This is an ARCHIVED report in relation to a cornice collapse fatality on 3/30

Backcountry Avalanche Forecast
West Slopes South
Issued: Friday, March 29, 2024 - 6:32PM
Expires: Saturday, March 30, 2024 - 6:30PM
Author: Andy Harrington

THE BOTTOM LINE

Sunshine and increasingly warm weather will result in an uptick in wet avalanche potential on Saturday. Once the snow surface gets wet and weak, head for shadier slopes where these difficult-to-forecast slides are less likely. Be mindful of terrain above you that could be in the sun and shed snow down towards your location.

Avalanche Danger
Saturday, March 30, 2024
All Elevations: 2 - Moderate

Avalanche Problems (2)

Problem #1: Wet Loose
Aspect/Elevation
W - S - E All elevations
Likelihood: Likely
Size: Small (D1)

We're entering another warm and sunny period, meaning wet avalanches should be at the forefront of your mind. On Saturday, sunshine and daytime warming will be the significant drivers in creating the conditions required for wet avalanche activity. Once the snow surface becomes wet and weak, you'll start to see rollerballs, pinwheels, and eventually wet avalanches. We expect the majority of these slides to be loose avalanches, which often start at a point near rocks or trees. They can grow large and powerful as they descend and gather snow. In some areas, they could even trigger slabs. Your best management tool will be to stick to shaded slopes to avoid these difficult to predict slides.

In isolated locations, larger, more unpredictable shed-style avalanches could occur. Cornice collapses, glides, or even wet slabs could happen over the next few days. Keep an eye on the terrain above you, and don't linger where you see precariously hanging blocks of snow.

Problem #2: Wind Slab
Aspect/Elevation: 5500 - 8000 ft (mid-high elevations) All aspects
Likelihood: Possible
Size: Small (D1) to Large (D2)

At upper elevations, drier snow and the potential for slab avalanches exists. They could be found on any aspect in the morning but may be confined to shaded slopes by day's end. You're more likely to trigger one in wind-loaded terrain. Look for visual clues such as textured surfaces, smooth pillow-like drifts, or new cornices to help identify wind-loaded features. Wind slabs commonly form in confined chutes, on convex rollovers, or near the base of cliffs/rocks. Using small test slopes can give you information about how these slabs may be reacting to your weight. If you suspect a slope is wind-loaded, choose a different route.

Forecast Discussion

We're heading into another springtime warm-up in the West South zone. You might recall that we just dealt with a similar scenario a few weeks ago, resulting in widespread wet avalanche activity. The next few days shouldn't be quite as warm as last time or last as long. 

We've had a week of snow showers with fluctuating freezing levels around the zone. Generally speaking, this has resulted in high-elevation dry snow and lower-elevation moist/wet snow. Of course, there's a transition zone at middle elevations where you'll likely find a mix of avalanche problems and moisture content. Multiple human-triggered and a handful of natural slab avalanches were reported on Wednesday and Thursday near the crest. As the storm snow started to settle and the sun peeked out on Friday, wet avalanche activity increased. Crystal Mountain Pro Patrol reported a human-triggered slab that gathered moist snow as it descended and grew large.

As we march into a warmer and sunnier weekend, expect this pattern to continue. Dry snow problems will continue to diminish while wet avalanche problems intensify. Wet avalanches are notoriously challenging to forecast peak instability, and the problems can be intermingled. We could see the mountains start to fall apart on Saturday, or it may not happen until Monday or Tuesday. So stay vigilant and know that it's likely coming at some point over the next few days. 

Roughly 1-2 feet below the surface, you'll find a crust from the big warm-up a few weeks ago. We anticipate most avalanche activity to occur above this easily identifiable interface during this event. It could make a good sliding surface for wet loose to gather additional snow and increase in size, like the slide at Crystal on Friday.

Low elevations have less snow than average, and this event may put some into permanent summer mode. Expect shallow coverage, open creeks, and punchy wet snow. In areas where adequate snow coverage exists, expect wet avalanche activity.