Avalanche Forecast
Regions: Cascades - North West.
A consolidating and stabilizing trend should begin by Friday. But recent wind slab, storm slab, loose dry snow and tree wells will all still be key features to avoid on Thursday.
Detailed Forecast
An upper trough and cool air mass will sink to the south of the Northwest on Friday. Alpine winds should decrease and become northwest with light snow showers along the west slopes ending Friday morning. Some cloud breaks may be seen along the west slopes Friday afternoon. Fairer weather will be seen along the east slopes.
This weather should not build new snow pack layers and a gradual consolidating and stabilizing trend should begin by Friday. Cool temperatures may somewhat slow the stabilizing but the avalanche danger should be less than the previous couple days.
Recent wind slab will be most likely to linger on north to east slopes in the above and near tree line. Wind and storm slab avalanches should remain within recent storm layers but could still move fast. Test for inverted strong over weak storm snow and give cornices a wide margin.
Beware of loose dry avalanches in steep non-wind affected terrain that could have unintended consequences such as knocking you off your feet and into a terrain trap.
Remember to discuss plans with your partners or steer clear of high consequence terrain until there is more information and we know more about what is going on out there.
The recent unconsolidated storm snow is very deep in many places with possible very large tree wells. There as a snow immersion fatality in a tree well in bounds at Snoqualmie last Saturday so always travel with a partner.
Snowpack Discussion
We have had nearly a week of heavy snow and cool temperatures in the Olympics and Cascades. Sites near and west of the crest have had 5-9 FEET of snowfall during this time!
Recent pro back country or pro patrol observations indicate extensive avalanches but confined to recent storm snow.
In the Crystal backcountry on Tuesday NWAC pro observer Dallas Glass found some snow pack whumping and numerous triggered storm slab and some loose dry releases. The storm slab was releasing at about 25 and 45 cm where there were likely storm layers. The greatest wind loading and cornice formation was seen on east facing terrain near ridges.Â
Crystal backcountry near Bullion Basin, a shallow 10" skier triggered soft slab on a southwest aspect at 5800 feet. Released near noon Tuesday, December 22. Photo: NWAC pro observer Dallas Glass.
The Alpental pro patrol on Wednesday reported widespread large 12-14 inch storm slabs from explosives and ski cuts.
NWAC pro observer Lee Lazzara was in the Canyon Creek area near Mt Baker on Wednesday in the 2000-5400 foot range and found a right side up upper snow pack but with new snow layers also building quickly and a weaker storm layer at 20 cm. He noted numerous small natural and triggered storm slab and loose dry avalanches mainly on west to north to east facing slopes.
The Baker pro patrol on found fairly extensive 6-8 inch storm slab on Thursday morning. A skier out of bounds on a northwest slope at 4500 feet also triggered a 6-8 inch storm slab and was buried except for a glove showing and was luckily dug out by his friends.
NWAC pro observer Dallas Glass was at East Peak near Crystal Mountain on Thursday and reports one natural 12 inch storm slab on an east slope at 5800 feet along with several loose dry avalanches. A storm layer at 25-35 cm did not seem overly reactive. He kicked a couple cornices onto test slopes without results.
Avalanche 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: Likely
Expected Size: 1 - 1
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: Possible
Expected Size: 1 - 1
Loose Dry
Release of dry unconsolidated snow. These avalanches typically occur within layers of soft snow near the surface of the snowpack. Loose Dry avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs. Loose Dry avalanches can trigger slab avalanches that break into deeper snow layers.
Loose Dry avalanches are usually relatively harmless to people. They can be hazardous if you are caught and carried into or over a terrain trap (e.g. gully, rocks, dense timber, cliff, crevasse) or down a long slope. Avoid traveling in or above terrain traps when Loose Dry avalanches are likely.
Loose Dry avalanche with the characteristic point initiation and fan shape.
Loose dry avalanches exist throughout the terrain, release at or below the trigger point, and can run in densely-treed areas. Avoid very steep slopes and terrain traps such as cliffs, gullies, or tree wells.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 1 - 1