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Avalanche Forecast

Archived

Mar 23rd, 2014–Mar 24th, 2014

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

Regions

Olympics.

We suggest a conservative approach on Monday with the avalanche danger driven by warming temperatures, sunshine and the potential for wet snow avalanches. Wind slab avalanches should be less likely but still possible on lee aspects near and above treeline.  

Detailed Forecast

Monday should be the warmest day this week. Increasing mid and high clouds Sunday night may preclude a solid refreeze of the snow surface. Light rain or snow is possible for the Olympics early Monday morning, but should give way to mostly sunny or at least filtered sunshine by Monday afternoon with freezing levels 7000-8000 feet. 

The equinox has passed and we've officially moved into spring; wet loose avalanches remain possible on sun exposed terrain especially in the late morning and afternoon hours. Watch for wet surface snow deeper than a few inches, pinwheeling of surface snow and small natural wet loose releases that usually precede more major wet loose snow avalanches. Wet loose avalanches may be larger and entrain more snow than over the weekend due to the warmer temperatures and sun, and could in isolated areas step down to lingering slab instabilities weakened my meltwater in the upper snowpack.  

However, continue to watch for lingering but likely isolated wind slab generally on lee north through easterly slopes near and above treeline. Watch for cracking or firmer wind transported snow in steep exposed terrain. A large cornice fall could provide the right natural trigger for a wind slab to release on a lee slope. Cornices should be more likely to fail on Monday, and should be given a wide berth.

Snowpack Discussion

The last significant frontal boundary was stalled over the Olympics and north Cascades Saturday afternoon before finally sagging south last Sunday, with rain generally changing to snow in a north to south fashion across the area.  A favorable temperature trend with a gradual cooling occurred with this storm. The NWAC site at Hurricane picked up about 13 inches of snow late Saturday through Monday and produced wind slab layers on north through east aspects near tree line and allowed for one skier triggered soft slab Sunday afternoon that covered the road. 

The latest cold front crossed the Northwest on Wednesday. This system produced more snow in the Cascades with the Hurricane Ridge weather station recording only about 4 inches of new snow at low temperatures and with generally light winds.  On Friday afternoon NWAC observer Katy Reid reported a thin melt-freeze crust over this most recent storm snow and denser wind slab on N thru SE near treeline that was stubborn in stability tests and not noted in any recent avalanches.  She also observed widespread surface hoar from Thursday night (and probably Friday night) along with graupel as being preserved under cool temperatures and light winds but this was reported as destroyed by the end of the weekend. 

On Sunday Katy reported numerous and generally small with a few larger wet loose avalanches on solar aspects but dry loose naturals on due northerly aspects at higher elevations.  She also found wind slab in the limited above treeline zone near Hurricane Ridge to be more sensitive and prone to snowpit test failures down 20 cm and poorly bonded to melt-freeze crust on the colder N-NE aspects.  

Increasing clouds and periods of light rain or snow were seen on Saturday with mostly sunny skies and moderate freezing levels on Sunday.  

Katy reported the lower and mid snowpack near treeline as generally well consolidated melt forms.  

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.