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Avalanche Forecast

Archived

Dec 21st, 2017–Dec 22nd, 2017

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Olympics.

Watch for recent wind transported snow below exposed ridges or any wind stiffened surface snow, making slab avalanche releases possible. Avoid large open slopes of consequence in higher terrain. Keep eyes on partners at all times when traveling in terrain with deep unconsolidated snow, where a snow immersion hazard may exist.

Detailed Forecast

A weak disturbance is expected to bring clouds and light snowfall across the Olympics overnight Thursday, decreasing Friday. Only light amounts of new snow are expected and should not cause an increase in danger. Moderate NW winds at higher elevations may continue to transport available snow, building areas of wind slab on a variety of a-typical aspects from east to southwest facing. 

While the overall danger should continue to decrease, continue to travel with caution and watch for any slab like structure or cohesion in the upper snowpack, indicating the possibility of slab avalanches propagating.   

Watch for touchy recently formed cornices and keep a safe margin along ridges and slopes below.

Most areas now have deep unconsolidated recent storm snow and this has created a non-avalanche, snow immersion, tree-well hazard in places. Keep partners in sight at all times when traveling in terrain with deep unconsolidated snow.

Snowpack Discussion

Recent deep storm snow has been settling and stabilizing Wednesday and Thursday under fair cool weather. This has allowed for storm related weak layers to settle with no reported storm slab avalanches reported since Tuesday.

Moderate to strong northerly crest level winds have been transporting snow on many exposed ridges both Wednesday and Thursday. This should have built areas of wind slab on a variety of aspects, including non-typical southerly facing slopes near and above treeline.

A strong storm from late Monday through Tuesday afternoon dropped over 3 inches of water equivalent amounting to over 2 feet of new snow in the Hurricane Ridge area by early Wednesday. Strong winds with warmer initial temperatures likely built wind and storm slabs by Tuesday.

The storm snow fell on settled old snow or crust layers formed during the long period of high pressure in early December. 

Observations

No recent observations.

Problems

Wind Slabs

Wind Slab avalanches are the 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.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). 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.