Avalanche Forecast
Issued: Nov 26th, 2016 11:03AM
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
Watch for previously formed wind slab layers on Sunday especially in the northeast to central east zones. Be prepared to ratchet back your plans if conditions get stormy again before the end of the daylight hours on Sunday.
Summary
Detailed Forecast
Forecast for the Cascade East Slopes
A relative short break in the weather should be seen much of Sunday so conditions shouldn't change too much on Sunday.
There is still a lot of variation in snow cover depending on elevation since it is early in the year. Expect winter conditions at the higher elevations and too little snow for avalanches at the low elevations.
While this forecast is for a moderate avalanche danger mainly above tree line the report above sure indicates you better be watching for potential wind slab. The potential for triggering does not seem great but such an avalanche can have deadly consequences. Watch for signs of firmer wind transported snow.
Note that the next system is due to begin to arrive late in the day on Sunday. Be prepared to ratchet back your plans if conditions get stormy again before the end of the daylight hours on Sunday.
Snowpack Discussion
Weather Discussion for the Cascade East Slopes
There has been a lot of variation depending on location in weather and snow conditions in the Olympics and Cascades the past couple days.
Moderate snow has fallen the past few days in the northeast and north part of the central east zones. But direct measurements have been somewhat lacking as the weather station gremlins have been having their fun the past few days at the NWAC and NRCS Snotels.
Less snow has fallen lately in the southeast zone.
Decreasing south winds and a cooling trend should be seen on Saturday as a weakening front shifts to the east. Some light amounts of snow seem likely along the east slopes.
Recent Reports for the Cascade East Slopes
There are few recent reports for the Cascade East Slopes. However on Friday a skier triggered a deep wind slab on a 40 degree northwest slope at about 7500 feet on Slate Peak near Harts Pass. The crown varied from about 2 to 7 feet and ran about 2-300 vertical feet with car sized chunks of debris. Fortunately the skier was not caught. He noted that windward slopes across the valley were scoured indicating recent wind transport.
There are currently no indications of any persistent weak layers along the Cascade east slopes.
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, 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
Valid until: Nov 27th, 2016 11:03AM
