Avalanche Forecast

Archived

Apr 13th, 2023–Apr 14th, 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, human triggered possible.

Below Treeline

Below Threshold.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely.

Below Treeline

Below Threshold.

Regions

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

Lingering wind slabs may remain reactive to human triggers on lee aspects in the alpine.

Watch for signs of instability as you transition into wind-affected terrain.

Confidence

Moderate

Avalanche Summary

No new avalanches since this past Sunday when a size 2, cornice-triggered wind slab was reported on a north aspect in the alpine on Sunday. See MIN

On Saturday a rider triggered a cornice fall from a distance, which produced a size 3 persistent slab avalanche on a northeast aspect at 1750 m. The avalanche was 200 cm deep and was suspected of having failed on the layer of facets above a crust buried in January.

Observations are limited at this time of year, please consider sharing any information or photos you have on the Mountain Information Network to help guide our forecasts.

Snowpack Summary

20-30 cm of recent soft snow may have seen some redistribution by recent wind but above 1200 m, it remains largely available for wind transport. Below 1200 m, moist snow or a thin crust may exist at or near the surface.

The new snow sits over previously wind-affected snow on north and east facing slopes and a crust on south facing slopes.

A weak layer of surface hoar/crust/facets buried in early January is now buried over 1 m deep in most areas. This layer has produced recent avalanche activity and remains a concern in terrain where the snowpack is thin. The lower snowpack consists of basal facets, particularly in shallow areas.

Weather Summary

Thursday Night

Mostly cloudy; 2 cm / 25 to 25 km/h southwest ridgetop wind / Temperature at treeline around -5 C

Friday

Mostly sunny / 15 to 25 km/h southeast ridgetop wind / Temperature at treeline around -4 C

Saturday

Cloudy with flurries; 3-10 cm / 30-40 km/h southeast ridgetop wind / Temperature at treeline around -4 C / Freezing level 1000 m

Sunday

Mostly sunny; trace / 10-20 east wind / Temperature at treeline -3 C

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
Cornice failure may trigger large avalanches.
Use caution on large alpine slopes, especially around thin areas that may propagate to deeper instabilities.

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.