Bollettino valanghe

West Slopes North

Northwest Avalanche Center
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Pericolo valanghe

Fri
Alta quota
3 · Marcato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 4 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

A very cold, blustery day is in store for Thursday. Strong easterly winds will build fresh wind slabs above treeline and also in some near treeline areas. Avoid steep slopes where you witness active wind loading to reduce the chance of triggering an avalanche.

Problemi valanghivi

  • Wind Slabs

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

    Gusty winds and plenty of light-density snow equals fresh wind slabs. East winds often come with an unusual pattern. Some mountains and ridges will see sustained strong winds - with lots of wind transport and slab formation - while other areas might remain calm. There will likely be stronger winds farther north and east in the zone but be ready to see them anywhere. 

    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.

    In sheltered terrain older slabs are becoming difficult to trigger but you might still find one on a steep unsupported feature like a convex rollover. 

    Example of the wind scouring snow from windward terrain and transporting it onto leeward slopes below.

  • Loose Dry

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

    There is no shortage of light, fresh snow out there. Dry loose avalanches will mostly be small and present little danger. It could be a different case with terrain traps in the runout or on big steep slopes where they can run far and entrain more snow.

    Clearing skies and sun offset by very cold temperatures won’t be enough to trigger wet loose avalanches. A bit of warming could cause trees and rocks to shed snow which could in turn trigger dry loose snow avalanches.

    These kinds of avalanches shouldn’t take you by surprise - keep an eye on slopes overhead as the sun comes out and stay alert to the amount of snow moving with you if descending steep slopes.

    (2/21/2023)

    Natural dry loose avalanches in Swift Creek.

Avalanche Discussion

AVALANCHE FATALITY: COLCHUCK PK, EAST CENTRAL ZONE: READ THE PRELIMINARY REPORT HERE.

Forecast Discussion:

Observers reported many human triggered dry loose avalanches to D1.5 and also a few D1 wind slab avalanches Wednesday. Winds around the Baker Backcountry were calm and no fresh wind transport was noted. There were no observations from other subzones in West North.

The latest storm produced a less common snowfall pattern due to westerly flow during the bulk of the precipitation. Weather stations on the flanks of Mt. Baker picked up 4-6” of precipitation from Feb 19-21 with 4-6’ or more of new snow near and above treeline. Heather Meadows and the surrounding area - usually the big winner when it comes to precipitation and snowfall - received a bit less with 2.8” of precipitation and about 2-3’ of new snow at treeline.

Avalanche activity varied as well. Widespread natural avalanches were reported from Schriebers/Mt. Baker NRA on Monday. Early Tuesday morning a large natural avalanche ran over 3000’ from high on the south side of the ridge connecting Church Mt. and Excelsior Pass down to below treeline (1900') and put a 10’ deep debris pile on Church Mt. Road. Natural slab and loose snow avalanches were observed Tuesday around the Baker Backcountry but the size and extent of avalanche activity appeared a step lower in number and size.

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