Avalanche Forecast
Issued: Feb 6th, 2016 10:23AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Loose Wet.
NWAC,
Northwest Avalanche Center
Lingering wind slab on lee slopes near and above treeline may be tougher to trigger, but still possible on Sunday. Wet loose avalanche potential will vary considerably through elevation bands and location, largely impacted by how the weather forecast plays out. Moderate avalanche danger means heightened avalanche conditions (hazard) on specific terrain features, so match your terrain selection to the avalanche problems.
Summary
Detailed Forecast
A warm front lifting north across the area should bring light rain and clouds to the north Cascades and filtered sunshine to the south Cascades on Sunday. A warming trend will begin Sunday, but will likely be tempered by moderate winds above treeline, light but cool easterly flow through the Passes and extensive cloud cover for the northern 2/3rds of the Cascades. However, there is a decent amount of uncertainty for Sunday's forecast.
Lingering wind slab on lee slopes in the near and above treeline elevation bands may be tougher to trigger, but still possible Sunday. Watch for signs of snowpack cracking and firmer wind transported snow on lee slopes.
Wet loose avalanche potential will vary considerably through elevation bands and location, largely impacted by how the weather forecast plays out Sunday. Light rain in the north and sunbreaks in the south will encourage natural wet loose activity on steeper slopes predominately near and below treeline. Be aware of loose wet avalanche potential above terrain traps (like above cliffs or near gullies), where even small wet avalanches can become powerful and have unintended consequences.
Snowpack Discussion
Weather and Snowpack
The last heavy rain event January 27-28th further stabilized the mid and lower snowpack and formed a strong rain crust that is being loaded by recent storms. Subsequent sun crusts and surface hoar formed early last week have not played a role in recent avalanches.
A cold front and then a warm front crossed the Northwest on Wednesday and Thursday. NWAC stations along the west slopes for the 2 days ending Friday morning had about 9-14 inches of snowfall with 18 inches at Mt Baker and 21 inches at Paradise.
A quick but powerful front moved through Friday night. About 4-10" of snow was recorded for NWAC west slope stations through mid-day Saturday, however strong SW to W winds caused significant transport even down into the below treeline band. Rain moved up to 4000-4500' in the south Washington Cascades on Friday evening before snow levels lowered.
Recent Observations
NWAC pro-observer Lee Lazzara was near Mt Baker on Thursday mainly near and below treeline and found 65-90 cm of storm snow on the crust buried January 29th. Lee and several other avalanche professionals along the west slopes reported sensitive storm layers Thursday, with patrols seeing some small storm slabs and wet loose activity.
On Saturday, Alpental pro-patrol reported small yet extensive wind slab on the upper mountain averaging 6-10". Stevens and Baker patrols saw less results despite significant wind transport. In general the new snow came in right side up and bonded well to the old snow surface.
There was a serious accident that occurred in the Crystal backcountry on Saturday. Two skiers descending East Peak crossed from a windward slope to a lee slope above Ted's Buttress a few hundred feet below the peak. One triggered a wind slab upslope of his position. Both were caught, at least partially buried by the slide and sustained injuries. One was able to self-extricate and then eventually freed his partner after considerable digging. Initial estimates are the slab averaged 30-50 cm, max 1 m in depth, and about 100 m in width. The slope in question would have been loaded by SW winds. Preliminary details were provided by Crystal Mt Pro-patrol and are subject to change as more information becomes available.
Problems
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.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Loose Wet
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. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. 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.
Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.
Several loose wet avalanches, and lots of pinwheels and roller balls.
Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Feb 7th, 2016 10:23AM
