Avalanche Forecast
Issued: Feb 8th, 2023 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Persistent Slabs.
cgarritty,
Avalanche Canada
Fingers crossed Thursday's wind isn't enough to transform the great powder riding in White Pass into a minefield of wind slabs. Keep those savvy, sheltered terrain options at the ready in case blowing snow tells you the inevitable has arrived early.
Summary
Confidence
Moderate
Avalanche Summary
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!
Snowpack Summary
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.
Weather Summary
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.
Terrain and Travel Advice
- 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.
Problems
Wind Slabs
Until the wind gets to it, 10-15 cm of new low density snow has buried wind slabs formed early this week, predominantly in the alpine. Once the wind does get at it, we'll have a mix of touchy new wind slabs and more stubborn older ones to navigate around.
Avoid steep rocky slopes near ridge crests where a wind slab release might be capable of stepping down to a deeper snowpack layer.
Aspects: North, North East, East, South East, West, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
Buried weak layers produced large, surprising avalanches last week. These layers are on a strengthening trend, but they may still be triggerable where the snowpack is thin.
Avalanche activity associated with this problem was observed on north to northeast alpine terrain on preserved surface hoar that is now buried about 100 cm deep. Keep in mind that large avalanches can run far into flatter terrain and that stiff slabs can also pull back into flatter terrain above them.
Aspects: North, North East, East, South East, West, North West.
Elevations: Alpine.
Likelihood
Expected Size
Valid until: Feb 9th, 2023 4:00PM
