Bollettino valanghe

East Slopes North

Northwest Avalanche Center
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Pericolo valanghe

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

Fresh wind slabs will increase both in size and likelihood later in the day and further Saturday evening as a storm blows through the region.  In the eastern part of the zone with shallower snow depths, the buried surface hoar layer in the upper snowpack is likely easier to trigger than the Washington Pass area.  If you encounter whumpfing or rolling collapses, step back to simpler lower angled terrain without overhead exposure. 

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely
    Dimensione
    1.5–2.5

    While there are several weak layers to talk about, the one closest to the surface that we're targeting is the Jan 5th buried surface hoar layer.  In the Washington Pass area, this layer is about ~2' below the snow surface and hasn't been involved in any human triggered avalanches since 1/12.  Further east, observers on 1/19 in the Tiffany Mt area saw recent avalanches on this layer, shooting cracks and felt collapses, indicating that triggering an avalanche is far more likely in this portion of the zone. 

    Deeper weak layers involved in the very large Liberty Bowl/Blue L. Peak avalanche are detailed below and worth tracking when and if we return to an active storm pattern or other significant new snowpack stressors. 

    Depending on where you traveling in this spacious zone we call East North, you'll need to adjust your travel practices. Digging snow pits and looking for propagating test results can help you identify these weak layers in the top 2-3 feet of the snowpack in western portions.  Further east, you need to have a more conservative mindset.  Put plenty of space between where you travel and large unsupported start zones and shallow areas near rocks and cliffs.  Watch for long shooting cracks and audible collapses as you travel.  Persistent slab avalanches often surprise travelers, breaking further across the slope and around terrain features and/or from lower angled terrain.

    (1/19/2023)

    Crown lines from a recent Avalanche near Clark Peak (Tiffany Mt area). Probably released on buried surface hoar. (N 6900', HS-N-D2-R2-O)

    Photo: Willie Webster

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–1.5

    New snow and wind will form fresh wind slabs near and below ridgelines on Saturday.  Friday's warm temperatures and sunshine will likely limit the amount of old snow that's available for transport. 

    Steer around steep lee slopes where you find smooth pillow-like drifts and the bases of steep cliffs where wind-blown snow likes to collect.  Blowing snow and building cornices will give you clues as to which aspects are being loaded.  You can choose lower-angled entrances off of ridgelines to avoid triggering a wind slab in the new snow.  

    Visual clues such as newly formed cornices or pillow-like piles can help you identify which slopes to steer around. If you see red flag signs like shooting cracks or new avalanches, choose lower angled and more sheltered terrain. 

    If the storm exceeds snowfall predictions, larger and more consequential avalanches will be possible on lee slopes.  Monitor conditions during the day and step back to lower-angled and more sheltered terrain if necessary. 

    (1/5/2023)

    Cracks shoot through wind-drifted slabs just below a ridge. 

    Photo: Frank Clements

Avalanche Discussion

Friday was a beautiful day in the mountains.  Warm air aloft punched in some above freezing temperatures at higher elevation stations near and east of the Cascade crest including Washington Pass, Lyman Lake and Dirty face Mt.  Forecaster Katie Warren observed several wet loose avalanches on steep southerly aspects including one large one on Whistler Mt.  Winds were generally light with little snow moving along ridgelines. 

Professional observer Willie Webster traveled to the Tiffany Mt area on Thursday and found what is likely the Jan 5th surface hoar layer about a foot down.  This layer produced some whumps and indicated propagation was likely in snowpack tests (check out the video below).  Small wind slabs could be easily triggered below ridgelines on test slopes. 

Wednesday, NWAC observers went to take a look at the very large slide that occurred in Liberty Bowl/Blue L Pk. While a known failure date is not confirmed, it likely occurred between 1/13 and 1/14. Upon investigation, it was determined that the upper crown failed on the Christmas Crust, while the step down was to the mid-November facets (11/22).  A crown depth of 5-8 feet was measured.  This avalanche highlights the spatial variability with deeper weaknesses in the snowpack that come out in different ways during large-scale loading events. 

On Monday, observers at 6,200ft, NW in the Hairpin valley reported sudden and propagating test results on the Jan 5th buried surface hoar, 2 feet (70cm) below the surface. The results were very hard (beyond the limits of standard tests) and the surface hoar was small and rounding (0.5mm). 

A significant cycle of wet avalanches occurred last week (1/13 and 1/14) in the lowland hills with some avalanches gouging to the ground. Check out the media reel below and our observation platform to see more media of the impressive slides. 

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