Bollettino valanghe

Olympics

Northwest Avalanche Center
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Pericolo valanghe

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

An incoming storm will increase the avalanche danger late tonight and Sunday.  Avoid all wind-loaded slopes with freshly drifted snow and make sure to give cornices a healthy buffer along ridgelines.  Steer around convex rollovers and unsupported slopes in wind sheltered terrain where you can trigger a storm slab avalanche. 

Problemi valanghivi

  • Wind Slabs

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

    It looks like we are in for another round of wind and snow late tonight through Sunday.  Strong southerly winds will load the same lee aspects that were impacted on Thursday night and Friday morning.  Avoid wind loaded slopes steeper than 35 degrees, especially open slopes above treeline where avalanches are likely to be deeper and more consequential.  You're most likely to encounter firmer wind affected snow on W-N-E aspects in the Hurricane Ridge area as winds continue to scour southerly aspects and ridgelines.   Seek out lower angle and/or treed terrain on Sunday. 

    Use care along ridgelines where cornices are growing larger during this storm cycle. Make sure there's a healthy buffer between you and where cornices may break.   A group at Stevens Pass had a scary encounter last week with a cornice release during poor visibility.   A cornice release would likely trigger an avalanche on the slope below.   

    Identifying fresh cornices will help you determine which aspects were recently wind loaded. 

  • Storm Slabs

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

    Steer around convex rollovers and steep unsupported slopes where you can trigger a storm slab avalanche in the new snow.  You can use small inconsequential test slopes to gauge the likelihood of triggering a storm slab avalanche before committing to steeper slopes.  Pay attention to snowfall rates; if new snow is accumulating at more than 1"/hr over several hours you are likely to trigger an avalanche on any slope steeper than 35 degrees.  Storm slabs may break on storm layers or in isolated areas down to the 3/4 crust.  The 3/4 crust should be anywhere from 1.5-2.5' below the surface in wind-sheltered areas.   

     

    Ex: Human-triggered storm slab avalanche on an open slope below treeline.

Avalanche Discussion

Another 5-10" of snow with strong to even extreme winds are forecast for the Hurricane Ridge area through Sunday afternoon with winds peaking early Sunday morning.   This is coming on the heels of 20"+ of new snow from Thursday afternoon through Saturday afternoon.  Prior to these storms, a new crust formed on nearly all aspects (3/4 melt-freeze crust) following a few mild and sunny days midweek. The crust was thicker on sunny aspects that had gone through several melt-freeze cycles. Below the 3/4 crust, the upper snowpack is generally right-side up with increasing density the deeper you dig.  The 2/23 crust can still be found 12-16" below the 3/4 crust.  Weak snow (facets) were observed below this crust on Thursday but avalanches on this layer seem unlikely. The mid-Jan crust layer that has been so prominent in the Cascades can still be found in the Hurricane Ridge area albeit at much shallower depths; ~4 ft below the surface.  Avalanches down to this layer have not been observed in the Hurricane Ridge area in over a month but it's still worth tracking as we wait to see what March has in store for us.  

The snowpack is quite deep and healthy for this time of year, 130% of normal as of March 1st. 

Make sure to check out the Conditions blog for more info about the very large avalanches that have released throughout the central and southern Cascades over the past two weeks.  There are some impressive photos of a few of these monster slides included in the media reel below.  

2020-21 Forecast Schedule: Avalanche danger ratings will be issued for the Olympics every Friday through Sunday and during mid-week holidays. During the week when the Hurricane Ridge road is closed, forecast information will be updated daily to include expected conditions and relevant travel advice under the No Rating label.

During the ongoing Covid-19 pandemic, continue to follow the latest guidance from local, state, and federal health officials. Avoid unnecessary risks that could impact first responders and stress medical resources.  Wear a mask when appropriate, practice social distancing, and consider recreating closer to home.

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