Bollettino valanghe

West Slopes South

Northwest Avalanche Center
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Pericolo valanghe

Wed
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
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

A round of strong southeast winds, cloudy skies, and a bit of new snow will make for a rugged day. Avoid steep slopes where you witness active wind loading or that hold smooth, fresh-looking drifts to reduce the odds of triggering an avalanche. If you start seeing natural avalanche activity take a bigger step off and away from wind loaded slopes.

Problemi valanghivi

  • Wind Slabs

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

    Wind slab formation Tuesday will be dependent on a few things. One is the amount of snow available for transport. The slopes providing most of the snow have some amount of crust that holds loose snow in place. Snowfall totals from the last storm also vary widely. On the other hand, a few or more inches of fresh snow farther south in the zone could provide more snow for transport. All of these factors affect how much snow can get drifted onto leeward slopes.

    Southeasterly winds also vary across West South. Expect them to hammer the crest while other areas might see a bit less wind.

    Finally, surface hoar and faceted snow were observed at the surface in other westside zones. Though fresh wind slabs might be fewer in number and size, what you do find might be more reactive than normal if they form over weak snow.

    Blowing snow will be the main observation to identify areas of active wind loading. Test slopes and hand shears will help gauge slab reactivity and depth. You may see slabs form farther downslope or on different aspects than usual.

    Wind? Check. Is snow available for transport? Check. Blowing snow? Yup. Probably some wind slab somewhere on that leeward slope.

    Photo: Katrina Roloff

Avalanche Discussion

An observer just east of White Pass reported moderate winds but a lack notable wind transport Monday. Cold dry snow was found on northerly aspects. No other observations were submitted from West South on Monday.

The most notable observation from the weekend was a large human triggered avalanche in the Tatoosh Range. The crown appears to be 1’-1.5’ deep with wide propagation. Without detailed information about the weak layer and bed surface it’s hard to discern the exact setup that produced this avalanche. It could be an isolated area where a thin layer of faceted snow survived and was buried during the latest storm. Warming conditions and low clouds may also have played some role in increasing reactivity. No other avalanches of this size and type were reported over the weekend.

West South picked up  7”-24” of new snow since the end of last week and temperatures were below normal for this time of year. That helped the new snow stay cold in most but not all locations. The new snow sits on a melt-freeze crust on most aspects (the 3/22 interface). Storm totals increase the further south you travel, especially on the volcanoes. 

Observers found varying conditions across the zone Sunday. On Mount St. Helens there was 2’ of new snow capped by shallow wind slab. The most notable snowpack observation was a layer of graupel above the 3/22 melt-freeze crust. An NWAC Forecaster at Crystal Mountain found 7" of new snow. This highlights the disparity in storm totals across West South. Test results yielded failures on the older 3/14 crust, including propagation during an extended column test. Over at Paradise,  observers reported cold dry snow on shaded slopes, along with plenty of wind effect near ridgelines. Moist surfaces and rollerballs were reported by multiple groups on Saturday afternoon.

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