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Avalanche Forecast

Archived

Feb 29th, 2016–Mar 1st, 2016

Alpine
Natural and human triggered avalanches likely.
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.

Very dangerous avalanche conditions are expected to develop late Monday night with the danger decreasing during the day on Tuesday. Travel in avalanche terrain is not recommended Tuesday especially above treeline.   

Detailed Forecast

The avalanche danger will increase rapidly Monday night as warm frontal precipitation spreads over the area and increases during the early morning hours. Winds will also increase Monday night and stay elevated through Tuesday.    

Storm slab instabilities should develop during intense precipitation periods and due to the overall warming trend Monday night. A natural avalanche cycle will likely occur Monday night with the danger decreasing during the day as precipitation tapers down and rising snow levels plateau. 

New wind slab should develop mainly above treeline on N through SE slopes. Loose wet avalanches will become very likely on steeper slopes in areas that see a switch to rain. Avalanches that begin in the new snow may become larger as they entrain or step down to snowfall received Sunday and Sunday night. 

Very dangerous avalanche conditions are expected to develop late Monday night with the danger decreasing during the day on Tuesday. Travel in avalanche terrain is not recommended Tuesday especially above treeline. 

 

Snowpack Discussion

Weather and Snowpack

Springlike weather under high pressure Wednesday and Thursday of last week led to abundant sunshine with daytime highs climbing into the 40's and 50's. The fair and mild weather caused thick surface crusts, especially on solar slopes in most areas by Friday and helped stabilize wind slab formed early last week. 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 mid-day Sunday. A few inches of wet snow accumulated through the afternoon at Mt. Hood stations, but the strong winds were the main story. The most 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)! 

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

The Mt Hood Meadows pro-patrol on Saturday reported little accumulation of new snow and no significant new layers in the above treeline. A wet consolidated upper snow pack was seen in the near and below treeline. Cornice releases gave a couple some size 1 and 2 wind slabs on an east slope at about 6500 feet that is commonly wind loaded. 

No avalanches were observed on Sunday near and below treeline. Winds were too strong for any person not directly anchored to the mountain to make observations above treeline. 

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. 

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.

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.