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
Another warm and sunny day with light winds is expected again Tuesday. Temperatures pushed into the mid 50's Monday afternoon and it may be a few degrees cooler Tuesday. The avalanche danger will again focus on loose wet avalanches. Steeper solar slopes 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.
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 may be possible in isolated locations on Tuesday.
Watch for recent cornices along ridges which may become sensitive to trigger or release naturally during the warm weather.
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. There have been some local tests in the Blewett Pass area this weekend that did identify the buried January layers and showed reactive in stability tests. This layer may still a possible concern but more isolated at this point.
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.
The warmest weather of the season is upon us Monday, Feb. 8th. Temperatures along the east slopes reached the mid 40's Sunday and have warmed further Monday, ranging from the mid 40's to the low to mid-50's! This is causing significant snowpack settlement, and wet snow conditions, especially on solar aspects by Monday afternoon.
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.
A significant recent 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.
The North Cascade Mountain Guides and Heli operation reported good snow conditions Sunday morning, that became very poor by afternoon with the rising temperatures. Little recent avalanche activity was seen, except for a few soft slab releases below steep cliffs that may have been loaded by sluffing from above.
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
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind lips of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
Cornices can never be trusted and avoiding them is necessary for safe backcountry travel. Stay well back from ridgeline areas with cornices. They often overhang the ridge edge can be triggered remotely. Avoid areas underneath cornices. Even small Cornice Fall can trigger a larger avalanche and large Cornice Fall can easily crush a human. Periods of significant temperature warm-up are times to be particularly aware.
A corniced ridgeline. A large cornice has formed at the top of the ridge. A smaller cornice has formed to the left of the trees from crossloading.
Cornices are easy to identify and are confined to lee and cross-loaded ridges, sub-ridges, and sharp convexities. They are easiest to trigger during periods of rapid growth (new snow and wind), rapid warming, and during rain-on-snow events. Cornices often catch people by surprise when they break farther back onto flatter areas than expected.
Aspects: North, North East, East, South East, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Feb 9th, 2016 10:00AM
