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Avalanche Forecast

Archived

Feb 23rd, 2017–Feb 24th, 2017

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Purcells.

Choose supported terrain and watch for shallow snowpack areas where triggering a large persistent slab avalanche remains possible.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

We're into a stable and benign weather pattern with cooling temperatures and isolated flurries.FRIDAY: Cloudy with sunny periods, light winds, alpine temperatures around -14 C.SATURDAY: Flurries starting in the afternoon with accumulations of 2-4 cm, light west winds, alpine temperatures around -14 C.SUNDAY: Flurries with trace amounts in the north and up to 10 cm in the south, light southeast winds, alpine temperatures around -12 C.

Avalanche Summary

On Thursday, a few small loose dry avalanches were reported in steep terrain., On Wednesday, as few size 1 skier triggered slabs were reported in unsupported alpine terrain and a few older size 1-2 storm slabs were reported on northerly aspects. Earlier in the week, there were several large skier triggered avalanches, including a remotely triggered size 2 wind slab near Kimberly, a skier-triggered size 2.5 persistent slab near Golden, and a remotely-triggered size 3 persistent slab near Golden. See here for a MIN report from one of the large avalanches near Golden.Small avalanches in the new storm snow remain the primary concern on Friday, but remember they have the potential to step down and trigger persistent slab avalanches.

Snowpack Summary

Light flurries over the past few days have delivered 10-25 cm of low density snow. Expect to find isolated pockets with thicker wind deposits at higher elevations as well as sun crusts forming on steep south-facing slopes. The recent snow has buried the mid-February interface, which is composed of a thick rain crust up to about 2000 m, sun crusts on steep solar aspects, and spotty surface hoar on shaded aspects. Storm snow from previous weeks is still bonding poorly to the February 3rd surface hoar / sun crust layer, which is now down 60-80 cm. A persistent weakness buried mid January is about a metre deep and the November crust is about 1.5 metres deep. These deep persistent weaknesses still have the potential to wake up and become reactive with human triggers. (See MIN post above).

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.