Avalanche Forecast
Issued: Jan 12th, 2016 10:00AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs, Storm Slabs and Loose Wet.
NWAC,
Northwest Avalanche Center
The avalanche danger should remain elevated in the morning with a slow decreasing trend through the afternoon as storm instabilities begin to stabilize. Cautious route-finding and terrain selection will be essential on Wednesday to stay safe and avoid storm related avalanche problems.
Summary
Detailed Forecast
Light to moderate snowfall Tuesday night should taper down Wednesday. Moderate precipitation should hang on longest for the central and southeast Washington Cascades through the morning hours. A warming trend should take place Wednesday morning as warmer Pacific air mixes along the east slopes leading to a modest bump in snow levels.
The avalanche danger should be elevated in the morning with a slow decreasing trend through the afternoon as storm instabilities begin to stabilize. Cautious route-finding and terrain selection will be essential on Wednesday to avoid storm related avalanche problems.
Stay off steeper slopes and allow storm instabilities time to settle. Look for wind slab on a variety of aspects near and above treeline due to shifting winds. Watch for signs of firmer wind transported snow that can indicate wind slab layers near and below ridges. Storm slabs will be more likely to trigger in the Mission Ridge area on sheltered aspects above 5000 feet if recently formed surface hoar was buried intact.
Loose wet avalanches are likely Wednesday below 3500-4500 feet on steeper slopes that see a warming trend and/or light rain.
Snowpack Discussion
Fair weather that lasted about a week over the New Year caused extensive surface hoar and near surface faceted snow that was later buried by light snowfall Jan 3rd-4th. Observations forBlewett Pass, Holden, and for Red Mountain near Salmon La Sac in early January helped confirm the extent and initial sensitively of this layer. However, these layers and a buried surface hoar layer 60 cm down in the Blewett Pass area from mid-Dec have likely gained significant strength due to the mild temperatures over the last week.
The North Cascade Mountain Guides were at Washington Pass last Friday and found that the recent storm snow was surprisingly well bonded to the previous snow in spite of the recently buried surface hoar and faceted snow at the Jan 3rd interface. Tests and ski cuts gave no results due to little slab structure of the recent snow.
Avalanche professionals in the Mission Ridge area Sunday and an observation via the NWAC page Monday reported widespread surface hoar growth on northerly aspects above 5000 feet. Light snowfall Tuesday may have buried this weak layer on sheltered non-solar aspects above 5000 feet in the Mission Ridge area.
Problems
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, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Storm Slabs
Release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. Storm-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.
You can reduce your risk from Storm Slabs by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.
Storm slabs usually stabilize within a few days, and release at or below the trigger point. They exist throughout the terrain, and can be avoided by waiting for the storm snow to stabilize.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
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.
Elevations: Below Treeline.
Likelihood
Expected Size
Valid until: Jan 13th, 2016 10:00AM
