Avalanche Forecast
South Columbia
A buried persistent weak layer may roar back to life over the next few days as the freezing level rises and the sun comes out. South facing slopes are especially suspect and are best avoided at this time.
Avalanche Problem 1: Persistent Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- Pay attention to overhead hazards like cornices which could trigger persistent slab avalanches.
- Use caution around sheltered steep or convex slopes where buried surface hoar may be preserved.
- Minimize exposure to steep south-facing slopes where recent storm snow overlies a crust.
Avalanche Problem 2: Storm Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
A few more cm of new snow are expected Saturday night with moderate west/southwest wind which may form fresh shallow slabs immediately lee of ridge crest. If the sun breaks through the clouds Sunday it may initiate natural avalanche activity.
Travel and Terrain Advice
- Be cautious of sluffing in steep terrain.
- Be especially careful with wind loaded pockets near ridge crests and roll-overs.
- Minimize exposure to steep, sun exposed slopes if the strong April sun comes out.
Avalanche Summary
Warming temperatures on Friday initiated loose wet avalanche activity to size 1.5 on a variety of aspects. Small storm and wind slabs were sensitive to skier triggering on steep unsupported features at upper elevations too.
On Thursday warming temperatures initiated large loose wet avalanches to size 3 on south facing aspects between 2100 and 2700 m in the neighboring Glacier National Park. A natural size 2.5 wet slab was observed on a southeast facing feature at 2200 m as well.
Snowpack Summary
Saturday's new snow is coming to rest on a weak surface crust that exists on all aspects aside from true north below 2000 m. This crust extends up to around 2500 m on south facing slopes. On north facing slopes above 2000 m, temperatures have remained cold and the snowpack is still quite "winter-like." Warming temperatures and time have helped to settle the upper 30 to 40 cm just below the surface.
The main concern is the mid-March Persistent Weak Layer (PWL) which is now 60 to 100 cm below the surface. This layer is composed of a crust on all aspects at low elevations. At upper elevations the layer presents as a crust on solar aspects (those that face south and west) and buried surface hoar on polar aspects (those that face north and east). The reactivity of this interface has been steadily decreasing and while the likelihood of triggering a deeper persistent slab avalanche is lowering, the consequence of doing so remains high. Solar aspects are expected to be the most suspect as the freezing level begins to rise over the next few days.
Deeper persistent weak layers from January and December are still being reported by professional observers, but are generally considered dormant.
Weather Forecast
Continued snowfall is expected Saturday night as an unstable air mass fuels convective precipitation. A ridge is expected to build offshore Sunday allowing the entire province to dry out. A more spring-like pattern begins to take shape on Monday with freezing levels creeping towards 2500 m by Tuesday.
SATURDAY NIGHT: Overcast, freezing level around 1000 m, light to moderate west/southwest wind, 5 to 10 cm of snow possible.
SUNDAY: Broken cloud cover, freezing level beginning around 1000 m rising to about 2000 m, light to moderate northwest wind, 1 to 5 cm of snow possible.
MONDAY: Scattered cloud cover, freezing level beginning around 1500 m rising to about 2000 m, light west/southwest wind, no snow expected.
TUESDAY: Scattered cloud cover, freezing level beginning around 1500 m rising to about 2500 m, light to moderate south/southwest wind, no significant precipitation expected.
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Weak crust and surface hoar 60 to 100 cm below the surface have shown prolonged reactivity since the last storm. South facing features have been the most reactive as of late, and this trend is expected to continue as temperatures rise next week.