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Archived

Avalanche Forecast

Feb 5th, 2016–Feb 6th, 2016
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
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 wind and storm slab layers should be seen on Saturday. The skiing should be improved but don't forget to make careful snowpack evaluations.

Detailed Forecast

Strong southwest winds aloft will accompany a cold front will cross the Northwest on Friday evening. West winds will follow with orographic snow showers and a good cooling trend on Saturday morning.

The cooling trend may help bond new snow to old snow surfaces where the snow starts at above freezing temperatures. With a little luck Hurricane will have several inches or better of new snow by the time snow showers taper off on Saturday.

The main avalanche problem should be new wind slab on lee slopes in the near and above treeline. Watch for signs of snowpack cracking and firmer wind transported snow on lee slopes.

A secondary avalanche problem should be new storm slab in areas with less wind if there is rapid loading. The cooling trend may help limit this avalanche problem.

 

 

Snowpack Discussion

The last heavy rain fell in the Olympics January 27th-28th with over 2 inches of rain recorded at the NWAC station at Hurricane Ridge.

The "20th of June" path released as a wet slab during the rain and warmth January 27th. Photo: January 29th by Matt Schonwald.

A strong occluded front with strong winds crossed the Northwest January 29-30th. Hurricane Ridge had about 14 inches snowfall.

NWAC pro-observer, Matt Schonwald visited Hurricane January 29th and found rapidly building wind slab and extensive loading on lee slopes in all 3 elevation bands. New cornices were sensitive to triggering but still relatively small. 

Cool, benign weather followed Sunday through Tuesday. A sun crust formed on many solar slopes and surface hoar was seen on many non-solar slopes in the Cascades so this is possible in the Olympics as well.

A cold front and then a warm front crossed the Northwest on Wednesday and Thursday. The Hurricane ranger reported about 8 inches of snowfall for the 2 days ending Friday morning.

Hurricane Ridge was living up to it's name today and unfortunately the road was closed due to storm conditions and NWAC pro-observer Matt Schonwald could not make it up to the Ridge.

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: 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: Possible

Expected Size: 1 - 1