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Avalanche Forecast

Archived

Mar 14th, 2015–Mar 15th, 2015

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

Regions

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It's a tricky forecast but in general expect increasing avalanche danger with elevation and remember the NWAC forecast applies to elevations up to the Cascade crest (~7000 to 8000 ft). A mix of storm and loose wet avalanche problems are likely Sunday. 

Detailed Forecast

Sunday should be another stormy day as a low pressure system lifts precipitation north across the Cascades with snow levels in the morning starting lower than they have been in a long time and then slowly rising through the day.

The avalanche danger will be directly tied to the snow level, with increasing storm related avalanche danger with elevation. An afternoon increase in temperatures should also make loose wet avalanches involving morning snowfall possible. The heaviest precipitation during the daylight hours is expected from Stevens Pass and south with lighter amounts in the Mt. Baker area. NW through SE aspects should become loaded above treeline. 

It's a tricky forecast but in general expect increasing avalanche danger with elevation and remember the NWAC forecast applies to elevations up to the Cascade crest (~7000 to 8000 ft). Significant new snowfall was received near and above these elevations on Saturday.  

Below treeline rain is not expected to have much effect since the Cascade snowpack on these slopes beforehand is so limited, consolidated and stable. 

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, some corn snow development on solar slopes and a few reports of more winter-like surface conditions on northerly slopes at higher elevations. A few inches of new snow likely accumulated above 6000 ft from a weather system Thursday. 

On Saturday, the most significant weather system this month brought plenty of precipitation...but mostly in the form of rain with the snow level between 6000-7000 feet. 24 hr rain accumulations at NWAC stations were between 1.5 - 2.5 inches ending 3 pm Saturday. This may have led to some loose wet avalanches on non-solar aspects near and above treeline where pockets of preserved colder snow was present. 

The snowpack at low elevations remains meager to non-existent with the average snow-line around 4500-5000 ft along the west slopes. The mid and lower snowpack west of the crest consists of layers of stable consolidated rounded grains or melt forms and crusts from multiple warm periods this winter.

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.