Cooler weather with a chance of a few light showers should maintain some shallow wet snow or crust layers. Watch for unexpected wet snow deeper than boot top. The cooler weather should limit the avalanche potential Wednesday.
Summary
Detailed Forecast
Cooling with cloud cover and a chance of a few light rain showers in the north zone is expected Wednesday. The cooling should allow for firm crusts and limited surface snow to melt, causing a lower probability of wet snow avalanches.
Only very light amounts of rain, if any, are expected, mainly in the north zone, and that should not cause a significant increase in wet surface snow.
Continue to watch for 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. .
Watch for recent cornices along ridges which may become sensitive to trigger.
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.
The warmest weather of the season arrived Monday and Tuesday. Temperatures along the east slopes reached the mid 40's to 50's both Monday and Tuesday near treeline and above treeline, with cooler temperatures below treeline. This caused a significant snowpack settlement, and wet snow conditions, especially on solar aspects both Monday and Tuesday.
Recent Observations
Extensive observations in the Washington Pass area over the past few days indicated an active loose-wet avalanche cycle occurred, mainly Monday afternoon. The recent storm snow has become homogenous with the warming, destroying any storm layers from late last week.
NWAC pro-observer Tom Curtis in the Blewett Pass area Tuesday found the early January buried layers non-reactive, likely due to further strengthening and settlement following the very warm weather over the past two days. ?
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 10th, 2016 10:00AM
