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Avalanche Forecast

Archived

Jan 19th, 2020–Jan 20th, 2020

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

Regions

South Rockies.

It's incredibly difficult to forecast what will happen with dramatic warming and sun. Potentially large cornice failure and loose wet avalanche activity is likely to be widespread, probably best to avoid avalanche terrain Monday as the snowpack feels the heat for the first time.

Confidence

Low - Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather. Uncertainty is due to the timing or intensity of solar radiation and its effect on the snowpack. Uncertainty is due to rapidly fluctuating freezing levels.

Weather Forecast

Warm air invades the region Monday pushing the temperature to near zero from valley bottom all the way up to 3000 m with just a few clouds and strong southwest wind. Tuesday and Wednesday are still warm with the freezing level hanging out around 1500 m.

SUNDAY NIGHT: Freezing level at valley bottom, moderate to strong west/southwest wind, trace of snow possible.

MONDAY: A few clouds at dawn with clear skies in the afternoon, air temperature warming to near 0 C as high as 3000 m, light southwest wind at lower elevations, strong southwest wind at ridgetop, no significant precipitation. Freezing level returning to valley bottom Monday Night.

TUESDAY: Broken cloud cover, freezing level rising from valley bottom to about 1500 m, light southwest wind at lower elevations, strong southwest wind at ridgetop, 1 to 2 cm of snow possible at upper elevations with potential for light rain down low.

WEDNESDAY: Scattered cloud cover at dawn with clear skies in the afternoon, light southwest wind at valley bottom with strong west/northwest wind at ridgetop, trace of precipitation possible.

Avalanche Summary

No new avalanche activity to report from Saturday.

On Friday wind slab avalanches to size 1 were sensitive to control work on a southeast facing ridge crest around 2000 m. Small natural avalanches were also observed on steep rolls.

On Thursday a natural size 2 wind slab stepped down to the deep persistent basal facets below a rock band, details here.  

Snowpack Summary

Recent snow has been loaded into pockets of soft wind slab in alpine lees, and is settling in the mild alpine temperatures. At lower elevations it may remain unconsolidated. 

A well consolidated mid-snowpack overlies a generally weak basal snowpack. The bottom 10-20 cm of the snowpack consists of facets and deteriorating crusts. There is potential for this deep persistent layer to reawaken as temperatures warm on Monday.

Terrain and Travel

  • Minimize overhead exposure; avalanches triggered by warming or cornice fall may be large and destructive.
  • Be aware that wet activity at low elevations is a classic situation for step-down failures in deeply buried persistent weak layers.
  • A moist or wet snow surface, pinwheeling and natural avalanches are all indicators of a weakening snowpack.
  • Avoid exposure to sunny slopes, especially in the afternoon.

Problems

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

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.