increases the likelihood of waking up the persistent layer. (2) Areas where the winds have drifted the snow slightly deeper - use your powers of observation to anticipate drifts on atypical aspects given the easterly and variable winds; and (3) in areas where the snow is poorly bonded to the existing crust or a potentially weakening dry snow interface - hand shears and small test slopes can help you identify the problem before you engage with consequential terrain; and (4) slopes above a terrain trap such as a creek, gulley, or hole where even a small avalanche can bury you.

    (3/5/2023)

    Example: Storm slab releasing on a crust.

    Photo: Willie Webster

Avalanche Discussion

A refreezing upper snowpack (at least at middle and upper elevations) will do much to limit wet slab concerns. However, the new storm snow will accentuate hazards on aspects that stayed colder throughout the recent warmup. This narrows the focus of our persistent concerns to areas without a crust, where a human is more likely to trigger a potentially very large avalanche.  The East North has finally enjoyed multiple nights with good refreezes at middle and upper elevations.

From March 14th through 6 AM on March 20th, the Washington Pass Upper station remained above freezing with shallow refreezes on many aspects. Particularly during the early phase of the warm spell observers reported significant avalanche activity that has us keeping our eye on this layer moving forward.

Since the 14th, observers reported natural wet avalanches on steep, sunny slopes up to size D2. The most recent large slab avalanche was reported on Sunday in Willow Creek, WNW, 7,200ft had likely released at some point in the previous 48 hours. This occurred on an unsupported slope, possibly due to snow shedding from overhead cliffs, and it likely ran on either a weak interface from March 9th or layers buried in February.

On the 16th, an NWAC observer got an aerial overview of recent avalanche activity and cataloged numerous large to very large slab and wet avalanches. We suspect many of these slab avalanches ran on the March 9th interface, while the deeper slides were likely on facets above the Jan 31st crust. Several small wind slab avalanches and numerous large to very large persistent slab avalanches were also noted in the second half of last week (see photos below).  From 3/9-12, the Harts Pass Snotel has picked up about 1.8" of water, all falling as snow at mid and upper elevations. On March 5th, forecasters visited the site of a remotely triggered (D3) avalanche on Kangaroo Ridge, which ran on a layer of facets buried in mid-February, just above the Jan 31st crust. 

The cornice hazard decreases with the cooling temperatures, but continue to be mindful of the potential for cornices to sag and fail on slopes overhead. When traveling on ridges, keep plenty of distance from the edge and ensure you're not traveling on overhung snow. Cornice falls are difficult to predict and they often overhang the slopes where we have the most avalanche concerns. 

Lower elevations and sun-exposed aspects may be significantly melted back. Prepare for rocks, stumps, and frozen avalanche debris that may be shallowly covered by fresh snow or fully exposed.

Snowpack information is limited outside of the Highway 20 corridor and Harts Pass. Let us know what you find if you get out into the backcountry!

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