Avalanche Forecast
Issued: Jan 14th, 2016 3:19PM
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
Mostly light amounts of new snow Friday are not expected to cause a great change in snow conditions. Adjust your plans if you are out and find more than a few inches of new snow on Friday.
Summary
Detailed Forecast
A system will move mainly across Oregon and north California on Thursday night. This system should spread some moderate snow as far north as Mt Hood on Thursday night and Friday morning with way less in the Olympics and Washington Cascades.
Some snow showers should drift north mainly over western Washington on Friday. This should bring mostly light amounts of new snow in the Olympics and Washington Cascades and are not expected to cause a great change in snow conditions along the east slopes.
Wind slab from January 12-14th should be most likely on ridges and on north to southeast slopes near and above treeline. Watch for signs of hollow snow and firmer wind transported snow.
Storm slab where it might still exist from January 12-14th could linger on more varied aspects but should be becoming unlikely and should be stabilizing.
New wind or storm slab layers would be possible if there is more snow than expected on Friday. Be prepared to adjust your plans if you are out and find more than a few inches of new snow on Friday.
Snowpack Discussion
Fair weather over the New Year caused extensive surface hoar and near surface faceted snow. This was buried by about 4-13 inches of snowfall from about January 3-6th along the east slopes. Observations near Blewett Pass, Holden, and for Red Mountain near Salmon La Sac in early January helped confirm the extent and initial sensitivity of this layer.
Another fair weather period was seen from about January 7-11th. Surface hoar formed in many areas during this period.
The latest period of snowfall has been from about January 12-14th with about 4-16 inches along the east slopes.
We have a couple reports via the North Cascades Guides from Tuesday and Wednesday.
At Washington Pass on Tuesday some small wind slab with increasing sensitivity was seen near ridges with minor cracking and minor propagation.
On Delancey Ridge on Wednesday easily triggered wind slab of about 20-25 cm was seen on north and south slopes at about 6000 feet which was releasing on a crust buried on January 11th. A 20-25 cm storm slab was also remotely triggered on a south slope at about 5000 feet which released either on the crust buried on January 11th or on the buried surface hoar from January 3rd. Natural avalanches were also heard in the 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, South East.
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: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Jan 15th, 2016 3:19PM
