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Avalanche Forecast

Archived

Feb 29th, 2020–Mar 1st, 2020

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

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 alpine terrain features.

Confidence

Moderate - Uncertainty is due to the limited number of field observations. Uncertainty is due to the fact that deep persistent slabs are particularly difficult to forecast.

Weather Forecast

Warmer funky weather is with us for the forecast period.

SATURDAY NIGHT: Freezing level returning to valley bottom, light variable wind, 1 to 5 cm of snow possible.

SUNDAY: Broken cloud cover in the morning with some afternoon clearing, freezing level beginning at valley bottom rising to 1500 m during the day, light west/southwest wind, no significant precipitation expected.

MONDAY: Clear skies at dawn building to scattered cloud cover in the afternoon, freezing level beginning at valley bottom rising to 1900 m during the day and then staying there until Thursday morning, light west wind at lower elevations, strong northwest wind at mountain top, no precipitation expected.

TUESDAY: Scattered cloud cover, freezing level holding around 1900 m, moderate to strong west/southwest wind, no significant precipitation expected.

Avalanche Summary

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 MIN report from February 11 and this MIN report on February 9. 

Snowpack Summary

The 10 to 35 cm of snow from Sunday/Monday was absolutely hammered by wind Wednesday as evidenced in this MIN submission. Wind was strong enough to get into below treeline features even. Then it got quite warm Friday, the freezing level got to at least 2300 m. The beat up old snow got quite warm and a crust is likely forming on the surface now.  

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

  • Be careful as you transition into wind affected terrain.
  • Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.
  • Conditions may have improved, but be mindful that deep instabilities are still present.

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.