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Avalanche Forecast

Archived

Feb 24th, 2018–Feb 25th, 2018

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

Regions

Northwest Inland.

Wind slabs continue to build. Back off if you encounter drummy, hollow snow, whumpfing or recent avalanche activity.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

SATURDAY NIGHT: 5-10 cm snow. Strong south-westerly winds. SUNDAY: Mainly cloudy with light snow. Freezing level near 400 m. Moderate westerly winds.MONDAY: Mainly cloudy with light snow. Freezing level near 400 m. Strong westerly winds.TUESDAY: Mainly cloudy with light snow. Freezing level near 400 m. Moderate to strong westerly winds.More details can be found in the Mountain Weather Forecast.

Avalanche Summary

Rapid wind loading caused a natural avalanche cycle to size 2.5 on Wednesday. With ongoing moderate to strong winds forecast, wind slabs will remain possible to trigger over the next few days. Persistent slabs could still be triggered from thin-to-thick snowpack areas, or with a heavy load like a cornice fall.

Snowpack Summary

Light snow and strong winds over the weekend are building wind slabs in open terrain at alpine and treeline elevations. These overlie buried old hard wind slabs, scoured surfaces and sastrugi in many exposed areas. In wind-sheltered terrain, sun crusts or dry facets sit below the recent storm snow.The wind slabs sit on various old surfaces including sun crusts, facets and spotty surface hoar (which is most prevalent in sheltered treed locations). Around 50-150 cm down, you will find a crust/surface hoar layer from mid-January, which still has the chance to surprise you and could be triggered from a thin snowpack spot, or with a large trigger like cornice fall. Facets at the base of the snowpack can possibly be triggered from shallow snowpack areas.

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.