Bollettino valanghe

Stevens Pass

Northwest Avalanche Center
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In sintesi

Wind slabs are becoming more stubborn, but some potential still exists to trigger one, especially on steep and unsupported slopes at upper elevations. If you get out, make a note of snow surfaces ahead of our next significant winter storm. 

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2.5

    Winds blew from the east once again on Monday. This 'offshore' breeze has been the dominant wind direction since Saturday. Recent, mainly small wind slabs have been observed on open, exposed slopes. These slabs are becoming more stubborn to trigger, but cold temperatures and faceted snow may preserve the instability longer than usual. Identify large, open, and steep slopes where cohesive drifts of snow may exist. Look for surface textures and feel for stiffer snow as you travel to get an idea of steeper areas you may want to steer around. Very steep and unsupported slopes at upper elevations are ones to particularly consider steering around. 

    If you receive any "red flag" signs of instability like whumpfing collapses or recent large avalanches, stick to lower-angle and supported terrain. The 4-6ft of recent storm snow is resting on crusts and weaker snow buried in late December, and a few deeper and larger avalanches occurred around the 11th. While triggering one of these deeper slabs has become unlikely, the potentially problematic structure still exists. A smaller avalanche or large cornice fall could potentially step down to these deeper layers in larger and unsupported terrain features. 

    (1/14/2024)

    A small windslab  likely released on 1/13 with strong easterly winds. 

    Photo: Matt Primomo

Avalanche Discussion

A little sun may poke through the clouds Tuesday morning, but the day should cloud up quickly. Snow surfaces are still very nice cold powder in many sheltered areas. Steep south aspects may hold a thin sun crust after a couple days of direct sun and slightly warming temperatures. The cold temperatures have promoted faceting of snow surfaces on all aspects. On higher, wind-exposed slopes you may find varying degrees of wind-stiffened snow. 

An NWAC forecaster near Arrowhead's summit reported finding some areas with a thin zipper crust and about 10cm of faceted snow above it. On Sunday, we toured near Smithbrook, finding fresh and overhung cornices on northeast aspects. The snow surfaces on south facing slopes were just ever so slightly affected by the sun later in the day. Small facets likely formed above the new thin sun crust, called radiation recrystallization. An interesting 'step down' avalanche was observed on the NE side of Jove Peak (see photo below). This may have been from the heavy snowfall event and strong winds on the 11th. Another larger avalanche was estimated to have run on the 11th off the S side of Rock Mountain in the Camp Chutes. It stopped low in the track. On Saturday, a number of folks in the clear-cut zone of Henry Creek found lots of wind-affected snow surfaces from the active east winds. Above 4,500ft observers reported much less wind, and less wind affected snow, so the easterlies may have been confined to lower elevations in some areas. On open, exposed areas to the wind, you might find stiff wind board-like snow surfaces mixed in with softer areas. 

Between the 6th and 11th the zone picked up around 5 feet of snow, with strong to extreme winds at times. Many avalanches that occurred have become difficult to observe as they're sifted over by wind drifting, or buried by more recent snow. 3 larger avalanches have stood out; The very large step down slide on the NE side of Jove (est 1/11), A large avalanche on the S side of Rock Mountain west of Berne (est 1/11), and an explosive triggered slab 6ft deep in a heavily wind loaded area near Gemini Pass at Stevens Pass Mtn Resort on the 10th. The layer responsible for these larger slides is likely the Solstice crust, which is now about 4 feet below the surface in much of the zone. Snow profiles have shown these weak layers to consist of faceted melt forms, and some snowpack tests have given sudden and propagating results. Although these deeper weak layers appear to be dormant for the time being, they're worth considering in your terrain selection. They could become active again with a large enough load.

Further east there is a similar but shallower snowpack structure. Here, persistent slabs are trending less likely, but remain on the menu. 

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