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Avalanche Forecast

Archived

Apr 20th, 2024–Apr 21st, 2024

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

Regions

Banff Yoho Kootenay, Little Yoho, Banff, East Side 93N, Kootenay, Lake Louise, LLSA, Sunshine, West Side 93N, Field.

Increasing winds and snow will contribute to slab development into the start of the week.

Watch for fresh slabs over crusts on solar aspects as well as further development of the existing slabs on shaded slopes.

Confidence

Moderate

Avalanche Summary

Over the last couple of days some small thin, fresh windslabs and sluffs have been triggered in the surface snow in the alpine.

Friday and Saturday, loose wet avalanches were generated as the recent snow became wet in steep terrain over previous crusts.

The recent cool temperatures have temporarily slowed down the deeper avalanche activity.

Snowpack Summary

5-15 cm of recent snow is likely now capped by sun crusts. On north aspects this snow sits over dry snow above 2200m. Isolated wind slabs are found in the alpine, these will build, and wind effect will spread to treeline as winds increase.

In the mid-pack, the Feb 3 persistent layer (crust / facets) remains a concern in thin areas on northerly alpine aspects near 2300m and above where no crusts have formed to date. Below this, facets and depth hoar comprise the lower snowpack.

Monday

  • 5-15 cm of recent snow is now likely to have crusts on all but north aspects where it sits over dry snow above 2200m. Wind effect treeline and above

In the mid-pack, the Feb 3 persistent layer (crust/facet layer) remains a concern on northerly alpine aspects near 2300m and above where no crusts have formed to date.

Tuesday

  • 5-15 cm of recent snow is now likely to have crusts on all but north aspects where it sits over dry snow above 2200m. Wind effect treeline and above

In the mid-pack, the Feb 3 persistent layer (crust/facet layer) remains a concern on northerly alpine aspects near 2300m and above where no crusts have formed to date.

Weather Summary

Saturday Overnight: Winds increase: moderate to strong SW. Freezing Levels near 1500m. Snow begins as a cold front passes.

Sunday: Light snow accumulation: 5 cm. Freezing level to approx 1800m. Winds: west, strong.

Monday: Winds diminish, cloudy with some potential for flurries. Freezing levels rise to near 2000m. Clearing overnight.

Tuesday: Warming, freezing levels approaching 2500m.

Terrain and Travel Advice

  • Watch for wind-loaded pockets especially around ridgecrest and in extreme terrain.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
  • Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.

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.

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.