Avalanche forecast

West Slopes North

Northwest Avalanche Center
View on map

Avalanche danger

Wed
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
Open full map
Out of date — this forecast expired 6 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Increasing winds and continued snowfall will maintain dangerous avalanche conditions Tuesday. Natural avalanches are possible and human-triggered avalanches are likely at upper elevations. Pay attention as you transition into wind affected terrain and avoid slopes 35 degrees and steeper.  

Avalanche problems

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2

    Light to moderate snowfall will continue over the next 24 hours adding to the 16-18in of new snow since Friday night. Expect westerly winds to increase throughout the day Tuesday building the thickest and most reactive slabs in leeward upper elevation terrain. Observers over the holiday weekend reported touchy conditions with several natural and triggered avalanches to destructive size 2. Avalanches broke on the old/new snow interface (February 13) and on inter-storm layers. Incremental loading will continue, and fresh slabs will remain reactive to human traffic, especially on slopes 35 degrees and steeper near and above treeline. Give the new snow time to settle and stabilize before venturing into aggressive terrain. Loose-dry sluffs may also run far and fast and could even trigger slab avalanches as they run downslope. Carefully assess how new snow bonds to itself and old snow surfaces and watch for shooting cracks, collapses, and recent avalanches. Seek out supported and lower-angled slopes to reduce your risk. 

    (2/14/2021) A skier-triggered avalanche on a south aspect at 4600ft on Mt. Herman. The avalanche failed 8-12in deep on the old/new snow interface buried February 13 which was a crust on this slope. Photo: Michael Bartley

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    2–3

    The last reported avalanche that failed on the deep persistent weak layer (mid-January crust/facets) occurred on February 3. Observations targeting this layer continue to show gradually improving stability, with signs of the weak layer healing (rounding) and more favorable snowpack test results (resistant and non-planar fractures and no propagation). Regardless, these conditions come with uncertainty and present a low likelihood/high consequence scenario. The layer continues to become more difficult to trigger with time, and deep persistent slab avalanches have become unlikely. Large triggers like cornice fall or motorized users have the best chance to affect such a deeply buried weak layer. Continue to build in a wide margin for error and approach steep open slopes above 4500ft with a cautious mindset. Utilize good travel practices like riding one at a time and keeping eyes on your partners. If you must travel near or below steep upper elevation slopes, your best options are areas where avalanches on this layer already occurred.

    (2/11/2021) Note the mid-January PWL ↓150cm in this location. Weaker snow was found above the 1/13 crust, but it was rounding and gaining strength on this NW aspect at 5000ft in the Twin Sisters area.

Avalanche Discussion

Two skiers triggered an avalanche on a SE aspect at 4600ft near Herman Saddle on Sunday. Both skiers were caught and carried by the avalanche but they remained on the surface of the debris and were uninjured. The avalanche was estimated to be 6-12in deep 200ft wide and ran 50 vertical feet downslope (observation). An observer witnessed a large natural avalanche on the north side of Mt. Herman on Sunday afternoon and captured a photo of the powder cloud (check out the media gallery below). Less precipitation than expected came Monday, but incremental loading over the past 3 days is stacking up, maintaining dangerous avalanche conditions. With strong westerly winds Tuesday afternoon, fresh slabs of wind drifted snow will become increasingly reactive in leeward upper elevation terrain. These conditions require conservative terrain and travel choices. Non-avalanche hazards also exist at this time including tree well and deep snow immersion. Find out more information about deep snow safety HERE.

During the ongoing Covid-19 pandemic, continue to follow the latest guidance from local, state, and federal health officials. Avoid unnecessary risks that could impact first responders and stress medical resources.  Wear a mask when appropriate, practice social distancing, and consider recreating closer to home.

Regions covered