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Archived

Avalanche Forecast

Jan 17th, 2015–Jan 18th, 2015
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.

Sunday should be fairly stormy day at Hurricane. New storm and wind slab layers are likely.

Detailed Forecast

A wet cold front will cross the Northwest Saturday night. Snow levels will be highest on Saturday night. A good period of southwest-west flow, moderate to heavy orographic snow showers, and cooling with lowering snow levels should be seen on Sunday. New snow at Hurricane by the end of the day Sunday may be 5-10 inches.

Building storm slab is likely mainly near and above treeline on Sunday. Watch for cracking and releases on steep sheltered slopes where snowfall exceeds an inch an hour for more than a few hours.

Building wind slab is also likely mainly near and above treeline on Sunday. Watch for firmer wind transported snow on lee slopes.

The cooling should cause some good snow conditions on other slopes. Don't let powder starvation change plans to stick to safe slopes on Sunday. It is always a good plan to give new snow layers a day to stabilize before venturing to steeper slopes after a storm.

Snowpack Discussion

A front late Thursday was followed by showers Friday. At Hurricane this only gave up to about 3 inches of storm snow.

NWAC observer Tyler Reid was at Hurricane on Friday. He painted a somewhat dismal picture with shallow or little snow on most slopes. He noted the unlikely potential for small wind slab on lee slopes but there was not an avalanche danger in most places.

In areas of the Olympics with significant snow the underlying mid and lower snowpack should mainly consist of melt-freeze crusts and stabilized rounded grain layers. This is due in great part to the warm and dry period from about 6-15 January and previous similar periods so far this winter. Persistent weak layers are not expected in the Olympics.

The overall snowpack remains well below normal for this time of year in the Olympics.

Avalanche Problems

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: Alpine, Treeline.

Likelihood: Likely

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, South East.

Elevations: Alpine, Treeline.

Likelihood: Likely

Expected Size: 1 - 1