Cooler weather with a few light showers should maintain some shallow wet snow or crust layers. Watch for unexpected wet snow deeper than boot top. The cooler weather should limit the avalanche potential Wednesday.
Summary
Detailed Forecast
Cooling with cloud cover and a few light rain showers are expected Wednesday. The cooling should allow for firm crusts and limited surface snow to melt, causing a lower probability of wet snow avalanches.
Only very light amounts of rain are expected, mainly in the Mt Baker area, and that should not cause a significant increase in wet surface snow.
Continue to watch for loose wet avalanche potential above terrain traps (like above cliffs or near gullies), where even small wet avalanches can become powerful and have unintended consequences. .
Watch for recent cornices along ridges which may become sensitive to trigger.
Snowpack Discussion
Weather and Snowpack
The last heavy rain event January 27-28th further stabilized the mid and lower snowpack and formed a strong rain crust. Subsequent sun crusts and surface hoar formed early last week have not played a role in recent avalanches outside of the Crystal backcountry.
After a moderate snowfall Wednesday/Thursday last week, a quick but powerful front moved through Friday night. About 4-10" of snow was recorded for NWAC west slope stations through mid-day Saturday, however strong SW to W winds caused significant transport even down into the below treeline band. Rain moved up to 4000-4500' in the south Washington Cascades on Friday evening before snow levels lowered.
Temperatures over most west slope stations have been in the 50's for over 24 hours straight with max temperatures reaching into the 60's both Monday and Tuesday afternoon! The past two days have seen the warmest weather of the season. The very warm temperatures and solar radiation have caused wet snow conditions with crusts forming nights and mornings with the overall snowpack settlement of about 5-10 inches since Sunday morning.
This extended warm weather has turned the recent storm snow to a rather homogenous layer of moist to wet snow in most areas.
Recent Observations
On Sunday, cloud cover and cool east flow at the Passes muted the warm up and loose wet activity from Snoqualmie Pass to Mt. Baker. Sunnier skies and warmer temps caused a small loose wet cycle in the Crystal area by late morning.
On Monday and again Tuesday, sunshine and temperatures into the mid 50's to lower 60's have likely settled recent wind slabs and shifted the main avalanche concern to wet snow avalanches. Reports from several west slope sites indicated the most active cycle of loose-wet avalanches occurred Monday, with less activity seen Tuesday. Light to moderate winds helped to maintain firmer surface snow on exposed slopes, however, plenty of moist to wet surface snow made travel, well, less than desirable.
Accident details: There was a serious accident that occurred in the Crystal backcountry on Saturday. Two skiers descending East Peak crossed from a windward slope to a lee slope above Ted's Buttress a few hundred feet below the peak (5900 ft). One triggered a wind slab on a shallow portion of the slab (40 cm) that broke well upslope of his position. Both were caught, at least partially buried by the slide and sustained injuries. One was able to self-extricate and then eventually freed his partner after considerable digging. Initial estimates are the slab averaged 40-50 cm, max 130 cm in depth, and about 100 m in width. The slope in question would have been loaded by W-SW winds. A fracture line profile performed by Crystal Mt pro-patroller Peter Dale on Sunday identified the slab released on buried surface hoar from early last week on top of the 1/28 rain crust. The slide ran over 500 ft, with the skiers carried about less than 200 vertical feet.
Problems
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, West.
Elevations: All elevations.
Likelihood
Expected Size
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind lips of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
Cornices can never be trusted and avoiding them is necessary for safe backcountry travel. Stay well back from ridgeline areas with cornices. They often overhang the ridge edge can be triggered remotely. Avoid areas underneath cornices. Even small Cornice Fall can trigger a larger avalanche and large Cornice Fall can easily crush a human. Periods of significant temperature warm-up are times to be particularly aware.
A corniced ridgeline. A large cornice has formed at the top of the ridge. A smaller cornice has formed to the left of the trees from crossloading.
Cornices are easy to identify and are confined to lee and cross-loaded ridges, sub-ridges, and sharp convexities. They are easiest to trigger during periods of rapid growth (new snow and wind), rapid warming, and during rain-on-snow events. Cornices often catch people by surprise when they break farther back onto flatter areas than expected.
Aspects: North, North East, East, South East.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Feb 10th, 2016 10:00AM
