Avalanche Forecast
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.Â
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 avalanchesÂ
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.
Avalanche Problems
Wet Slabs
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 Slab avalanches can be very destructive.
Avoid terrain where and when you suspect Wet Slab avalanche activity. Give yourself a wide safety buffer to handle the uncertainty
A Wet Slab avalanche. In this avalanche, the meltwater pooled above a dusty layer of snow. Note all the smaller wet loose avalanches to either side.
Wet slabs occur when there is liquid water in the snowpack, and can release during the first few days of a warming period. Travel early in the day and avoiding avalanche paths when you see pinwheels, roller balls, loose wet avalanches, and during rain-on-snow events.
Elevations: Treeline, Below Treeline.
Likelihood: Likely
Expected Size: 1 - 1
Wind Slabs
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.
Wind Slabs form in specific areas, and are confined to lee and cross-loaded terrain features. They can be avoided by sticking to sheltered or wind-scoured areas..
Wind Slab avalanche. Winds blew from left to right. The area above the ridge has been scoured, and the snow drifted into a wind slab on the slope below.
Wind slabs can take up to a week to stabilize. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind scoured areas.
Aspects: All aspects.
Elevations: Alpine.
Likelihood: Likely
Expected Size: 1 - 1