Avalanche Forecast
Regions: Stevens Pass.
A mixed bag of conditions is possible in the Cascades on Sunday. Recent or older wind slab should be the main avalanche problem along the west slopes. Loose wet avalanche conditions may also linger where warm temperatures are still seen on Sunday.
Detailed Forecast
A weakening front will move over the upper ridge and cause increasing alpine winds on Sunday. It should still be mild or warm along the west slopes and at higher elevations through the morning hours. Then light rain or snow should spread to the Olympics and northwest Cascades Sunday afternoon with a cooling trend beginning in all areas.
The main avalanche problem in the west Cascades should be recent or older wind slab mainly on northwest to southeast slopes near and above treeline. But watch for firm wind transported snow on all aspects in the upper terrain bands. Note the skier triggered wind slab avalanches that were reported on Mt Herman on Saturday.
A secondary avalanche problem should be possible lingering loose wet avalanche conditions where warm temperatures are still seen on Sunday. Increasing winds may help keep surface snow firmer and limit loose wet avalanche conditions above treeline. Watch for pinwheels, natural releases of any size and wet surface snow deeper than a few inches.
Snowpack Discussion
Weather and Snowpack
An arctic air mass settled over the Northwest with fair, very cold weather the second week of January.
An atmospheric river arrived over the Northwest Tuesday 1/17 with highly variable weather seen throughout the Cascades during this event. Heavy rain was seen up to about 6000 feet or higher in the North Cascades and up to about 7000 feet or higher in the south with snow at higher elevations. Three day precipitation totals through Thursday 1/19 were roughly 8 inches at Mt Baker, 5 inches at Crystal and 1-2 inches at the Passes. Sleet and freezing rain Tuesday 1/17 at the Passes changed to snow at higher elevations at Stevens and Snoqualmie on Wednesday 1/18.  At Stevens and Snoqualmie Pass the freezing rain crust is about 1 inch thick.
The most recent storm cycle from Thursday 1/19 through Sunday 1/22, deposited 1-2 feet of snow along the west slopes of the Cascades with the greatest totals seen at Mt. Baker. Strong S-SE winds also built unstable wind slabs on lee slopes primarily in the central and south Washington Cascades.
Clouds and cool weather with little to no new snow accumulation occurred Tuesday and Wednesday.
A large upper ridge and warm air mass built over the Northwest Thursday to Saturday. By Saturday temperatures have reached the 40's at Hurricane and at higher elevations especially along the west slopes. Cooler temperatures are seen Saturday at Stevens and Snoqualmie and at lower elevations along the east slopes.
Recent Observations
North
NWAC pro-oberserver Lee Lazzara was out in the Mt Baker area on Grouse Ridge Thursday. In this area, there were less recent wind effects with the last storm cycle and wind slabs were not encountered in terrain up to about 5800 feet. The rain crust from 1/17 was generally buried about 1 foot and showed good bonding to the settled storm snow. No avalanches were seen or triggered, with nice settled powder conditions still providing good quality skiing. Lee noted widespread small surface hoar formed over the past few days and if buried by a light snowfall in showers may become a layer to watch out for with future loading.  Glide cracks were also seen on some slopes in this area below treeline.
AÂ new observation for Saturday came to the NWAC Saturday night with skiers reporting 3 triggered wind slab avalanches of about 2 feet on N-E slopes on Mt Herman near Mt Baker with a burial to the waist of 1 person. No other details are currently available.
Central
Dallas Glass was back in the Snoqualmie Zone Thursday in the Denny Mountain area. Older wind slabs responsible for many triggered avalanches early this week, had now stabilized significantly and were no longer deemed an avalanche problem in this terrain. This observation is supported by the numerous aggressively skied terrain features throughout the Alpental Valley over the past few days with little to no avalanche activity. In snowpit tests, Dallas did find well formed facets above the 1/17 crust and this layer produced reactive snowpit tests, especially on solar aspects. These preliminary observations are limited in understanding the distribution or sensitivity of this layer, so more investigation is planned.
A report on Turns All Year for the Snoqualmie Pass area indicated some good conditions still to be found on some north slopes.
South
The Crystal pro-patrol reported extremely sensitive new wind slabs on NW aspects Sunday morning 1/22. About 4-6 inches of new storm snow were transported by very strong S-SE winds overnight and early Sunday morning. This built very sensitive wind slabs on lee slopes by early Sunday. Wind slabs, mostly in the 6-8 inch range, released sympathetically and were running long distances. Shooting cracks were extending over 100 feet from skis.
By Monday and Tuesday the Crystal pro-patrol reported that previous reactive wind deposited snow had bonded and greatly stabilized with no new avalanches.
On Friday the Crystal pro-patrol had not observed any avalanche activity for several days. But sun breaks were greatly affecting snow on solar aspects.
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, North West.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 1
Loose Wet
Release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.
Several loose wet avalanches, and lots of pinwheels and roller balls.
Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.
Aspects: South East, South, South West.
Elevations: All elevations.
Likelihood: Unlikely
Expected Size: 1 - 1