Avalanche Forecast

Archived

Apr 3rd, 2023–Apr 4th, 2023

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 possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Below Threshold.

Regions

Yukon, Tutshi, Wheaton, White Pass East, White Pass West.

Wind slabs persist at higher elevations.

Seek out terrain hidden from the wind and keep an eye on the solar effect if the sun pokes out.

Confidence

Moderate

Avalanche Summary

In White Pass, there were reports of wind transport during the day on Sunday creating reactive wind slabs. A skier triggered one while boot-packing in the alpine on a north aspect. It was up to 30 cm deep. A similar story was playing out in Haines Pass as well.

There was a skier remote triggered (from a distance) cornice fall which subsequently triggered a size 3 persistent slab avalanche on a northeast aspect at 1750 m on Saturday. The trigger point was at a thin spot on top of a flat ridgetop. The fracture was 200 cm deep and was suspected of running on a layer of facets sitting on a crust buried in January.

Let us know what you are seeing by submitting a report to the Mountain Information Network.

Snowpack Summary

Slopes facing the sun are likely moist or have a thin surface crust. 5 to 15 cm of new snow falling late last week sits on wind-pressed surfaces in the alpine. Soft older snow may be found in shady, wind-sheltered areas. A weak layer of surface hoar/crust/facets buried in early January is now over 1 m deep in most areas and was responsible for an avalanche release recently. The lower snowpack consists of basal facets, particularly in thin snowpack areas.

Weather Summary

Monday Night

Clear, no accumulation, southwest 10 km/h ramping 30, alpine temperature around -10 °C.

Tuesday

A mix of sun and cloud, trace accumulation, winds southwest 40 to 50 km/h, alpine temperature around -12 to -8 °C.

Wednesday

A mix of sun and cloud, trace to 2 cm accumulation, winds southwest 40 km/h, alpine temperature -4 to -10 °C.

Thursday

A mix of sun and cloud, 10 to 15 cm accumulation starting Wednesday evening and carrying through the day, winds southeast 40 to 50 km/h, alpine temperatures -6 °C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

Carefully evaluate steep lines for wind slabs.
Use caution on large alpine slopes, especially around thin areas that may propagate to deeper instabilities.
Pay attention to cornices and give them a wide berth when traveling on or below ridges.
Watch for wind-loaded pockets especially around ridgecrest and in extreme terrain.

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.