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Avalanche Forecast

Archived

Mar 2nd, 2020–Mar 3rd, 2020

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

Regions

South Rockies.

The warm to cold temperature trend has helped to stabilize the storm snow, but we still have a lingering deep persistent slab problem in play which makes it impossible to have 100% confidence, especially in bigger alpine terrain features.

Confidence

Moderate - Uncertainty is due to the fact that deep persistent slabs are particularly difficult to forecast.

Weather Forecast

A few weak frontal systems will graze the region this week with sustained mild temperatures.

MONDAY NIGHT: Cloudy, light flurries with trace accumulations of snow, strong west wind, freezing level around 1200 m with alpine temperatures around -5 C.

TUESDAY: Mix of sun and cloud, freezing level climbs from 1200 to 1800 m, moderate to strong west wind, alpine high temperatures around -3 C.

WEDNESDAY: Scattered flurries with 5-10 cm of snow, moderate to strong west wind, freezing level dropping from 1800 to 1300 m, with alpine temperatures dropping to -5 C.

THURSDAY: Mostly sunny, freezing level climbing from valley bottom to 2000 m in the afternoon, moderate southwest wind, alpine temperatures reach 0 C.

Avalanche Summary

No new avalanches were reported on Monday. One of our field team members got out for a flight Friday, and she found a slab avalanche on a steep east/southeast facing alpine feature. Aside from that and a bit of loose wet activity on solar aspects, there has been little reported recent avalanche activity.

The most recent deep persistent slab activity we know about is described in this Mountain Information Network (MIN) report from February 11 and this MIN report on February 9. 

Snowpack Summary

The South Rockies picked up at about 7 cm of snow over the weekend, followed by strong to extreme wind out of the southwest which has formed thin wind slabs in high elevation terrain, especially that immediately lee of ridge crest.

Under this new snow is a crust that may extend as high as 2300 m on solar aspects. It is present on all aspects to 1700 m.  

A thick rain crust sits 40-80 cm below the surface and can be found up to 2100 m. Avalanche activity was last observed at the faceting interface between this crust and overlying snow on February 17. 

The mid-pack is well settled and strong, but the base of the snowpack contains basal facets that are most prominent in shallow rocky start zones.

Terrain and Travel

  • Watch for wind-loaded pockets especially around ridgecrest and in extreme terrain.
  • Conditions may have improved, but be mindful that deep instabilities are still present.
  • Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.