Avalanche Forecast
Regions: Olympics.
Wet snow conditions will persist, maintaining the potential for glide avalanches on steep unsupported terrain features that may not have released during recent heavy rains. Much of the below treeline elevation band does not have enough snow cover to support an avalanche hazard. Isolated pockets of wind slab may exist near and above treeline on northerly aspects.
Detailed Forecast
Rain is expected Saturday night through Sunday morning at Hurricane Ridge with strong winds. A cold front should push through in the early afternoon and snow levels will drop to 3500-4000 feet by 4 pm. Â
Wet snow conditions will persist, maintaining the potential for glide avalanches on steep unsupported terrain features that may not have released during recent heavy rains. Much of the below treeline elevation band does not have enough snow cover to support an avalanche hazard. Isolated pockets of wind slab may exist near and above treeline on northerly aspects.Â
Watch for the numerous travel hazards such as open creeks, barely buried rocks and trees, and glide cracks, creating poor and challenging travel conditions, especially below treeline.Â
Remember that closed ski areas without avalanche mitigation are equivalent to backcountry terrain! Â
Snowpack Discussion
New resources within your Avalanche Forecast this season!Â
The Mountain Weather tab will take you to the most recently issued Mountain Weather Forecast. The Observations & Weather Data tab will allow an easy view of the various weather station graphs within your zone of interest and provide easy access to the most recent avalanche and snowpack observations.Â
The great start of winter 2017/18 in the PNW has taken a recent hit as warm wet weather arrived Tuesday morning and lasted through Thanksgiving. The Hurricane Ridge area received over 5 inches of rain since Tuesday morning, reaching well above the terrain in that area. The warming and rain initially triggered numerous wet snow and glide avalanches earlier this week, mostly reported on Tuesday and Wednesday in the Washington Cascades. Â
Rain has now melted significant snow with average snow depths decreasing about 50% since Monday! Hurricane Ridge decreased from a snowdepth of about 4 Monday to about 2 feet as of Friday. This has allowed much of the previously well snow covered terrain to open with many creeks and snow bridges re-appearing, especially near and below treeline.Â
The wet or saturated snowpack continues to drain and as of Friday afternoon is beginning to solidify and begin slowly re-freezing.
Cooling since Thursday with additional, mostly light precipitation, has begun to add some new snow above the old wet snowpack. The Hurricane Ridge area only received about 2 inches of new snow as of Friday afternoon.
Observations
NWAC pro-observer Matt Schonwald was out in the Hurricane Ridge area on Saturday. Matt found pockets on wind slab up to 15 cm (6") thick on north aspects of Mt. Angeles near 5000 feet. The wind slab was stubborn to trigger and did not propagate.  A few glide cracks were visible in the Hurricane Ridge area, but only large slide was observed from the recent rain events off the south side of Mt. Angeles. Windward slopes above treeline were largely stripped of snow.Â
Avalanche Problems
Glide Cracks
A release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. They are often preceded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.
Predicting the release of Glide avalanches is very challenging. Because Glide avalanches only occur on very specific slopes, safe travel relies on identifying and avoiding those slopes. Glide cracks are a significant indicator, as are recent Glide avalanches.
This Glide avalanche broke to the ground on a smooth, grassy slope. From all the mud on the bed surface, water pooling at the base of the snowpack likely caused the failure.
Glide avalanches occur when water lubricates the interface between the snowpack and the ground. These avalanches are difficult to predict and best managed by avoiding terrain below glide cracks.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Unlikely
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: North, North East, East, South East, North West.
Elevations: Alpine, Treeline.
Likelihood: Unlikely
Expected Size: 1 - 1