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Avalanche Forecast

Archived

Feb 28th, 2015–Mar 1st, 2015

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

Regions

Mt Hood.

Winds slabs will be less likely, but remain the primary concern Sunday and should generally be found on non-traditional westerly aspects, especially below ridges. Careful route finding and attention to local loading patterns will be necessary to have a safe and enjoyable day in avalanche terrain.

Detailed Forecast

Mostly sunny Sunday with increasing high clouds late, remaining cool with light winds. This should allow for further settlement of any recently formed wind slabs. Winds slabs will remain the primary concern Sunday, so pay attention to the recent local loading pattern in your area, but generally expect non-traditional westerly aspects to be the most suspect. Wind slabs may have formed further downslope of areas of stronger winds, a fact that may not be apparent until you've already committed to a slope.  

Loose wet avalanches on steeper solar slopes should be possible during the warmest part of the day and on direct solar aspects. The sun is strong enough moving into early March to activate loose wet avalanches even on cooler days. 

Due to the low snowpack, especially below treeline, watch for terrain hazards such as open creeks, partially covered rocks and vegetation. Many areas below treeline do not have enough snow (new or existing) to pose an avalanche hazard. 

Snowpack Discussion

A wet start to February was followed by mostly fair weather through mid-February, leading to generally thick surface crusts, as well as further deterioration of the snow cover below treeline. Weak weather disturbances last week produced light snowfall, but no new avalanche concerns. 

New snowfall at NWAC Mt. Hood stations from Wednesday night through Thursday afternoon ranged from less than 1 inch at Meadows to a soggy 3 inches at Timberline with likely higher accumulations and some loading of easterly aspects above treeline. 

A low pressure system brought variable amounts of new snow to Mt. Hood on Friday and Friday night, with Timberline receiving roughly 6 inches, with about 4 inches at Mt. Hood Meadows. Still, this was enough to build sensitive new wind slab Friday morning at about 6600 ft on a NE aspect at Meadows, with soft wind slabs around 1 ft easily releasing. 

The winds shifted and became very strong from the E-NE Friday night and Saturday, especially above about 6500 feet where much of the recent surface snow has likely been stripped from most slopes. The winds were so strong to likely have blasted the shallow surface snow to who knows where, rather than steadily building new wind slab layers. However, keep an eye out for isolated pockets of wind slab that may have formed on a variety of terrain features.  

The mid and lower snowpack at Mt Hood snow consist of layers of stable consolidated rounded grains or melt forms and crusts from multiple warm periods this winter.

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.