Avalanche forecast

West Slopes South

Northwest Avalanche Center
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Avalanche danger

Fri
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Highlights

On Thursday, focus on the recently fallen snow and how firm the underlying crust is. This can help you determine the potential size and reactivity of potential avalanches. Any triggered slide, whether wet or dry could run far distances on the underlying crust.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–1.5

    If you’re going to trigger a slab avalanche on Thursday, it will likely be in wind-loaded terrain at upper elevations. Look for textured surfaces or areas that look “fat” compared to the surrounding landscape to identify wind-loaded features. Using test slopes and hand pits as you travel can give you an indication of the snow’s slab potential and how well it is bonded to the old snow surface. Pay close attention near ridgelines, unsupported slopes, or rocky terrain where you’re more likely to trigger one of these small avalanches.

    (4/12/2023)

    Cracking and some small blocks failing on a wind-loaded feature near a ridgeline on 4/11.

    Photo: Andy Harrington

  • Loose Wet

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

    Periods of sunshine or daytime warming could result in Loose Wet avalanches occurring on steep slopes. If the surface is wet and sticky and you notice snow shedding from trees and rocks or new rollerballs, then wet avalanches may soon follow. Although they may start small, they have the ability to entrain snow and grow large as they descend, sometimes triggering slabs in the process. Your best management tool will be to head for lower-angled slopes keeping aware of overhead hazards.

    (4/8/2023)

    Rollerballs and a small Wet Loose avalanche from a sunny period prior to this storm. Note how these originated near rocky terrain.

    Photo: Andy Harrington

Avalanche Discussion

On Wednesday, NWAC forecasters in the Crystal Mountain backcountry found roughly 5-6 inches of new snow overlaying the 4/11 interface at upper elevations, with considerably less down low. In the morning hours, the storm snow lacked much cohesion except near ridgelines where subtle wind effect was observed. The exception would be on aspects that often see direct sunshine where a breakable surface crust was found in some locations. Crystal Mountain Pro Patrol reported that as the day progressed, daytime warming helped the snow to gain some cohesion and a few small wet avalanches occurred.

Conditions should be similar throughout the zone, except with varying degrees of new snow depth over the 4/11 interface. It goes without saying that wherever you find deeper accumulations, you can expect avalanches to be larger and possibly easier to trigger. We suspect the majority of activity to occur above the 4/11 crust, but in isolated locations, deeper slides could happen given the right trigger. 

Multiple large avalanches were reported earlier this week due to the atmospheric river event that dropped anywhere from 2-3 inches of precipitation (SWE) on our cold mountain snowpack. Most notable were very large (D2.5-3) Wet Slab avalanches triggered by Crystal Patrol with explosives and 5 large to very large slides picked up by seismic equipment used by the USGS on Mount St. Helens.

Barring some unforeseen scenario, this is my last forecast for the season. I wanted to take a minute to thank everyone who submitted observations and helped us out. Have a safe and fun spring touring season. See you in the fall!

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