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Avalanche Forecast

Archived

Mar 12th, 2014–Mar 13th, 2014

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

Regions

Olympics.

Watch for further spring snow and avalanche conditions on Thursday. If wet snow becomes deeper than a few inches it is time to head to shallower angled terrain well away from large open slopes.

Detailed Forecast

A refreezing of surface snow on solar aspects is likely in most areas on Wednesday night.

Then partly or mostly sunny weather but with slightly cooler temperatures is expected on Thursday.

But spring sun angles and power are increasing and should re-melt surface to some extent on solar slopes again on Thursday.

This should make further human triggered wet loose avalanches possible mainly on direct solar slopes by the afternoon. Watch for pinwheels and surface wet snow deeper than a few inches.

Cornice releases should remain possible on Thursday. Avoid walking onto or below cornices on or below ridges.

Areas of old wind slab may still be possible on lee slopes above treeline at higher elevations. Watch for signs of older firmer wind transported snow.

Snowpack Discussion

Over the past month two major storm cycles moved across Northwest.

The first two week storm cycle ended February 25th and deposited about 9 feet mostly wet heavy snow at Hurricane and caused avalanches across the region.

The second week long storm cycle wound down last Sunday and produced similar water equivalents as the February cycle.  Water equivalents and snowfall for the the second cycle were about 4 inches and 2 feet at Hurricane. So this was a cycle of wet snow and rain. This produced avalanches again across the region including reports from Holden Village, Stevens Pass, Tumwater Canyon, Alpental and Snoqualmie with pass closures at times.

NWAC observers Tyler and Katie Reid on Friday at Hurricane reported wet and saturated upper snow pack layers but with no positive snow pit test results and numerous wet loose avalanches to size 2. Warming effects had penetrated quite deeply into upper snowpack layers. Here is a video from Tyler and Katy at Hurricane on Friday.

Warm wet weather last weekend caused wet snow conditions and many wet loose avalanches at Hurricane with several cornice collapses as well as reported by NWAC observer Katy Reid on Sunday.

A cycle of night time re-freezing and daytime melting is reported from the Cascades Tuesday and Wednesday with similar conditions expected at Hurricane.

Problems

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

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.

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.