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Avalanche Forecast

Archived

Mar 9th, 2018–Mar 10th, 2018

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

Olympics.

Loose wet avalanches are most likely to occur on steep sun exposed slopes Saturday. Stay off of these slopes as the sun comes out and warms up the surface snow. Lingering wind slabs can still be found on exposed features at higher elevations. Both of these avalanche problems overlay old weak snow in some locations. Avoid large open slopes greater than 35 degrees that may hold this difficult to manage avalanche problem.

Detailed Forecast

Sunny skies will allow wet surface snow conditions to develop Saturday. Expect roller balls and pinwheels as the snow surface warms. This will happen first on steep rock slopes receiving direct sun. Stay off of steep sunny slopes during the day where you may trigger a loose wet avalanche. While these avalanches are expected to be small, they may carry you into areas with higher consequences such as over cliffs, into rocks, or into gullies.

Small isolated wind slabs formed Thursday night with the new snow. Use visual clues such as snow drifts and fresh cornices to identify and avoid slopes where wind loading has occurred. You are most likely to find these slopes on northerly aspects near and above treeline.

Several potential persistent slab weak layers may be found depending on location. A high level of uncertainty exists in the Olympics around this difficult to predict and manage avalanche problem. This is classic low likelihood-high consequence scenario. So, give these slopes a wide berth. To avoid persistent slabs, stay off of large open slopes over 35 degrees where these avalanches can start. Smaller avalanches may step-down into these older snow layers creating large avalanches. Snow profiles and snowpack tests are the primary means to identify persistent weaklayers. While these observations can indicate the presence of a weak layer, they cannot prove its absence.

Snowpack Discussion

Three to four inches of new snow fell around the Olympics Friday. This new snow likely fell on a newly formed rain crust up to near treeline elevations. Generally south winds transported the new snow potentially forming shallow wind slabs on lee aspects.

Older weak snow layers continue to be reported in the Olympics. On slopes that receive direct sun several facet/crust layers may be found. A more widespread layer of weak sugary facets was found just above a very firm melt-freeze (2/8) crust formed in early February. The depth to this weak layer depends on aspect and elevation.

We have not received reports of recent avalanches in the Olympics.

There are no significant layers of concern below the 2/8 crust layer.

Observations

On Wednesday March 7th, a NPS ranger traveled in the Victor Pass area and found many crusts with facets forming on south aspect. Near ridge-tops, the 2/13 weaklayer was 8-12" down and 3 mm facets were observed. Mid-slope this layer was down 3-4 feet.

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.

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.