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Avalanche Forecast

Archived

Mar 16th, 2015–Mar 17th, 2015

Alpine
Natural avalanches possible, human triggered probable.
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

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It's nearly spring and the sun's strength and high water content of the new snow will make for a dangerous mix on steeper slopes near and above treeline where even a slow moving and shallow avalanche would be powerful and could force you into unintended terrain traps. 

Detailed Forecast

Partly to mostly sunny skies and a modest diurnal bump in afternoon temperatures should swap the greatest avalanche threat from lingering storm and wind slabs in the morning to a loose wet problems on solar aspects by Monday afternoon. Shifting winds should have cross-loaded a variety of aspects such that wind slab will not specifically be identified, but watch for local loading patterns. 

It's nearly spring and the sun's strength and high water content of the new snow will make for a dangerous mix on steeper slopes where even a slow moving and initially shallow avalanche would be powerful and could force you into unintended terrain traps. Changes in the snow will likely be rapid, so think about the avalanche hazard above and below while planning your route Monday.  

The avalanche danger will regionally be higher along the east slopes in the northeast Cascades. 

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 lasted from early to mid-March and led to more snowpack consolidation and a scarcity of avalanche activity. Snowdepths vary greatly across the east slopes... with a regionally healthy snowpack in the northeast Cascades to bare solar and low elevation slopes for the central and southeast Cascades.   

Over the weekend, an atmospheric river brought a one-two punch to the Pacific Northwest. Saturday's event brought up to 1.0 inches of water with a snow level around 6500 ft through Saturday afternoon, with much lower totals in the Blewett-Mission Ridge area. NWAC observer Jeff Ward was in the Hart's Pass area of the northeast Cascades over the weekend and reported touchy yet small loose wet near treeline and growing storm and wind slab concerns by late Saturday afternoon.

Another inch of water fell more evenly along the east slopes Sunday, with the snow level 6000 ft in the south and 4500-5000 ft in the north.  Around 10 inches (25 cm) fell at the NWAC Washington Pass and the Hart's Snotel through 4 pm Sunday. More snow is expected Sunday night.

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.