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Avalanche Forecast

Archived

Mar 2nd, 2016–Mar 3rd, 2016

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

Mt Hood.

Heightened avalanche conditions are expected on specific terrain features, such as exposed lee slopes below ridges receiving wind transported snow.  Evaluate the snow and terrain carefully: identify features of concern.

Detailed Forecast

A period of moderate rain and snow at rising freezing levels is expected Wednesday night along with strong S-SW  ridgetop winds. Showers should taper quickly Thursday morning. A modest cooling trend is expected by early Thursday, however, the new storm related danger will continue through Thursday due to strong southwest winds loading lee slopes during showers Wednesday night. 

Storm slab instabilities should be stabilizing, but may still be sensitive Thursday. Wind slabs will continue to build Wednesday night on lee slopes, facing generally NW-NE.  Earlier formed wind slabs may still be reactive Thursday and may add to the increasingly complex snow structure, by Thursday.

Conservative terrain selection will be essential near and above treeline to avoid wind loaded terrain and features. Choose moderately angled terrain and avoid wind loaded slopes, saving those steeper lines for another day.

Non-avalanche hazard: Despite our seasonally healthy snowpack, many creeks are open and difficult to cross due to the periodic warm temperatures and rain events.  

Snowpack Discussion

Weather and Snowpack

Very mild weather a week ago allowed for the formation of a strong melt-freeze crust, especially thick on solar slopes in most areas by Friday. A weak front brought quite a bit of mostly rain to Mt Hood Friday night to Saturday morning.

A strong Pacific frontal system blew through the Cascades midday Sunday. Significant transport winds were from the W-SW and seen in the early afternoon post-frontal passage with gusts in the 40s or 50s near treeline with gusts recorded above 100 mph at the Mt. Hood Meadows Cascade Express station (7300 ft)! 

A warm front quickly dropped up to 6 inches of new snow early Tuesday morning at NWAC Mt. Hood stations before changing to rain. After a late morning lull, precipitation rates increased again in the afternoon as the cold front approached and snow levels began lowering. Not to be outdone by Sunday's system, gusts over150 mph were recorded at the Cascade Express station (7300') Tuesday afternoon! 

Wednesday was a transition day between storms with some early sunshine and mild temperatures and diminishing winds. 

The mid and lower snow pack along the west slopes should be a stable mix of crusts and layers of moist and rounded snow crystals.

Recent Observations

On Monday, Mt. Hood Meadows pro-patrol noted some 1-2' soft wind slabs on N-NE slopes above treeline during control work with very small storm slabs noted as well. 

Observations were limited Tuesday, but rain runnels were noted up to 6800 feet. At 6200', the top 30 cm of snow was wet. Mt. Hood Meadows pro-patrol noted 6-8" loose wet avalanches sensitive to ski cuts on steeper east aspects above treeline. 

The aftermath of the extreme wind event Tuesday was seen on Wednesday, with any exposed terrain stripped of recent snow, exposing a strong crust. The wind deposits were inconsistent and did not yield much in the way of avalanches, despite a healthy dose of bombs in the Mt Hood Meadows area. 

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.

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.