Bollettino valanghe

North Columbia

Feb 20 – 21, 2022Avalanche Canada
Vedi sulla mappa
Archiviato · scaduto 5 years ago

Pericolo valanghe

Tue
Wed
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
Apri la mappa completa

In sintesi

Storm slabs are expected to remain reactive to human triggering, especially in wind-loaded terrain.

Forecast will be updated at 6:30AM (PST) if overnight snowfall exceeds forecast.

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely - Possible
    Dimensione
    1.5–3

    A weak layer formed in late January may be found 50 to 150 cm deep in the snowpack. This layer consists of faceted snow, a sun crust on steep solar aspect, and most notably large surface hoar crystals in sheltered terrain.

    Reactivity on this layer has tapered, but a significant amount of new load may cause this layer to 'wake up'.

    The most reactivity on this layer has been seen between 1600-2200 m in open areas in the trees, in cut blocks, and on steep convexities. Terrain features to be suspect of include the lee side of ridges, openings in trees, cut blocks, and burns, especially on northerly aspects where the layer may not be capped by a firm crust.

  • Storm Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    1–2.5

    30-100 cm of recent storm snow overlies the February 15th drought layer. Storm slab reactivity can be expected to persist into Sunday, especially on leeward slopes where deeper, and stiffer slabs exist due to wind loading. 

    Dry-loose avalanches may be seen from steeper slopes, especially where a firm crust exists below the new snow. 

Confidence

Moderate - Forecast precipitation (either snow or rain) amounts are uncertain. Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

Precipitation will taper on Sunday. Following a familiar pattern, arctic air reinvades the province bringing cold temperatures and clear skies by Monday.

Saturday Overnight: Continued snowfall, trace to 5cm accumulation. Freezing level dropping to valley bottom, alpine temperatures around -10 C. Light to moderate northwesterly winds. 

Sunday: Mainly cloudy, light snowfall. Alpine temperatures around -12 C. Light northwesterly winds. 

Monday: Partially cloudy. Alpine temperatures around -20 C. Light to moderate northeasterly winds.

Tuesday: Mainly clear. Alpine temperatures around -20 C. Light to moderate northeasterly winds.

Avalanche Summary

Human-triggered storm slab avalanches are likely on Sunday.

On Friday, numerous natural and human-triggered storm and wind slabs were reported throughout the region. Most of these avalanches were relatively small and shallow. Some of the results ran on the February 15th drought layer, while others failed on density changes within the new storm snow.

Explosive control in the past week has initiated some larger persistent slabs up to size 3. Human-triggering on this layer has tapered, but we would continue to be cautious as the snowpack adjusts to new load.

Snowpack Summary

Saturday's 15-40 cm of new snow will add to this week's snowfall with 30-120 cm now overlying the old, hard surface. This drought layer was formed during a period of high pressure in mid-February. The layer is comprised of facetted snow, a melt-freeze crust at lower elevations, a sun-crust on steep solar aspects, and hard wind-affected snow in the alpine and exposed treeline. 

Digging deeper in the snowpack, several weak layers exist in the upper snowpack including buried crusts, facets, and a prominent weak layer of buried surface hoar. This surface hoar has been the dominating feature in the past few weeks and is most prominent in sheltered openings at and below treeline. Reactivity on this layer has begun to taper, but we would continue to be cautious as the snowpack adjusts to new load.

The facet/crust layer that formed in early December is now buried around 150 to 250 cm. The last reported avalanche was on January 31 from a large explosive, and before that on January 23. Although unlikely, the layer could be triggered from a large load like a cornice fall or a shallower slab avalanche could step down to this layer. 

Terrain and Travel

  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Closely monitor how the new snow is bonding to the old surface.
  • Use small low consequence slopes to test the bond of the new snow.
  • Shooting cracks, whumphs and recent avalanches are strong indicators of an unstable snowpack.

Regioni coperte