Avalanche Forecast
Issued: Feb 7th, 2016 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
A warm and sunny day with freezing levels pushing above 12,000 feet Monday will point the avalanche danger toward loose wet avalanches. Steeper solar slopes near and above treeline should be the most likely places for natural or skier triggered loose wet avalanches. Slabs overlying surface hoar buried on February 3rd in the Mission Ridge area may still be sensitive, so conservative decision making will be essential until you know the extent of new persistent weak layers in your area.
Summary
Detailed Forecast
A warm and sunny day with lighter alpine winds should be seen on Monday. As freezing levels push above 12,000 feet, the avalanche danger will focus on loose wet avalanches. Steeper solar slopes near and above treeline should be the most likely places for natural or skier triggered loose wet avalanches. Solar slopes involve more than just due south aspects as we head further into February.
The hazard should be locally lower below treeline in areas affected by cool easterly flow or in areas that form a stout crust Sunday night.
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.
Lingering wind slab on lee slopes near and above treeline should be stubborn to trigger, but still possible in isolated locations on Monday.
Snowpack Discussion
Weather and Snowpack
Two fair weather periods in January allowed surface hoar and near surface faceting to occur. These persistent weak layers were buried intact on Jan 3rd and 11th, but are no longer considered a persistent slab threat after several warm and wet systems tested this layer and it has been unreactive where it can still be identified in snowpit tests.
A wet and warm front Jan 27-28th formed a crust along the east slopes. A series of frontal systems have deposited snow on top of this crust, with 30-40 cm of settled storm snow on top of the crust reported in the Washington Pass area.
The last frontal system that blew through Friday night brought light new snow accumulations but westerly transport winds were strong.
Sunny skies were seen over the southern half of the east slopes Sunday, while sunbreaks made an appearance over the northeast Cascades. Freezing levels rose on Sunday, but were muted by moderate alpine winds and in areas with cloud cover.
Recent Observations
NWAC pro-observer Tom Curtis observed healthy surface hoar growth in the Blewett Pass area on all aspects Monday 2/1 and in the Icicle Creek drainage near and above 4500 ft Tuesday 2/2. Increased cloud cover in the Washington Pass zone likely limited surface hoar development in that area.
The North Cascade Mountain Guides and Heli operation reported good snow conditions through Friday with little recent avalanche activity.
The likely most significant observation comes from an avalanche class touring in the 4000-7000 foot range near Mission Ridge Friday. The group was remotely triggering small to large 20-45 cm wind slab on lee N-SE slopes due to the surface hoar layer buried on February 3rd. The layer was also found at about 10 cm in non-wind affected areas.
Mission Ridge pro-patrol did not have any new information on this layer Sunday, but it is likely becoming less reactive with the recent warm weather.
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: South East, South, South West, West.
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 8th, 2016 10:00AM
