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Archived

Avalanche Forecast

Dec 9th, 2015–Dec 10th, 2015
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate

Regions: Olympics.

New shallow wind slab will be the focus on Wednesday at Hurricane Ridge as the previous wet snowpack begins to strengthen and refreeze. Careful snow evaluation and cautious route finding should be essential if you venture above treeline.

Detailed Forecast

The strong warm front is expected to pass by early Wednesday with cooling and a period of moderate precipitation along with continued strong winds.

Further cooling and lighter showers are expected later Wednesday with strong southwest winds shifting to strong westerly winds.

This weather will cause a transition in the snowpack from wet snow to a gradually draining and refreezing upper snowpack. Cooling should change rain to snow by Wednesday with new shallow snow building on the refreezing snowpack. This should form a good bond of new snow. Continued strong winds are likely to transport new snow and form some wind slab layers on lee slopes below ridges. 

 

 

Snowpack Discussion

We have not specific snowpack observations from Hurricane Ridge so far this season. However, the park ranger reported moderate rain Tuesday morning with a snowdepth of 24 inches at the Hurricane Ridge study plot. Given the warm and very wet weather over the past few days, it is very likely that the upper snowpack has become saturated and well drained by now over most Olympic Mountain sites. Heavy dense wet snow likely overlies a strong melt-freeze crust from mid-November. The high danger associated with this scenario has likely now played out, however continued caution and close snowpack observations are warranted as we transition back to a firm base as temperatures cool and surface snow gradually refreezes.

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.

Likelihood: Possible

Expected Size: 1 - 1