Avalanche Forecast
Issued: Feb 10th, 2015 10:00AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Loose Wet and Wind Slabs.
NWAC,
Northwest Avalanche Center
The primary concern Wednesday east of the crest should be loose wet snow avalanches. But you will need to watch for a wider variety of conditions east of the crest than elsewhere.
Summary
Detailed Forecast
Fair weather should be seen on Wednesday with some high clouds especially over the Olympics and north Cascades. Quite a rise in freezing levels should be seen Wednesday so that means significantly warmer temperatures.
The main problem on Wednesday east of the crest should be loose wet avalanches. Watch for natural or triggered rollerballs that would initially be seen on steep solar slopes but that could spread to other slopes. Don't underestimate the power of slow moving loose wet snow avalanches which could take you some where you don't want to go such as into gullies or other terrain traps and then sets up like concrete. These conditions should extend to some extent down into the near treeline and the upper part of the below treeline.
Wind slab will linger longer east of the crest. Watch for firmer wind transported snow on previous lee slopes mainly on N-SE slopes near ridges.
As a result of the overall low snowpack, especially in the lower part of the below tree line, watch for terrain hazards such as open creeks, partially covered rocks and vegetation.
Snowpack Discussion
A series of fronts in an atmospheric river crossed the Northwest the past few days. The east slopes have seen quite a variety of weather and snow conditions. The Harts Pass Snotel and the NWAC Washington Pass weather stations total snow gages indicate about a foot of snow during this period. Other areas east of the crest have had less snow or rain.
NWAC pro-observer Tom Curtis was at Dirty Face Peak on Saturday and found small roller balls in recent snow with no recent avalanches and no signs of instability.
The North Cascade Mountain Guides were at Washington Pass on Sunday and found 30-40 cm of storm snow with touchy 6 inch storm slab above 7000 feet. They also reported lots of small loose wet avalanches at lower elevations.
The North Cascade Mountain Guides near Washington Pass on Monday also reported a size 1.5 20-30 cm deep x 25 m wide wind slab on a north slope that was remotely triggered from a shallow spot with facets near rocks. So there is definitely still some variability out there.
Regarding the potential January 15th persistent slab - NWAC pro-observers and North Cascade Guide reports last week in the northeast and central east zones have found the January 15th facet/crust layers at 35 cm-1 m below the surface with the facets starting to turn to rounded grains and not reactive or not releasing in pit tests. So it appears the January 15th facet/crust layers are strengthening and stabilizing. This problem has been removed from the central east zone forecast but retained in the northeast zone until more information becomes available there.
Problems
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
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
Valid until: Feb 11th, 2015 10:00AM
