Avalanche Forecast
Regions: Stevens Pass.
There have not been many folks out lately due to the storms so there is some uncertainty regarding avalanche conditions.
Detailed Forecast
Northwest flow will help carry a weak low pressure system northwest to southeast across the Olympics and Cascades on Saturday. Near and west of the crest this should mainly cause west northwest winds with some light snow in the morning, becoming light to occasional moderate in the afternoon, with cool temperatures. New shallow wind slab seems possible on lee slopes mainly at higher elevations. New storm slab would be be found on sheltered slopes but should be shallow and unlikely.
Layers from the past 11 days should continue to stabilize. Possible older deeper wind slab may linger on previous lee slopes mainly at higher elevations. Watch for signs of firmer wind transported snow.
Previous older deeper storm slab on sheltered slopes should be mostly stabilized and unlikely by Saturday.
The sun is starting to get stronger as we head toward March. Watch for sun effects such as roller balls and pinwheels on solar slopes that could trigger a loose wet avalanche or a wind or storm slab layer on a steep slope.
It will have been many days since there have been many people in the back country so conditions are a bit uncertain. Careful snow pack evaluation and caution should still be essential on Saturday.
Snowpack Discussion
Recent Northwest Weather
An extended mild and dry period occurred the latter half of January generally causing a crust to form in all areas. Very cold weather followed in early February which generally produced low density snowfall and faceting near the crust.
During the past 11 days the Pacific Northwest has been pummeled almost daily by frontal systems producing periods of strong winds and heavy snowfall. The water equivalent over the past 11 days is about 9-15 inches with snowfall about 7-12 feet at NWAC weather stations near and west of the crest.
Observations for Washington Cascades near and west of the crest
Several avalanche cycles have been seen the past 11 days. West of the crest the January crust has become pretty deeply buried and there isn't any recent natural or human triggered activity down to that layer lately. Attention near and west of the crest will be focused on recent storm layers.
A cold front Tuesday evening caused heavy loading rates at gradually warming temperatures. This caused a widespread natural avalanche cycle that was seen in many areas by Wednesday morning with numerous wind and storm slab avalanches noted from the Mt Baker, Snoqualmie Pass and Crystal Mountain ski areas. Some of the avalanches were up to 3-5 feet deep!
Here is a video observation from NWAC observer Dallas Glass in the Snoqualmie Pass area Wednesday.
The last front of the 11 day storm cycle moved past on Wednesday night causing denser snow at warmer temperatures. Easy ski triggering of storm slabs on Thursday up to about 1-1.5 feet mainly on lee slopes was reported by ski areas including Mt Baker and Alpental.
West northwest winds and light snow showers are decreasing on Friday. No new natural or human triggered avalanches have been reported so far on Friday. But winds on summits and ridges are locally strong enough (for example at the top of Crystal or White Pass) to build local wind slab on lee slopes on Friday.
NWAC observer Dallas Glass was at Snoqualmie today and reports a settling stabilizing snow pack. He saw possible 30-50 cm wind slab layers on lee slopes. Storm slab was becoming unlikely except on isolated terrain features.
NWAC observer Tom Curtis was at White Pass today and reports heavy wind loading on lee slopes at 6900 feet.
The mid and base pack should still consist of mostly stable crusts and melt form layers from periods of warm weather earlier this winter.
Note that persistent slab is a concern east of the Cascade crest. Be sure to read the forecast for that area if you venture even slightly east of the crest.
Keep an eye on your riding partner in the deep snow until the new snow settles and the risk of SIS subsides.Â
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: Possible
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: Unlikely
Expected Size: 1 - 1