The avalanche danger is expected to be limited for most of daylight hours on Thursday. Change your plans if the next system arrives sooner than expected and you see significant layers of new snow starting to build at higher elevations or significant wet snow deeper than boot top at lower elevations.
Summary
Detailed Forecast
A relative break between systems with little change in snow levels and temperatures should be seen most of the daylight hours on Thursday.
Continue to watch for loose wet avalanche potential above terrain traps such as above cliffs, near gullies or where avalanche debris would deeply accumulate. These are the types of places that even small wet avalanches can have serious unintended consequences.
Avoid cornices along ridges and slopes below cornices since cornices may still be weaker due to the warm weather.
Rain and snow from a warm front should start to move into the Northwest Thursday late afternoon. Be prepared to change your plans if this system arrives sooner than expected and you see significant layers of new snow starting to build at higher elevations or significant wet snow deeper than boot top at lower elevations.
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 recent snowpit tests.
A large upper ridge and warm air mass aloft has been over the US west coast the past 3 days. Temperatures at NWAC stations along the east slopes reached the 40 to 50 degree F range near and above treeline with cooler temperatures in the below treeline which is the warmest weather so far this season. The very warm temperatures and solar effects caused loose wet avalanches, consolidation and night-to-morning surface crusts. This will have further stabilized the lower and mid snow pack and turned recent storm snow into moist to wet snow especially on solar aspects.
An initial weak front is moving over the Northwest today. Areas at higher elevations may see a little light rain with a lowering of high snow levels. This should not greatly change snow conditions.
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.
NWAC pro-observer Jeff Ward was in the Washington Pass area in the 6-7600 foot range on Tuesday and saw several size 1 natural loose wet avalanches on steep solar slopes.
NWAC pro-observer Tom Curtis in the Blewett Pass area in the 4-5900 foot range Tuesday and also saw several small to large wet loose avalanches on solar slopes near and above tree line.
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.
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.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Feb 11th, 2016 10:00AM
