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Avalanche Forecast

Archived

Jan 3rd, 2015–Jan 4th, 2015

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

Mt Hood.

The avalanche danger will increase sharply by late Sunday afternoon and evening with human triggered slides becoming likely. Choose a conservative travel plan and make sure your plan allows for a safe exit if conditions deteriorate quicker than expected. 

Detailed Forecast

Light snowfall Saturday night and Sunday morning will increase in intensity Sunday afternoon along with increasing winds. A warming trend should lead to inverted storm snow by later Sunday afternoon. Snow should change to rain at lower elevations. 

Natural loose wet avalanches will become very likely on steeper slopes below treeline with the change to rain Sunday afternoon. 

Shallow storm slab avalanches may bond poorly within storm layers or to the underlying crust. New wind slab should form on N through SE aspects near and above treeline.

All of this will lead to increasing avalanche danger Sunday. Expect human triggered avalanches to be likely as the afternoon wears on. Be prepared to curtail your trip early if conditions become sensitive earlier than forecast. 

More significant warming and precipitation is expected Sunday night and a natural avalanche cycle is expected. 

Snowpack Discussion

A storm system hit the Northwest last weekend with strong west to northwest winds. NWAC sites at Mt Hood picked up about 2-3 ft of snow with a good cooling trend. However, strong northeast winds hit at the tail end of the storm Monday and Tuesday. This transported recent storm snow and formed some local wind slab on non-traditional lee aspects near and above treeline. 

An upper ridge over the coastal waters tilted inland Wednesday and Thursday producing sunny weather and warm temperatures at higher elevations. This may have caused some snowballing and wet loose avalanches on steep slopes facing the sun at Mt Hood. Mt. Hood Meadows pro patrol reported light snow remaining on sheltered slopes below treeline. They also confirmed the unusual wind direction earlier in the week had scoured traditional lee aspects.  One of our biggest concerns heading into the upcoming weekend storm will be the new storm snow's ability to bond to a variety of snow surfaces; near surface facets, wind board, melt-freeze crusts, etc.  

A generally strong mid and lower snowpack is expected at Mt Hood.

Problems

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.

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.

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.