Use extra caution this weekend. Note the persistent slab problem 70-100cm deep beneath last week’s hard wind slabs. This is a dangerous time to be in avalanche terrain. Remember that most avalanche accidents occur during times of Considerable danger.
Above 2,500ft Considerable
1,500 to 2,500ft Considerable
Below 1,500ft Moderate
Degrees of Avalanche Danger ?
Problem #1: Persistent Slab
Distribution: All aspects, especially wind loaded slopes and cross-loaded terrain features, treeline and up. Cold weather and wind loading over the last 2 weeks has created layered hard slab in the alpine with lots of weak, facetted snow underneath. There’s also an old rain crust 70+cm down which is beginning to facet (see profile below). We’re seeing easy failures and propagation on these layers almost a meter deep, and this danger will persist for a while. These slabs are underneath the new snow, so you’ll need to be thinking about deeper layers and digging to assess them. This is a dangerous time to be in avalanche terrain.
Problem #2: Wind Slab
Distribution: Wind loaded lee slopes (mainly SW-S-SE-E aspects) from treeline and up. NW winds are increasing, blowing the new storm snow into fresh wind slabs at the top of the snowpack. Cold temperatures will limit the amount of bonding between these layers. These fresh slabs have weak snow underneath and will be sensitive to human weight. Avoid wind loaded slopes 25-degrees and steeper.
Problem #3: Deep Slab
Distribution: Isolated, on wind-blown slopes with thin snowpack less than 1m thick. Generally around ridgelines, and anywhere rocks are exposed or thinly buried. All aspects. Elevations above 3000ft. In the Pass zone, there are extensive weak facets at the ground in any areas of thin snowpack. We’re now seeing natural slides on this basal facet layer in areas north of the Pass (see photo). Even in places with deeper snow, there remain trigger points near rocks/thin areas. If you were to trigger a slide on this layer, it would be a deep, wide, hard slab avalanche with deadly consequences. This is a low-probability high-danger situation that is very difficult to manage, so it’s best to exercise caution. Be very careful to avoid rocky trigger points and thin areas. Stick to slopes with a deeper, more uniform snowpack.
Recent Avalanche Activity
The last observed avalanche activity was during the last storm cycle Feb 11-15th. There was a natural avalanche cycle within the new storm snow, with widespread D2-D3 slides on all aspects. These were dry slabs above 4000ft, and some nasty wet slabs below that level. A few large avalanches occurred, with crowns up to 2m tall. Some slides hit the valley floors and lower runouts.
Thursday-Saturday will transition us to offshore flow with some clearing possible (especially Saturday) and north winds increasing. Alpine temperatures are staring around 15-20F and will drop to 5-15F over the next few days. Another shot of snow will hit Sunday-Monday.
Snow totals this week:
3-8″ Wednesday (higher amounts up the highway and less near town)
5-10″ Tuesday (lower amounts toward the border)
8-18″ Monday (lower amounts toward the border)
All of the new snow came in as cold-smoke: low density with snow ratios near 20:1.
Additional Info & Media
This is an important time to practice good group management skills and risk-reduction. This means keeping your group spread out while traveling in avalanche terrain. Ride one-at-a-time in any areas of risk, and only group up in safe zones well out of harms way. Evaluate each slope carefully, have an escape route, and a plan for what to do if an avalanche occurs. Always make sure every rider has a beacon, shovel, and probe, and knows how to use them.