Bollettino valanghe

West Slopes Central

Northwest Avalanche Center
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Pericolo valanghe

Sun
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3 · Marcato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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In sintesi

Expect a mild, almost dry morning with strong winds and increasing snowfall in the afternoon.  Fresh slabs of wind drifted snow will be found near and above treeline by the afternoon. Wet loose, glide, and cornice fall avalanches are becoming less likely - but it's been too warm for too long with too much rain for the threat to pass quickly. Keep track of the terrain ahead of you and also what is overhead. Another wet, wind, warm storm is forecast for Sunday.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–2

    You could find two different types of slab avalanches on Saturday. Renewed snowfall and strong winds will likely build fresh slabs, especially in the afternoon. These will be smaller, shallower, and easy to identify. They will also be more common in wind loaded terrain features As snow levels drop you will start finding them at elevations that saw only rain through Friday. 

    At elevations well above the rain-snow line of 5000,’ there should 1'-2' thick slabs of dense new snow. These quickly become stubborn to trigger with mild temperatures, but can still release on unsupported terrain features or with a large load like a smaller avalanche or cornice fall. The easiest solution to avoid these is to skip traveling on or directly under large open slopes at upper elevations.

    Cracks in the new snow are trying to tell you to stay off steep slopes. Shallow, unstable slabs could form through the day with sustained winds.

  • Glide Cracks

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    Most mid-elevation weather stations will have recorded 36-48 hours of near or above freezing temperatures by Saturday morning, along with an inch or so of rain below 4500'-5000’. Wet avalanche activity will become less likely with a cooling trend and lighter precipitation. Glide slabs and cornices that started to come unglued during the storm could still fall down in the next few days. Limit travel directly under glide cracks or sagging cornices. Also be on the lookout for steep, snowy cliffs that show signs instability like rollerballs or snow shedding off of rocks and trees.

    Example of a large glide avalanche on rock slab (just left of center) below Huntoon Point last winter.  Note hanging blocks, hangfire and a sagging cornice all surrounding avalanche release area.

Avalanche Discussion

Precipitation totals across West Central weather stations averaged around 1" for the latest storm with the rain-snow line hovering around 4500'-5000'. The White Chuck Tripod saw steady above freezing temperatures and a loss of 4" of overall snow height. This means it probably rained for the duration of the storm in the mountains east of Darrington.

The biggest precipitation totals in the North Cascades were logged at Heather Meadows up in West North. That station picked up 2.5" of precipitation with roughly 6" of wet new snow at 5000'. The remainder of that zone had precip totals on par with West Central. With high danger and poor visibility, avalanche observations in West North were mostly limited to ski area control work that produced wet and slab avalanches up to D2 in size.  One backcountry team did manage to get out in the Baker BC Thursday and found this.

Less precipitation was recorded in Stevens and Snoqualmie Pass (0.4"-0.5") and a few folks actually got out in those zones. A team in the Alpental Valley found widespread wet loose avalanche activity. Most avalanches initiated in steep rocky terrain but human triggered slides were easy enough to get going as well. Glide cracks were also observed as opening up with the rain and continued warm temperatures.

If you get out in the mountains Saturday let us know what you see out there!

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