Avalanche Forecast
Regions: Olympics.
Watch for areas that might receive greater than expected snowfall later Saturday or wind transport that begins to build slab layers over a new facet/crust layer near the surface. Also give recently formed cornices a wide berth and avoid travel under slopes with large overhanging cornices. Continue to choose terrain conservatively and avoid large open avalanche terrain as the concern for a deep persistent slab remains, even though it is a low frequency, unlikely outcome, the consequences are high.
Detailed Forecast
Significant cooling is expected Friday night and Saturday with mostly cloudy conditions and a few generally light snow showers expected late Saturday.  This weather should cause the previously wet surface and upper snow layer to re-freeze, forming a hard and supportable crust.  The surface or near surface crust should limit the avalanche potential, especially near and below tree line.  Any new snow received Saturday is not expected to be significant to cause a notable increase in the danger Saturday. Â
The strengthening new surface crust expected Saturday should cause generally safe avalanche conditions.  However continue to watch for unstable snow on isolated terrain features, especially near and above treeline if new snow or wind transport begins to develop new slab layers over observed weak surface facets noted above the newly formed crust.  Also watch for recently formed large cornices along ridges and give them a wide birth and safety margin.  Some of these cornices have grown large over the last 2 weeks and a cornice failure could provide a large enough load to trigger a large avalanche.Â
Snowpack Discussion
Recent Northwest Weather
An extended mild and dry period occurred the latter half of January generally forming a crust in all areas. Very cold weather followed in early February which produced light low density snowfall, near surface faceting, and faceting near and just above the crust.
Weaker frontal systems last weekend followed the frequent strong storms over the past 2 weeks.  We have finally ended the extended storm cycle as of Monday night, capping off impressive amounts of some 6-7 feet of new snow with a rain event that reached to near 7000 feet in the Hurricane Ridge area and likely other Olympic areas.Â
Temperatures Tuesday through Thursday this week have been well above freezing with plenty of sunshine.  Hurricane Ridge high temperatures reached into the 40's all 3 days. while Friday has cooled a bit but briefly hit another 40 F max along with sunny weather and gradually increasing ENE winds.  Significant snowpack settlement of some 12-15 inches has occurred, especially below treeline during this warm stretch.
Observations for Hurricane Ridge area
Recent deep snow conditions took a dramatic turn for the worse Monday in the near and below tree line zones as rain returned and fell through Monday night. The generally light to moderate rain that fell through late Monday night quickly changed the recent low density dry snow to wet snow conditions.  A NPS ranger at Hurricane Ridge Tuesday morning reported evidence of recent widespread wet snow avalanches running on most steeper slopes and a variety of aspects.  This situation likely repeated itself on Wednesday and to a lesser extent Thursday and Friday, especially during sun breaks.Â
The latest observation on Friday, Feb 28th by NWAC pro observer Tyler Reid comes from Klahhane Ridge to the east of Hurricane where plenty of wet unconsolidated snow was found on solar aspects below tree line from 4400-5600 feet.  No strong layers were seen in this area with easy pole probing to the ground.  Above 5600 feet, 3-5 cm of new snow existed over a thin crust on solar aspects with a 5 cm supportable crust on shaded slopes.  Some small surface hoar growth was noted in places.  There was much evidence of the recent rain an warming with runnels found on all aspects with many small size 1 loose wet slides. For the latest conditions report from that area see this video from Friday.
The late January crust layer and associated weak layers of early February are now deeply buried by all the new storm snow and were producing areas of collapsing and large whumpfing last weekend prior to the warm up and rain.  These conditions were found in a NE meadow below treeline by a frequent back country traveler in the Hurricane Ridge area last weekend. The same skier had pictures of some very large cornice collapses.  While triggering a slide on this layer has become much less likely, we are still urging more conservative travel plans as the consequences of a slide on that layer could be devastating.
The mid and base pack around the Hurricane Ridge area may still consist of some stable crusts and melt form layers from periods of warm weather earlier this winter.  However the the report from Friday on solar aspects below treeline indicating full depth unconsolidated wet snow indicates not all areas are maintaining deeper crust layers.Â
Avalanche Problems
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: Alpine, Treeline.
Likelihood: Unlikely
Expected Size: 1 - 1
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, North West.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 2