Avalanche Forecast
Issued: Jan 4th, 2016 10:00AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Storm Slabs.
NWAC,
Northwest Avalanche Center
New snow further accumulating on possible buried surface hoar and near surface faceted snow from around New Years will need to watched for on Tuesday. Wind slab will also need to watched for on a variety of aspects.
Summary
Detailed Forecast
A couple more weak short waves and weak bands of precipitation should move out of a large weak trough and over the Northwest on Tuesday. This will cause more periods of mostly light snow in the Olympics and Cascades on Tuesday. Several inches or more of snowfall is possible on the volcanoes. Offshore surface flow should limit snowfall in the Cascade Passes. A slight warming trend should be seen on Tuesday.
New snowfall may further load possible buried surface hoar and near surface faceted snow from around New Years. This new snow may continue to be somewhat upside down with denser snow near the surface which contributes to instability. The greatest accumulations should be from about Snoqualmie to Mt Rainier and the greatest avalanche danger will be indicated in that area.
Wind slab will need to watched for on a variety of aspects. Old wind slab may still be found on the more usual north to southeast slopes. Wind slab from over the weekend is mostly likely on west aspects. New wind slab may be starting to form in some areas again on Monday on the more usual north to southeast aspects. But new wind slab should be less of an issue in the North Cascades where winds and snowfall continue to be less.
Snowpack Discussion
Fair weather was seen the last couple days of December through the weekend. This weather caused lots of consolidation and stabilizing of the heavy snow from December. It also caused new surface hoar and near surface faceted snow in many sheltered areas.
Strong east winds were also seen New Years Eve through the weekend building wind slab on west aspects, primarily in the central and south Cascades, including the Cascade Passes.
Preliminary Granite Mountain Avalanche Fatality Information: a hiker died on Granite Mountain near Snoqualmie Pass Thursday, likely due to a wind slab avalanche on a west facing slope near treeline. The hiker was found by Search and Rescue Friday morning on top of the avalanche debris. It is not known yet whether the slab was natural or human triggered.
Rangers at Paradise reported several D1/R1 (small) skier triggered wind slab on west aspect near treeline Thursday. Two skier triggered wind slabs were also reported Thursday near Kendall peak at Snoqualmie Pass on the north and west aspects. Both were small but one ran a fair distance and took a skier for a ride.
A Paradise backcountry ranger reported two harder wind slab releases Friday on the west aspect off of Pan Face, and at least 1 wasskier triggered. In a nearby pit, the ranger determined the wind slab was about 30 cm (1 ft) deep and 1F to P hardness. He also reported a skier a small triggered wind slab release on a SW aspect in the Nisqually area.
A change Sunday night and Monday has been some snow and a warming trend. Snowfall has ranged from about 3-11 inches along the west slopes with the most from Snoqualmie to Mt Rainier.
This new snow will be upside down with denser snow near the surface and may have accumulated on surface hoar and near surface faceted snow from around New Years. The Snoqualmie DOT reported easily triggered 6-8 inch storm slab during control on Monday afternoon. The Crystal Mountain pro patrol reported widespread reactive 10 inch storm slab on Monday.
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: All aspects.
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
Valid until: Jan 5th, 2016 10:00AM
