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!

Light flurries with little wind Thursday should bring us to about 30-40 cm of recent snow resting on a variety of wind-affected surfaces and crusts, small surface hoar in places in the alpine, and a widespread 5-10 cm melt-freeze crust below roughly 1700 m.

The bottom portion of our 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.

Wednesday night

Some clearing before clouding over again in the morning. Light southwest winds shifting east and increasing.

Thursday

Increasing cloud and flurries bringing up to 5 cm of new snow over the day, increasing a bit overnight. Light east winds. Treeline high temperatures around -10.

Friday

Becoming mainly sunny before clouding over again in the afternoon. 5-10 cm of new snow from the overnight period. Winds ramping up to strong southwest. Treeline high temperatures around -9.

Saturday

Cloudy with scattered flurries continuing from overnight with less than 10 cm total of new snow by end of day. Strong southwest winds. Treeline high temperatures around -5.

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.
• Wind slabs are most reactive during their formation.
• 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.