Bollettino valanghe

East Slopes South

Northwest Avalanche Center
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Pericolo valanghe

Tue
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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In sintesi

Continued snowmelt sustains the risk of very large wet avalanches on deeply buried weak layers. These avalanches can occur on any slopes steeper than 30 degrees and without warning signs. Stick to low-consequence terrain until conditions improve.

Problemi valanghivi

  • Wet Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    2–3

    A weak snowpack in the Cascades East South is warming up and destabilizing as meltwater impacts existing weak layers. This process can play out over multiple days, triggering potentially very large and destructive avalanches with little or no warning signs. You don't want to be in the wrong place at the wrong time. Avoid traveling on or near large, steep terrain features. Give yourself large margins of safety from potential runout zones. One of these wet slab avalanches could run further and break wider than you may expect. Remember that wet snow packs a lot of force and a wet slab doesn't take time to gain steam like a wet loose avalanche.  

    The unpredictable nature of wet slabs makes them particularly difficult to manage. While the main precipitation events associated with the warmup occurred 12-48 hours ago, wet slabs can fail up to several days after the precipitation inputs as water percolates through the snowpack. Once the water impacts reaches a weak layer, it melts the fragile grains holding the stiff slab above; and that triggers a wet, heavy, and destructive avalanche. These slabs vary in thickness, so predicting the timing is next to impossible. The warmest temperatures of the week on Monday along with sunshine add another variable. Keep in mind that as water flows through the snowpack, cornices may fail and trigger slabs on the slopes below them, or glides may shear off a smooth bedrock interface. Smaller and more predictable wet loose avalanches may also be widespread on Sunday and could step down to the weak layers of concern.

    Note that at lower elevations, the peak of the wet slab threat has passed, but although it lowers the likelihood of wet loose and wet slab avalanches, they may still occur.

    (1/28/2024)

    An explosives-triggered avalanche at Crystal Mountain that propagated widely while exposing rock and dirt.

    [N 6700' WS-AE-R3-D3-O]

    Photo: Crystal Mountain Pro Patrol

Avalanche Discussion

With scary, hard-to-predict wet avalanches, the message you should remember is that until the snowpack experiences below-freezing temperatures, the potential for very large wet slabs remains. Unfortunately, freezing levels will be between 10500 and 1100 ft on Monday with some sunshine that will accelerate the breakdown of any superficial crusts formed overnight. We suspect the peak of the avalanche activity has already occurred, but the danger remains quite real in the East South.

Katie Warren was in the S. Fork Monatash Creek Drainage on Sunday. She found evidence of recent small wet slabs and fresh wet loose avalanches. A snow pit at 6200 ft on a N aspect revealed propagating test results just above the Solstice Crust. This serves as a reminder that conditions remain reactive in the East South zone. Human-triggered large to very large wet slabs at Mission Ridge and near Stevens Pass serve as very strong reminders that rider-triggered avalanches remain likely. Another rider observed a large natural avalanche near Ahtanum Meadows.

Saturday was also a very active day in nearby zones including the West South where multiple very large wet slabs ran naturally at Crystal Mountain, Mt. Rainier, and Mt. St. Helens.  Consider the consequences of overhead hazards or triggering one of these deadly avalanches when choosing terrain. 

On Friday, an NWAC forecaster was out in Ahtanum Meadows near Darland mountain and found the Solstice crust buried over 3ft deep and the 1/2 surface hoar buried 2-3ft deep in a snow profile. While both layers were gaining strength and rounding, the water moving through the snowpack will continue to push us to the tipping point for avalanches, even on these western edges with a deeper overall snowpack. Further east and north, near Manastash ridge, these layers are closer to the surface. They also found a notably stronger snowpack on southerly aspects versus northerly and easterly.

If you get out, let us know what you see by submitting a public observation!

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