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Avalanche Forecast

Archived

Mar 4th, 2022–Mar 5th, 2022

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

Sea To Sky.

A weak layer of facets sitting on a firm crust is creating a persistent slab problem which has resulted in numerous human-triggered avalanches over the past few days. Check out the new forecaster blog for more details. 

Confidence

Moderate - Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack. Uncertainty is due to the timing or intensity of solar radiation and its effect on the snowpack.

Weather Forecast

A ridge of high pressure brings dry and sunny conditions for the weekend. 

Friday Night: Clear, light N wind, freezing levels around 800 m.

Saturday: Sunny, light to moderate N wind, freezing levels reaching around 1500 m.

Sunday: Mainly sunny, moderate N wind, freezing levels potentially reaching around 2000 m in the late afternoon.

Monday: A mix of sun and cloud, moderate NW wind, freezing levels reaching around 1500 m.

Avalanche Summary

On Thursday, several persistent slab avalanches were reported up to size 2.5. Four of these were natural and the rest were human-triggered including one which was remotely triggered. Two of the naturals were on south aspects which were triggered by loose wet avalanches stepping down. Most of the rest of the activity was on northerly aspects. The majority of the activity appears to have occurred between 1600 and 2000 m elevation. Slab thickness was typically 30-70 cm and the failure plane was a combination of the mid-February and late-February weak layers which may be acting as more of a single thick weak layer. 

In addition to the persistent slab activity, a natural wet slab was observed on a south aspect at 1750 m and several natural wind slabs were observed. Numerous loose avalanches were observed from steep sun-exposed slopes. Explosives triggered one size 3 cornice. 

On Wednesday, a natural avalanche cycle up to size 3 was reported from the recent storm. A few skier controlled and remotely triggered (from as far away as 40 m) avalanches were also reported. These persistent slabs failed on the mid-February facet/crust interface buried approximately 50 cm down. They caught people by surprise, but no involvements occurred.  

Snowpack Summary

30-50 cm of wind-affected storm snow from earlier in the week sits over a variety of surfaces including sun crusts on solar aspects, a thick rain crust in windswept terrain and facets in shady, sheltered terrain. The recent storm snow has a decent bond in some areas, but a poor bond exists on northerly slopes (NW, N, NE, E) at treeline and in low alpine elevations (1600-2000 m) where the mid-February facet/ crust persistent weak layer has been touchy to human triggers. Whumpfing and remotely-triggered avalanches have been failing on a 3-5 cm thick layer of facets sliding on a hard melt-freeze crust. Some surfaces in windward alpine terrain have been scoured down to this firm crust.

Large and looming cornices have grown during the recent storm, primarily on north and east aspects. Periods of moderate northerly wind on Saturday may develop new wind slabs. 

Terrain and Travel

  • Be aware of the potential for large avalanches due to the presence of a persistent slab.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.
  • Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet

Problems

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.

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.

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.