Expect pockets of wind slabs to remain reactive to riders in exposed areas near ridge tops. If triggered, these slabs may step down to deeper layers, resulting in surprisingly large avalanches.
Wind slab avalanches are possible at upper elevations where wind has blown dry snow into unstable slabs. While these slabs may be thin, they could be poorly bonded to the underlying snow, so be extra cautious in lee terrain and convex rolls.
A persistent slab problem formed by a crust down 90-160 cm has created a low likelihood, high consequence scenario that is difficult to forecast. It is uncertain how the forecast warm temperatures have affected the snowpack and if we will see more activity on this layer after the warm period. Avoid likely trigger spots such as steep, rocky slopes with a shallow or thin-to-thick snowpack.
FRIDAY NIGHT: Cloudy, no precipitation, light southwest wind, treeline and alpine temperatures around -7 C, possible temperature inversion with alpine temperatures of -3 C, freezing level around 1000 m.
SATURDAY: Cloudy with flurries, moderate to strong southwest wind, treeline temperatures around -5 C, freezing level around 1200 m.
SUNDAY: Cloudy, no precipitation, moderate westerly wind, treeline temperatures around -6 C, possible temperature inversion with alpine temperatures of -3 C, freezing level around 500 m rising to 1000 m by midday.
MONDAY: Flurries up to 5 cm, moderate to strong westerly wind, treeline temperatures around -5 C, freezing level around 1200 m.
A natural cycle occurred Thursday releasing several large natural avalanches (size 2.5): storm slabs in alpine terrain, cornice falls pulling storm slabs, wind slabs and wet slabs running to valley bottom. Smaller loose avalanches were also triggered by solar input and warm temperatures at lower elevations.
Wednesday's storm resulted in some small (mostly size 1) slab avalanches in the top 15 cm of new snow. Explosive control in the Invermere area keep producing few size 2 avalanches that failed on the early December persistent weak layer. These occurred on relatively shallow northeast-facing slopes at 2000 m, where the layer was buried 60-80 cm deep.
We have seen sporadic avalanche activity on this persistent weak layer since Jan 4. These have included some large human triggered avalanches, such as this size 3.5 avalanche just outside the region at Pedley Pass on Jan 4 and this avalanche near Golden on Jan 9, as well as large natural avalanches like this one reported in the South Purcells on Jan 9. These avalanches suggest the persistent slab problem is an ongoing concern in the Purcells.
A breakable crust is now capping the recent 15-20 cm of snow which is continuing to settle. This crust seems thinner on north and east slopes but present up to 2000 m. Surfaces at lower elevations have gone through a melt-freeze cycle. Dry snow can still be found in alpine terrain, although it will likely be wind-affected. This most recent snow has buried some small surface hoar and melt-freeze crusts. The snow is likely to have bonded to these layers relatively quickly, but could remain unstable in isolated pockets. The most notable layer of concern in the snowpack is a crust that was formed in early December and is now down 90-160 cm. Activity on this layer has been sporadic but has generally been triggered on steep, rocky slopes, with a shallow or thin-to-thick snowpack.
