Avalanche Forecast
Regions: Olympics.
Loose wet slides may entrain deeper layers, becoming powerful and with the potential to carry you into trees. Avoid solar aspects during peak warming hours. On north-facing terrain, watch for isolated wind slab pockets and test for storm slab to make sure it has stabilized as expected.
Detailed Forecast
Expect continued sunny weather and further warming tomorrow.
The warming is preventing the refreezing of south-facing snow from the Thanksgiving event. As the south-facing terrain heats under solar warming tomorrow, it is expected to entrain progressively deeper snow layers and may produce some avalanches with significant destructive potential. Avoid slopes at all elevations that are being directly impacted by the sun.
Recent storm and wind slab layers in dry snow on north-facing aspects will continue to stabilize in the Hurricane Ridge area. The storm slab found to be reactive in compression today is not expected to be reactive tomorrow as the healing process continues under warm temperatures.
Relatively new, small wind slabs have been forming on all aspects north of the ridge divide and will continue to form overnight. These wind slabs are expected to be stubborn or difficult to trigger, small, and shallow. Watch for small areas of firmer, wind-transported snow on isolated, lee terrain features.
Early season terrain hazards still exist, such as poorly covered rocks, vegetation and creeks, particularly at lower elevations.
Snowpack Discussion
Warm, very wet weather before Thanksgiving caused wet snow and glide avalanches as well as snowpack consolidation, leaving a strong crust as a gift. Up until present there were no snowpack concerns below the Thanksgiving crust and in general new snow received post-Thanksgiving has reportedly bonded well.
A series of frontal systems produced snow over the week following the Thanksgiving warm period: Hurricane Ridge received about 2 feet of snow.
Fair weather Sunday through Tuesday has allowed the layers in the north-facing terrain to consolidate and heal significantly. On Wednesday, significant warming was observed at Hurricane Ridge and temperatures warmed to 47F and are continuing to remain high as the sun sets. ESE winds were in the low 10's, gusting to 20 throughout the day.
Observations
NWAC Professional Observer Matt Schonwald was in the Hurricane Ridge area on Wednesday. On Wednesday, south-facing terrain was warming significantly in due to solar warming and increasingly entraining deeper snow (up to 50-60 cm) as the day progressed. Some natural large (D2) loose wet slides were entraining enough snow to break wood.
Schonwald reports that a previously unreported avalanche cycle on Sunday produced up to D2 skier-triggered and natural storm slab avalanches. On Wednesday, that same storm slab layer 20 cm down was still slightly reactive in compression on North-facing terrain, but does not propagate. Wind-deposits were shallow (less than 10 cm) on northerly terrain, with no ability to propagate and triggering possible in isolated terrain features.
Avalanche 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: East, South East, South, South West, West.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 1 - 1
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, West, North West.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 1