Bollettino valanghe

West Slopes Central

Northwest Avalanche Center
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Pericolo valanghe

Tue
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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In sintesi

You are most likely to trigger an avalanche on steep slopes holding recently wind drifted snow. Look out for wet avalanches on slopes warming from direct sun exposure. Deeper new snow will be found in areas that see convergence zone snowfall overnight Sunday. Use additional caution if you find more than 8” of new snow.

Problemi valanghivi

  • Wind Slabs

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

    Sunday's storm didn't deliver precipitation to West Central until the end of the day. But snowfall is forecast to continue overnight and be accompanied by wind strong enough to blow it around and drift onto downwind slopes.  Fresh slab formation should be the result. A convergence zone should set up between Hwy 2 and I-90 and deliver additional snowfall to this area.

    Steep, unsupported, wind loaded slopes are where you are most likely to trigger a wind slab. Use the pattern of drifting and scouring, cornices, and other clues to figure out which slopes are holding thicker or more sensitive slabs. Test slopes, wind lips, and other loaded features can provide information about the reactivity of fresh slabs.

    (1/10/2024)

    Wind drifted snow like this can be very soft but it still a sign to look for more loading on leeward slopes.

    Photo: Phil Straub - Cascade Mountain Ascents

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–1.5

    A bit of clearing at dawn could carry into the morning and allow the sun to warm fresh snow. This round of loose snow avalanches is most likely to occur below cliffs and other steep terrain that sheds snow with warming. Most should be small, but big alpine features can still produce some long-running avalanches if the sun stays out for long enough.  A convergence zone should set up between Hwy 2 and I-90 overnight and bring and additional shot of snow to that area.

    Keep an eye on steep slopes picking up sun. Avoid traveling directly below areas where you see the first signs of wet avalanche instability like rollerballs, pinwheels, or very small avalanches. Full cloud cover will return as the next storm moves into the region.  If it's cloudy all day, then wet avalanches would be unlikely.

    (12/9/2024)

    Fresh rollerballs on sunny slopes are an early sign of wet avalanche instability.

    Photo: Toby Swimmer

Avalanche Discussion

Instead of windy and wet weather, much of the forecast zone saw mild temperatures and even some sun. By the end of the day, weather stations around West Central had picked up anywhere from 0.75" (Finney Creek south of Hwy 20) to 0.1" at Skookum Creek near Snoqualmie Pass. Winds likely stayed strong, with the White Chuck Tripod reporting westerly wind for the entire day.  No observations were submitted from West Central.

Observers in Stevens and Snoqualmie Pass reported sunnier-than-expected conditions that allowed for crusts to soften on southerly aspects. While the warming did make for some good riding conditions, it didn't contribute much to avalanche danger.  No new wet avalanches were reported. A number of wet avalanches were reported from shady slopes at Snoqualmie Pass on Satuday.

An NWAC Forecaster in West North and other observers in the area reported no new avalanches as of mid-afternoon. Natural and human-triggered slab avalanches that occurred on Saturday were observed in wind loaded and also wind sheltered terrain. The storm did manage to bring meaningful precipitation Sunday afternoon, with some weather stations picking up 0.2"/hour.

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