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Avalanche Forecast

Archived

Feb 12th, 2017–Feb 13th, 2017

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

Regions

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Warming and sunshine Monday will make loose-wet, wet slab and cornice failures increasingly likely.  Be cautious of overhead hazard such as cornices. 

Detailed Forecast

Sunshine and very mild temperatures with light to moderate ridgetop winds are expected Monday. Freezing levels should near 8000 feet by later Monday.  

Older wind slabs should have settled and stabilized by Monday, but watch for signs of wind deposited snow on specific terrain features such as steep N-SE facing slopes below ridges.

Sunshine and very mild temperatures Monday should make loose-wet avalanches possible on steep southerly slopes facing the sun. Be cautious on sun exposed slopes if the wet surface snow becomes more than a few inches. There is also the possibility of any loose-wet avalanches to trigger wet slab avalanches, which would be much more dangerous.

Recent cornices have become quite large and sunshine and warming Sunday will make cornice fall increasingly likely, especially during the warmest part of the day.

Snowpack Discussion

Weather and Snowpack

The last strong storm cycle began Wednesday 2/8 and peaked on Thursday 2/9. This storm cycle deposited 2-2.5 inches of water equivalent in the Cascade East - North zone. The warming peaked Thursday afternoon, but precipitation remained snow throughout the event at all elevations in the Washington Pass area depositing 2-3 feet of snow including snow showers Friday. Westerly winds became strong late Thursday into Friday building wind slabs and cornices.

A dry day Saturday with filtered sunshine through high clouds began the settlement and stabilization process.

Building high pressure Sunday brought increasing sunshine and warming temperatures, with about 6 inches of snowpack settlement by Sunday afternoon, allowing for a decreasing danger.

Recent Observations

North

NWAC's Jeff Ward covered a significant amount of terrain in the Washington Pass zone Sunday. The few days of snowpack settlement, warming and sunshine have allowed for the 2-3 feet of recent storm snow to stabilize significantly by Sunday.  Snowpack tests were negative Sunday and no triggered avalanches occurred.

The avalanche problems are shifting away from storm related problems to warming and sunshine related dangers. A very large cornice failed naturally Sunday and will be added in the problems list.  

The heavy storm cycle was a great snowpack test for any Persistent Weak Layers that we have not had good confirmation about. There was no evidence of any deeper releases as a result of the recent cycle and as such we will remove the Persistent Slab from the problem list.

Central

A large avalanche off of Dirty Face Peak knocked in a garage door of a house on the north shore of L. Wenatchee around 1130 am Thursday. 

NWAC's Tom Curtis travelled in the Icicle Creek area near Cashmere Mountain Saturday. Tom did not get far as there was only a dusting of recent snow over a slick, firm crust. The greatest danger in this area was from uncontrolled falls on the slick crust as opposed to avalanches. Observations were not made in higher elevation terrain where wind slabs may have formed.

South

No recent observations since Tuesday. 

Problems

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.

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.