Bollettino valanghe

West Slopes South

Northwest Avalanche Center
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Pericolo valanghe

Sat
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 3 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

The snowpack won’t have much time to adjust to the recent load. Strong east winds will kick back up and help maintain dangerous avalanche conditions on Friday. You could see some unique avalanches in unusual locations, so keep it simple by avoiding all slopes over 35 degrees.

Problemi valanghivi

  • Wind Slabs

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

    Easterly winds should ramp back up on Friday. This could thicken existing slabs or build new ones on leeward slopes. Due to the easterly wind direction, these slabs may develop on different aspects than you’re used to. They could also form further down in the terrain as slopes get cross-loaded. Look for actively blowing snow, new cornices, textured surfaces, or fresh drifts to help identify wind-loaded slopes to avoid. Thicker slabs could exist in rocky chutes, near the base of cliffs, or on convex rollovers. Using small test slopes or uptrack tests as you travel can help you determine how sensitive slabs are to human triggers.

    (2/14/2024)

    Signs of wind loading, particularly during an east wind event. Use these visual clues to help identify wind-loaded aspects.

    Photo: Andy Harrington

  • Storm Slabs

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

    In wind-sheltered terrain, plenty of storm snow exists. A gradual warm-up is expected on Friday and could help the low-density snow "slab up" during the day in a few locations. Use small test slopes, uptrack tests, or quick hand pits as you travel to look for heavy snow over weak snow, points of failure, or a poor bond to the old surface. If snow fails in blocks, you’re dealing with a storm slab issue and should avoid convex features over 35 degrees. In isolated locations, slabs could fail on weak snow grains, resulting in surprising avalanches that span far distances or connect terrain features.

    If the snow is light and fluffy but not well bonded, you may have to deal with loose avalanches running on an underlying crust. Don’t get tripped up by one of these in consequential terrain.

    (12/8/2023)

    Hand pits are a great way to look at the recent storm snow. Look for strong over weak layers or points where it fails easily in blocks. 

    Photo: Andy Harrington

Avalanche Discussion

On Thursday, backcountry travelers were greeted by over a foot of low-density snow throughout the zone. On the volcanoes, accumulations ranged up to 1.5 feet of new. Weather stations at White Pass and Crystal recorded easterly winds gusting into the 40s and 50s. 

Avalanche professionals and the White Pass Pro Patrol reported discontinuous wind-loading with some areas scoured down to a crust. In sheltered locations, loose low-density snow sat on a variety of surfaces. At Crystal Mountain, Pro Patrol reported similar effects from the wind - areas scoured down to a crust and slabs as much as 2 feet thick during their morning mitigation work. Cross-loading was observed on northerly terrain, and a few slabs broke widely and wrapped terrain features. 

Snow depth over the Early February Crust (EFC) will now vary significantly around the zone based on your location, aspect, and exposure to wind. Generally speaking, slopes that see direct sunshine will contain less snow and more crusts, sometimes interspersed with weak grains. Depths will be greater near the volcanoes than the crest, and wind-exposed areas could be stripped down to the 2/14, 2/11, or even the EFC. NWAC forecasters found weak grains sitting on the EFC earlier this week in multiple locations within the zone, sometimes sandwiched between a second crust. Focus your observations down to this interface on Friday. 

Weak surface hoar was widespread ahead of this storm. In wind-sheltered terrain, avalanches could break in surprising ways because of it. There’s a chance the sun could come out in the northern half of the zone. If it does and can overcome the cold east wind, expect to see loose avalanche activity. Most should be solar-induced dry loose, but a few could be moist/wet in the right conditions. 

Regioni coperte