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Avalanche Forecast

Archived

Mar 14th, 2015–Mar 15th, 2015

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

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It's a tricky forecast but in general expect increasing avalanche danger with elevation. 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. An easterly component should help enhance precipitation along the east slopes Sunday. W through E aspects (clockwise) should become loaded near and 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 near the Cascade crest.  

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. The North Cascade Mountain Guides were in the Harts Pass and Washington Pass area last weekend. They reported some cool varied surface snow on north slopes, corn snow on south slopes, and no stability concerns. The snow study plot on a north aspect at 6600 feet above Varden Creek measured a snow depth of nearly two and a half meters. 

NWAC observer Jeff Ward was in the Hart's Pass area of the northeast Cascades Friday and reported isolated and very small wind slab not bonding well to the underlying crust above 6500 ft. 

On Saturday, the most significant weather system this month brought new precipitation with snow level mainly between 6000-7000 feet. 24 hr water accumulations at NWAC stations east of the crest were up to 1.0 inches ending 4 pm Saturday, with much lower totals in the Blewett-Mission Ridge area.  The Hart's Pass snotel picked up a few inches of new snow before temperatures settled in the mid 30s during the afternoon. 

There have not been any reports of significant avalanches in the Cascades for many days. There was nearly no snowfall January to so far in March near and below treeline. The snowpack at low elevations remains meager to non-existent.

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.