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Avalanche Forecast

Archived

Feb 10th, 2017–Feb 11th, 2017

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

Mt Hood.

Strong winds Friday and Friday night will have built fresh wind slab on lee aspects mainly near and above treeline. Watch for new wind slab in the upper portion of the below treeline band. Easterly aspects will be highlighted in the elevation/aspect diagram but watch for firmer wind transported snow on a variety of aspects.

Detailed Forecast

Light to moderate showers Friday night should taper off after midnight with only isolated light snow showers expected on Saturday. The same trend is expected for the moderate to occasionally strong W winds forecast for Friday night with winds easing considerably on Saturday.

Strong winds Friday and Friday night will have built fresh wind slab on lee aspects mainly near and above treeline. Watch for new wind slab in the upper portion of the below treeline band. Easterly aspects will be highlighted in the elevation/aspect diagram but watch for firmer wind transported snow on a variety of aspects.   

Despite the cooling trend, new and shallow storm slab instabilities may be locally sensitive. 

Snowpack Discussion

Weather and Snowpack

A strong storm cycle Friday 2/3 through Monday 2/6 produced about 3-4 feet on Mt Hood. 

A strong plume of moisture brought light to moderate rain to Mt. Hood Wednesday afternoon through Thursday. About 2 inches of water fell mainly as rain at Mt. Hood from Wednesday afternoon through Thursday afternoon with significant snowpack settlement. A strong cold front swept through around 2 pm Thursday followed by bands of light showers in SW flow along with the start of a slow cooling trend.  

Friday was windy with a slow cooling trend during the day. Light showers increased and generally became moderate in the evening. The Mt. Hood Meadows station had received 6 inches of snow through 7 pm Friday.  

Recent Observations

On Thursday, Meadows pro-patrol reported saturated snow down 25 cm but no avalanche activity in the ski area. The upper mountain was not observed due to strong winds and limited visibility. 

By Friday morning Meadows pro-patrol reported widespread loose wet and small wet slab natural activity that had occurred Thursday near and above treeline. One very large wet slab occurred in the God’s Wall path up to size D3, likely releasing sometime Thursday.  Below treeline, a saturated snowpack was still re-freezing and became less supportable at lower elevations.  

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.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.