Bollettino valanghe

Olympics

Northwest Avalanche Center
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Pericolo valanghe

Sun
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4 · Forte
Limite del bosco
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Sotto il limite
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In sintesi

Very dangerous conditions are expected to develop throughout the day as heavy wet snow and rainfall overload a layered snowpack. High danger and large natural avalanches are expected to continue overnight into Sunday morning. Avoid all slopes where avalanches can start, stop, or run.

Problemi valanghivi

  • Wet Slabs

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

    Heavy rainfall will saturate a previously dry upper snowpack, potentially pooling on crusts and weaknesses in the snowpack formed during the January Drought. Once liquid water pools on these layers, we expect large avalanches in the Hurricane Ridge area and potentially very large avalanches in other parts of the Olympics with deeper snowpacks. Wet slabs are notoriously unpredictable. They typically fail during or after heavy rainfall. The risk for these avalanches really ramps up once heavy rain starts to fall in your terrain, but it would be unwise to enter avalanche terrain on Saturday, given how quickly conditions are expected to change. Avoid all terrain where avalanches can start, stop, or run. Wet avalanches might also just fail as loose wet avalanches such as the one pictured in the gallery below.

    Prior to this rainfall, the risk may be significantly lower.  And while snow may fall at upper elevations, the rain will be the far bigger story here as snow transitions to rain at these elevations.

    Example: A large natural wet avalanche like we expect to see Saturday and Sunday.

    Photo: Rob Pollard

Avalanche Discussion

Variable snow surfaces (a mix of shallow wind slabs and thin surface crusts) overly a dry upper snowpack prior to the atmospheric river bearing down on the Olympics. This variability may still exist early Saturday before rainfall rates increase as the day progresses.

The biggest uncertainty in this forecast is how much rain shadowing the northern Olympics will receive. Currently we expect 1.2" of water equivalent for the Hurricane Ridge area with more than 2" likely over the next 24 hours in the eastern Olympics. Given the discrepancy, it is possible that the northern Olympics will have the avalanche cycle delayed relative to other areas. Much of that water will arrive after 10 AM on Saturday, so expect rapidly deteriorating conditions as the day progresses.

We removed the January Drought Layer (JDL) and associated crust complex as a problem, but we think it could reactivate on Saturday into Sunday. Facets are sandwiched between a series of crusts (1/10 and 1/29) 16-20" below the snow surface on shaded aspects. Rainwater will pool and destroy these weaker snow grains causing large (or very large) slab failures. 

Share your observations with the community and NWAC. Even if you didn't see an avalanche or a snowpack test, your information is incredibly valuable.  Every afternoon, 4-5 NWAC forecasters from around the region meet to discuss the latest snowpack and avalanche observations, and weather forecast to create the next day's avalanche forecast.  We look at information from the public, other snow professionals, and weather station data to round out our picture.  Share early and often!

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