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Avalanche Forecast

Archived

Feb 24th, 2018–Feb 25th, 2018

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

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Very dangerous avalanche conditions have developed by early Saturday. Natural or triggered avalanches are very likely. These avalanches will run fast and over long distances. These conditions are not limited to higher elevations, but extend well below treeline. Travel in avalanche terrain is not recommended Saturday. 

Detailed Forecast

Updated 0830 Saturday... 

Mt Baker pro patrol report widespread sensitive natural or triggered slab avalanches Saturday morning, including sympathetic releases widely propagating with avalanches running fast and long distances.

Light snow showers and moderate crest level winds will continue to re-distribute weak surface snow and build further areas of wind slabs near ridges Saturday. Cold temperatures will maintain very sensitive storm snow weak layers. Natural or triggered slab avalanches are very likely Saturday. These avalanches may propagate wide distances and run fast and farther then expected. Backcountry travel in avalanche terrain is not recommended Saturday. 

Previous forecast... 

A persistent slab problem will continue Saturday in the Mt Baker area. Conditions this past week have not allowed this dangerous weak layer to sufficiently heal. A higher degree of spatial variability exists on this layer in the Baker area. However, it can be very difficult to determine exactly where this layer is and is not present. Snow profiles and snowpack tests can confirm the presence of this layer but cannot prove its absence. Continue to stay off of large steep open slopes where you may trigger this avalanche.

Snowpack Discussion

Updated 0830 Saturday...

12-14 inches of new storm snow accumulated by Saturday morning. The new wind stiffened storm snow fell on very weak surface snow that caused widespread natural avalanches Saturday morning. Sympathetic avalanche releases were reported, propagating wide distances and running very fast and far. Winds and denser storm snow over a shallow weak low density snow layer is making for very sensitive and dangerous avalanche conditions. 

Previous discussion...

Moderate to strong winds Friday afternoon began to transport loose surface snow forming new wind slabs on lee aspects. The upper snowpack consists of 2-4 feet of soft settled snow. In some locations this snow sits on top of weak sugary facets. These facets can be located just above the most recent (2/8) crust layer. Several avalanches, collapses, and whumphs have been triggered on this persistent weak layer in other areas of the west slopes of the Cascades. Snowpack tests and observations from around the west slopes of the Cascades continue to demonstrate that this layer can fail and produce avalanches.

A high degree of spatial variability exists in the Mt Baker area where the facet layer has been found but is more localized.

Below the 2/8 crust there are no significant layers of concern.

Observations

North

Updated 0830 Saturday... Mt Baker pro patrol report widespread sensitive natural or triggered slab avalanches Saturday morning, including sympathetic releases widely propagating with avalanches running fast and long distances.

Professional observations from the Mt Baker area report a high degree of spatial variability in the location of the weak facet layer. 

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.

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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.