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Avalanche Forecast

Archived

Mar 15th, 2020–Mar 16th, 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 Coast Inland.

A rapid rise in freezing level is forecast and there is uncertainty on how quickly it will warm the snowpack. It could trigger an avalanche cycle. Treat the hazard as HIGH and avoid avalanche terrain and overhead exposure if you observe natural avalanche activity.

Confidence

High - Confidence is due to a stable weather pattern; little change is expected for several days.

Weather Forecast

SUNDAY NIGHT: Clear skies, light northeast wind, alpine temperature -6 C.

MONDAY: Clear skies, light northeaast wind, alpine temperature 0 C, freezing level 2100 m.

TUESDAY: Mix of sun and cloud, light to moderate northeast wind, alpine temperature -4 C and strong valley-bottom diurnal temperature changes, freezing level 1500 m.

WEDNESDAY: Clear skies, light northwest wind, alpine temperature -4 C and strong valley-bottom diurnal temperature changes, freezing level 1600 m.

Avalanche Summary

Small (size 1) wind slab avalanches were triggered by riders on Saturday in alpine terrain.

Looking forward, loose wet avalanche activity and cornice falls could be triggered with the warming trend. The potential of triggering wind slab avalanches remains possible in steep, alpine terrain.

Snowpack Summary

A rapid warming trend will raise the freezing level to around 2100 m on Monday.The warm air, coupled with strong radiation from the sun with clear skies, may rapidly weaken the snowpack and cornices. Expect to find moist or wet snow during the day, particularly on sun-exposed slopes, which could freeze into a melt-freeze crust overnight.

In the alpine, hard wind slabs may be found on all aspects due to variable wind directions. Recent wind has blown from the northeast, forming wind slabs in south to southwest terrain features. In sheltered terrain, about 30 cm of snow may overly a melt-freeze crust and potentially small surface hoar crystals.

In the northern part of the region (i.e., Duffey/Hurley/Gold Bridge), a deep instability may linger at the base of the snowpack. It has not produced an avalanche since February 17th. If one were to trigger the layer, it would likely be in a thin, shallow, rocky spot. A cornice fall could also trigger it. The likelihood of triggering this layer may increase during this warming trend. 

Terrain and Travel

  • Extra caution for areas experiencing rapidly warming temperatures for the first time.
  • Back off slopes as the surface becomes moist or wet with rising temperatures.
  • Minimize overhead exposure; avalanches triggered by warming or cornice fall may be large and destructive.
  • Carefully evaluate steep lines for wind slabs.
  • The likelihood of deep persistent slab avalanches will increase with each day of warm weather.

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.

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.