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 wind and storm slab layers on Sunday that may be left over from Saturday especially in the Mt Baker area. 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 West Slopes
A relative short break in the weather should be seen much of Sunday with some light snow showers so conditions shouldn't change too much on Sunday.
This forecast will err on the side of caution and emphasize the avalanche danger in the Mt Baker area 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.
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 West 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.
Snow has been heavy in the Mt Baker area where the NWAC station at the ski area has had 62 inches of snow in the past 4 days ending Saturday morning with a warming trend which spells avalanches there.
Snow amounts have been less elsewhere along the west slopes with about 7-29 inches in the past 4 days with the most at Paradise and with little for the 24 hours ending Saturday morning.
Decreasing south winds and a cooling trend should be seen on Saturday as a weakening front shifts to the east. About 5-10 more inches of snow is likely on Saturday in the Mt Baker area and perhaps about 2-5 more inches should be seen elsewhere.
Recent Reports for the Cascade West Slopes
The Mt Baker pro patrol reported local natural and widespread sympathetic and remote ski triggered wind or storm slab avalanches on Saturday morning. These were mainly on north to northwest slopes in the 4500-5000 foot range since this is the avalanche terrain of the ski area.
Some reports for Friday via the NWAC Observations tab for the Crystal Mountain area indicate some recent upside down surface layers with some clean shears in pit tests and some ski triggered wind slab avalanches up to R3/D3 in size.
A skier was caught but not injured in triggered storm slab avalanche on Mazama Ridge near Paradise on a 35 degree southeast facing slope at about 6000 feet on Friday. The slab was about 10 cm x 30 m wide and the debris remained soft and fortunately there was a safe run out without obstacles such as trees or a terrain trap.
Mazama Ridge avalanche from Friday. Photo courtesy of Radka Chapin.
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
