Avalanche Forecast

With the field team back in White Pass we received preliminary observations on Tuesday of a small scale natural wind slab avalanche cycle as a result of recent snowfall meeting with elevated winds, most recently from the west. Slab formation and releases appear to have been limited to alpine terrain thus far. No new persistent slab avalanches have been reported yet.

New surface instabilities aside, a couple of large (size 2-3) persistent slab, human-triggered and natural avalanches were reported last week. These avalanches occurred near ridgetops in north-to-northeast alpine terrain. These avalanches have showed an impressive capability to propagate across large distances. Here is a link to the most recent human-triggered size 3 avalanche.

Looking forward, this persistent problem is expected to grow less likely to trigger but will produce large, destructive avalanches if it is triggered. This means it still needs to factor into terrain decisions.

If you are out in the backcountry please share your observations to the Mountain Information Network!

Wind has impacted 30-40 cm recent snow, this covers a crust up to 1700 m and wind-pressed surfaces at higher elevations.

The bottom portion of the new snow saw some wind effect before being buried, especially from the west but mainly in the alpine. This means slabs at upper elevations may be obscured by more recent low density snow.

A persistent weak layer of surface hoar and/or facets our field team has been tracking is now about 100 cm deep and exists on north facing alpine features. This layer doesn't appear to have produced any recent avalanches in the region and has shifted toward more stubborn results or non-results in snowpack tests this week.

Thursday night

Overnight flurries, 7-12 cm by late Friday morning. Increasing south-southwest winds gusting to 50 km/hr. Treeline low temperature -12 C.

Friday

Isolated morning flurries and sunny breaks later in the day. Gusty southwest wind calming to 20-30 km/hr during the day and increasing in the afternoon. Treeline high temperature -9 C.

Incoming flurries and snow, 5-10 cm through the day. Strong southwest winds. Treeline high temperature -5 C.

Decreasing wind and isolated flurries, 5 cm through the day. Southwest winds easing to moderate. Treeline high temperature -5 C.

More details can be found in the Mountain Weather Forecast.

• Pay attention to the wind, once it starts to blow fresh sensitive wind slabs are likely to form.
• Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
• Persistent slabs have potential to pull back to lower angle terrain.