Avalanche Forecast
Purcells
Expect new snow and strong winds to form storm slabs and grow fragile cornices. Cracking around skis and sleds are signs that the new snow is bonding poorly to the old surface. Avoid wind loaded areas with pillowy or chalky looking snow.
Avalanche Problem 1: Storm Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- Be careful with with loaded pockets, especially near ridge crests and roll-overs.
- Watch for whumpfing, hollow sounds, and shooting cracks.
- If triggered the wind slabs may step down to deeper layers resulting in large avalanches.
Avalanche Problem 2: Persistent Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Buried weak layers exist in the snowpack and may be reactive to large triggers such as a cornice or step down from a wind slab release. Human triggering may also be possible in shallow or thin, rocky, unsupported terrain.
Travel and Terrain Advice
- Pay attention to overhead hazards like cornices which could easily trigger persistent slabs.
- Avoid steep convexities or areas with a thin or variable snowpack.
Avalanche Summary
Explosive control work on Friday produced and cornice and wind slab results (size 1.5-2) all of which failed in the upper snowpack.
Thursday there were reports of large (size 2.5 and 3) natural cornice triggered avalanches on northerly aspects above 2400 m, one initiated a slab failure at the base of the snowpack, 250 cm deep.
On Wednesday there were reports of several skier triggered slab avalanches up to size 2 on predominantly steep, south-facing features failing on the crust/surface hoar interface buried mid-February.
Tuesday there were reports of a skier triggered size 2.5 cornice failure that produced very large, bus-sized cornice chunks on an north aspect at 2400m.
And Monday, we received reports of a cornice triggered size 2.5 slab avalanche on a high north east alpine face near 2900 m, as well as natural wind slabs to size 2.5 on a wide range of aspects above 1900 m elevation.
Although deeper, persistent avalanche activity has become less frequent over the past week, light triggers in shallow rocky areas, as well as large triggers such as a cornice collapse or step down from a wind slab release, still have the potential to result in large destructive avalanches.
Snowpack Summary
A light dusting of new snow on Friday now covers storm snow totals from last week that range from15-30 cm, with closer to 50 cm in the very south of the region near Kimberley. Winds have redistributed these accumulations into deeper, reactive slabs in wind-exposed terrain.
These accumulations sit on an interface that was buried mid-February consisting of; a mix of older wind slabs in exposed higher elevation terrain, a sun crust on steep solar aspects, and surface hoar on sheltered slopes. Several recent avalanches have failed on this layer in the past week.
Within the mid and lower snowpack are several persistent weak layers that are beginning to show signs of improving but still remain suspect.
Two surface hoar/ crust layers buried in January are now 80-120 cm below the snow surface. At least one of these layers can be found on all aspects and elevations.
Deeper in the snowpack ( about 150 cm deep) is a facet/crust/surface hoar layer buried in December that is most prevalent at treeline elevations and below.
Near the base of the snowpack is a crust/facet combo layer buried in late November.
Weather Forecast
Snow is expected to begin overnight on Saturday then easing Sunday morning.
SUNDAY: Flurries. Accumulation 5-15 cm. Ridge wind strong to extreme, west. Temperature -8. Freezing level valley bottom.
MONDAY: Mix of sun and cloudy, light flurries. Accumulation trace. Ridge wind light to moderate, west. Temperature -6. Freezing level 600 m.
TUESDAY: Cloudy, flurries. Accumulation 2-5 cm. Ridge wind moderate, southwest. Temperature -6. Freezing level 900 m.
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New snow and strong winds will create storm slabs in many areas in the alpine, as well as open areas at lower elevations. These slabs may be especially deep and touchy in wind-loaded areas on the leeward (down-wind) side of ridges and convex rolls.