Avalanche forecast

West Slopes North

Northwest Avalanche Center
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Avalanche danger

Fri
Alpine
4 · High
Treeline
4 · High
Below
3 · Considerable
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Highlights

A warm, wet, and windy storm should create very dangerous conditions by day’s end. The backcountry terrain around the Mt. Baker Ski Area and Schriebers/south side of Mt. Baker could see widespread natural avalanche activity and HIGH danger by late afternoon. Avoid all avalanche terrain when you observe heavy rain or snowfall, or start seeing wet snow or slab avalanches.

Update @ 7:00:  NTL + ATL danger ratings raised to High for the likelihood and extent of a natural avalanche cycle at the end of the day. 

Avalanche problems

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1.5–2.5

    The combination of heavy snowfall and rising freezing levels is a predictable setup to see slab avalanches. Think upside-down snow - like where your floatation of choice gets trapped in a layer of lighter snow under a thick slab above. These avalanches are more likely in wind loaded terrain or on northerly aspects where a dry, weak snow surface survived recent warming. They can still release on all aspects.

    Thursday won’t be the kind of day to assess stability and pick your way through larger terrain, especially in deteriorating weather conditions. Avoid travel on or under big slopes as snowfall and wind speeds increase through the day and into the evening.  At some point in the afternoon or evening, all avalanche terrain will be a no-go.

     

     

    Heavy precipitation and warming temperatures = storm slabs. Expect to see avalanches like this by Friday morning. Warming temperatures and rain will further weaken large cornices as well.

     

  • Loose Wet

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

    The current snow surface varies greatly by aspect and elevation. Wet or moist snow, crust, and even dry powder can be found, sometimes in close proximity. But below the surface, the snowpack is dry and winter-like. There is plenty of precipitation in the forecast through Friday morning - with snow levels pushing 5000' - to make the current snowpack fall apart. It's more a question of when it will happen than if it will happen.

    Look for initial signs of a wet avalanche instability like rollerballs or snow shedding off trees and rocks. Wet loose avalanches won't be far behind. If you observe heavy rainfall then just avoid being on or under any and all steep slopes. That includes innocuous-looking gullies that funnel avalanches debris from slopes above.

    Wet loose avalanche at the toe of the East Gully of Herman. 

Avalanche Discussion

The most important thing to remember for Thursday is the need to monitor conditions wherever you end up going in the mountains, especially in the afternoon. Expect higher avalanche danger - and move away from avalanche terrain -  if heavy precipitation picks up earlier than forecast or if snow levels rise ahead of schedule.  

Cool, sometimes-sunny, spring-like conditions are taking a leave of absence. The approaching weather system is warm, wet, and windy. This a big change from the dry snow and sunny interludes we have enjoyed in the last week. It's also a strange storm in that precipitation amounts vary widely across the west slopes and even across a single forecast zone like West North. In addition to variability in precipitation, uncertainty as to the exact timing of the heaviest rain and snowfall, and also rising snow levels add another layer of complexity to the avalanche forecast.

Observers across West North found fairly benign conditions Wednesday. Fresh wet loose avalanche activity was less widespread but there is still plenty of avalanche debris at the base of steep slopes that picked up some sun over the past four days.  Easy to trigger, dry loose avalanches found on North Sister are a great indication of weak snow hanging on at the surface on shaded aspects. 

Below the surface is a dry, layered snowpack. The layer interfaces from March 23rd and 31st are easy to identify. Though these interfaces have produced only a handful of slab avalanches since the latest storm, there is a high likelihood we will see some activity on them with the next one.

Regions covered