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Avalanche Forecast

Archived

Jan 27th, 2018–Jan 28th, 2018

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

Regions

Olympics.

Warm wet weather Sunday will cause a drastic change in snow conditions and avalanche problems. Wet avalanche conditions will develop well into the near treeline area and be very difficult to predict and manage. Chose conservative terrain well away from steep open slopes where these avalanches may initiate.  

Detailed Forecast

Avalanche hazard will continue to increase and avalanche problems will change character on Sunday.  Above freezing air temperatures and rain will extend well into the near treeline band. Wet avalanches will result from this drastic warm-up.

Wet avalanches can be very difficult to predict. The exact timing and size of these avalanches depends on numerous weather and snowpack factors. Resulting avalanche may be large and destructive. Avoid traveling on or near terrain where avalanche might start.

Above treeline continued snow and wind will build on already deep wind slabs. It will be very difficult to travel safely above treeline due to a continually increasing hazard.

Chose conservative terrain Sunday away from steep open slopes where avalanche may initiate. Use extra caution traveling through areas where avalanches may run and stop. Any avalanche occurring Sunday may entrain significant amounts of snow causing them to become larger and run farther than you might normally expect. Avalanches may travel into common travel routes. 

Snowpack Discussion

A very active stormy period continued to impact the Olympic Mountains Saturday. Warm air temperatures, additional snow, and strong southerly winds formed deep wind slabs on lee slopes.

Winds throughout the storm cycle reshaped the landscape near and above treeline creating a variety of snow surfaces. Scoured crust, firm wind slabs, and soft snow can all be found depending on location.

Below treeline Saturday, warming air temperatures and light rain created wet surface snow conditions.

Observations

NPS rangers reported several natural avalanches 

On Friday pro-observer Matt Schonwald reported on the tremendous change in the snowpack since this storm cycle began. Southerly winds plus nearly continuous snowfall sculpted the landscape near and above treeline. Large and very easy to trigger cornices, deep wind rolls and huge snowdepth variations were observed. Snowdepth on a south aspect at 5000' measured 120 cm vs. 370 cm at the same elevation on a northerly lee aspect.

Problems

Wet Slabs

Wet Slab avalanches are the release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slabs can be very unpredictable and destructive.

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.