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Avalanche Forecast

Archived

Mar 14th, 2015–Mar 15th, 2015

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

Regions

Mt Hood.

A mix of storm and loose wet avalanche problems are possible Sunday above treeline. 

Detailed Forecast

Sunday should be another stormy day as a low pressure system lifts precipitation north across the Cascades. Unfortunately for Mt. Hood, the snow levels look to start much warmer than the Cascades further north. 

There may be some loose wet or shallow storm slab concerns above treeline on Sunday, mainly on lee N through SE aspects. Rainfall near and below treeline rain is not expected to have much effect since the snowpack in these elevation bands are limited, consolidated, and draining well.  

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 to cause an avalanche danger.

Snowpack Discussion

The latest installment of warm and dry weather occurred from early March through midweek leading to more snowpack consolidation and a scarcity of avalanche activity. Reports indicated thickening surface crusts on most slopes and some corn snow development on solar slopes. An inch of new snow accumulated above treeline Thursday with rain below. 

On Saturday, the most significant weather system this month brought plenty of precipitation...but mostly in the form of rain with the snow level above 7000 feet. 24 hr rain accumulations at NWAC Mt. Hood stations were near 1.5 inches ending 4 pm Saturday. Significant new snowfall likely accumulated on the upper volcano Saturday above NWAC's forecast area. 

The snowpack at low elevations remains meager to non-existent. The mid and lower snowpack at Mt Hood consists of layers of stable consolidated rounded grains or melt forms and crusts from multiple warm periods this winter.

Problems

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.

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.