Avalanche forecast

West Slopes South

Northwest Avalanche Center
View on map

Avalanche danger

Mon
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
2 · Moderate
Open full map
Out of date — this forecast expired 4 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Stormy weather will start to push the avalanche danger upwards on Sunday throughout the West South zone. Avalanches should be easier to trigger on steep convex slopes or in wind-loaded terrain. Start to think about avoiding these areas once 6” of snow has fallen or if you see red flag signs of instability during your travels.

Avalanche problems

  • Storm Slabs

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

    Incoming snow and wind will bury a variety of snow surfaces on Sunday as we move into a stormy pattern that will increase avalanche potential over the next few days. Avalanches may act differently based upon the surface they fall on and the terrain’s exposure to wind. In some areas, you may see some surprising avalanches that break widely or connect terrain features, requiring you to dial your terrain choices way back. In areas of the zone where more than 6” of new snow has fallen, use small test slopes to see how the new snow is reacting to your weight or use quick hand pits as you travel to see how it has bonded to the old snow surface. In areas that are prone to collecting wind-drifted snow such as the lee side of ridgelines or rocky chutes and gullies, slabs may be thicker and possibly stiffer. Identifying slab potential, seeing poor bonding in your tests, or noticing red flag signs of instability such as recent avalanches, shooting cracks, or whumpfing collapses should steer you away from steeper slopes over 35 degrees. 

    (2/24/2022) A long (10') shooting crack in a firm pillow-like wind drift. Look for these and other red flag signs of instability as an indicator to head for lower-angled terrain. Photo: Dallas Glass

Avalanche Discussion

The West South’s snowpack is considered to have a generally strong base with differences in the upper snowpack depending on aspect and elevation. In some areas of the zone, there are snow surfaces that we consider weak and capable of producing surprising avalanches on Sunday. We are expecting most avalanche activity to involve the new snow, but can’t rule out isolated events down to the Valentine’s Day Crust. Here’s some more information regarding the intricacies of the upper snowpack:

  • On slopes that typically see direct sunshine, snow should be falling on a melt-freeze crust formed during sunny weather in the latter part of the past week. This crust will vary in thickness based on the amount of sunshine that slope has received recently. Just below it, NWAC forecasters near Crystal Mountain found a thin layer of weak snow (facets) and cold dry snow above the 2/19 interface on Saturday. 
  • On shadier slopes, this sun crust may not exist or could be more subtle. In its place should be settled storm snow from last weekend over the 2/19. Weak surface snow (surface hoar and near-surface facets) has recently been reported on shady slopes and is more likely to persist and produce surprising avalanches on Sunday in these locations. 
  • The higher you ascend in elevation, the previous snow surface should be more wind-affected and possibly more irregular. Wind scoured surfaces, textured snow, or even stubborn Wind Slabs were all reported prior to this storm. Some of these slabs formed in unusual locations due to cold east winds.
  • The Valentine’s Day Crust is an easily identifiable interface that should be around a foot below the surface near the crest, and closer to 1.5 feet on the volcanoes. Where it exists, the more subtle 2/19 crust should be just a few inches above it. In some locations, you may not be able to discern between the two as they have welded together. Both of these interfaces have confirmed weak snow (~1mm facets) associated with them. Our expectation is that Sunday’s snowfall will not be enough to see widespread action on these layers.

As Sunday progresses, temperatures should start to elevate and could start to produce “upside-down” heavy over lighter snow, making avalanches more likely. This same warm-up could bring some rain to lower elevations, initiating small Wet Loose avalanches on steep slopes for you to steer around. As we roll into the evening hours, more significant and warmer precipitation will be on our doorstep. This second round of precipitation should drive more dangerous avalanche conditions and could bring the deeper 2/19 and Valentine’s Day Crusts into play. Be on the lookout for weather changes that could indicate that this more significant wave is arriving earlier than forecast. Sunday evening will not be an ideal time to spend a night out in the mountains.

Regions covered