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Avalanche Forecast

Archived

Mar 19th, 2012–Mar 20th, 2012

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

Regions

Northwest Inland.

Confidence

Fair - Forecast snowfall amounts are uncertain

Weather Forecast

Tonight and Tuesday: Moderate snowfall - Approximately 5cm overnight and an additional 5-10cm on Tuesday. The freezing level (FL) is around 500m and winds are moderate from the S-SW. Wednesday: Unsettled conditions with convective flurries - 5cm. FL is near 500m. Winds easing to light from the south. Thursday: Mainly cloudy with light flurries. No significant accumulation.

Avalanche Summary

The soon to be buried snow surface includes a sun crust on southerly aspects, surface facets or surface hoar in cool shady areas, and pockets of wind slab in exposed terrain. The mid February persistent weak layer interface, comprised of spotty surface hoar, facets and crusts, is buried 80-120 cm below the surface. No recent activity has been reported on this interface. However, recent snowpack tests have been giving hard but sudden "pop" results and indicate it is has the potential to react given the right trigger in the right place. For route selection, it should still be on your radar and is more likely to be triggered on steeper, unsupported terrain. Cornices in the area are reported to be very large and primed for natural collapse or triggering by a person.

Snowpack Summary

No new slab avalanches have been reported in the past day or two. There were a few reports of cornice failures, but most did not trigger slabs.

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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.

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.