Avalanche Forecast
Regions: Olympics.
Travel in avalanche terrain near and above treeline is not recommended along the east slopes on Monday. Potential dangerous avalanche conditions are expected below treelinge where cautious route finding and conservative decision making will be essential on Monday.
Detailed Forecast
Strong west flow will carry a strong cold front across the Northwest Sunday night and Monday morning. This should cause strong alpine winds with moderate to heavy snow with a warming trend. The warming trend should contribute to the formation of both new wind slab and new storm slab layers.
New wind slab is very likely in the Olympics on Monday. Wind transport will deepen these layers mainly on lee north to southeast slopes but new wind slab is possible on other aspects.
New storm slab is also very likely in the Olympics on Monday on any slopes that rapidly accumulate new snow of more than a several inches.
Potential dangerous avalanche conditions are expected in the Olympics on Monday.Â
Another strong front should be seen Monday night and Tuesday. This should maintain or increase the avalanche danger in the Olympics and Cascades.
Snowpack Discussion
Weather and Snowpack
The last storm cycle to affect the Olympics and most of the Washington Cascades was about Thursday, December 8th to Monday morning, December 12th. About 3 feet of snowfall was seen at the NWAC station at Hurricane.
There has been a lot of snowpack settlement since the last storm cycle ended, allowing this underlying snow to mostly stabilize.
Clear or fair and cold weather has been seen about Wednesday, December 14th to Sunday, December 18th . This caused widespread surface hoar and near surface faceted snow to develop in the Olympics and Cascades. Thin sun crusts have also formed on steeper solar slopes. These layers are expected to act as widespread weak layers or sliding surfaces for the upcoming moderate to heavy snowfall.
Recent Observations
NWAC pro-observer Matt Schonwald was at Hurricane on Friday and found a mostly right side up snowpack. The December 8th layer was found at a depth of 30 cm but gave moderate to hard compression tests and did not show signs of propagation. Isolated small wind slab was found on NE slopes above 5000 feet. He noted widespread large surface hoar and near surface faceted snow.
Surface hoar at Hurricane Ridge on December 16th. Photo by Matt Schonwald.
An observation for Hurricane for Saturday via the NWAC Observations page indicated surface hoar and near surface faceted snow in sheltered a spot sheltered from the sun. But perhaps not as widespread as seen by Matt Schonwald on Friday.
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: Very Likely
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: Very Likely
Expected Size: 1 - 1