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Avalanche Forecast

Archived

Mar 11th, 2018–Mar 12th, 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.

Warm and sunny weather will continue to cause wet snow conditions Monday in the Olympics. Avoid slopes where even small avalanches may have large consequences such as above cliffs, creeks, and rocks. Weak older snow exists in the snowpack. This is a classic low likelihood-high consequence scenario. To avoid large persistent slabs, stay off of steep large open slopes that may still harbor this difficult to predict and manage avalanche problem.

Detailed Forecast

Wet snow will develop with continued sunshine and warm air temperatures creating conditions for wet avalanches. This will happen first on steep rocky slopes receiving direct sun but will spread to all aspects as air temperatures warm. A poor overnight refreeze will allow this process to occur faster on Monday. Stay away from slopes where even a small loose wet avalanche may have higher consequences such as above cliffs, gullies, and creeks.

Several deeper persistent weak layers have been reported in the snowpack. The exact weak layer and depth depends on your aspect and elevation. This can be a classic low likelihood-high consequence scenario. To avoid persistent slabs, stay off of large open slopes where these larger avalanches may occur. While they are difficult for a person to trigger, a small avalanche such as a loose wet or cornice fall may trigger these deeper layers. 

Limit your exposure to overhead cornices as you travel. They could fail without warming due to daytime warming and sunshine.

Snowpack Discussion

Temperatures gradually warmed over the weekend, topping out in the mid-40s at Hurricane Ridge Sunday afternoon. 

Three to four inches of snow fell in the Olympics Thursday night into Friday. Winds during the storm redistributed the new snow on exposed areas near and above treeline. This soft snow is the most susceptible to impact by warm temperatures and sunshine.

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 other than small wet loose on steep sunny slopes.

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

Observations

On Sunday as of 1 PM, NPS rangers reported generally small loose wet avalanches with one larger release caused by a partial cornice collapse. 

On Saturday, Forecaster Robert Hahn and NPS Rangers found the 2/8 weak snow/crust interface in snowpits on a West aspect at 5300' and down 2.5 feet from the surface. No new avalanche activity was observed other than small wet loose avalanches on steep sunny slopes. North facing terrain still held drier settled powder. 

On Wednesday March 7th, a NPS ranger traveled in the Victor Pass area and found many crusts with facets forming on south aspects. Near ridge-tops, the 2/13 weak layer 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.

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.