Avalanche Forecast
Issued: Feb 9th, 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.
dsaly,
Avalanche Canada
Winds have pressed snow around ridges and leeward features, the best riding will be in snow unaffected by the wind.
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
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.
Weather Summary
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.
SaturdayIncoming flurries and snow, 5-10 cm through the day. Strong southwest winds. Treeline high temperature -5 C.
SundayDecreasing 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.
Terrain and Travel Advice
- 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.
Problems
Wind Slabs
Steady southwest winds have pressed loose snow, with less wind affect reported on the west side of White Pass compared to the east. Overnight flurries are forecast to deposit 5-15 cm by Friday (the largest amounts for the snowiest spots near White Pass). Reactive pockets may luck where wind deposits snow.
Aspects: North, North East, East, South East, 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 10th, 2023 4:00PM
