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Archived

Avalanche Forecast

Feb 5th, 2017–Feb 6th, 2017
Alpine
4: High
The avalanche danger rating in the alpine will be high
Treeline
4: High
The avalanche danger rating at treeline will be high
Below Treeline
3: Considerable
The avalanche danger rating below treeline will be considerable
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate

Regions: Mt Hood.

Backcountry travel in avalanche terrain is not recommended near and above treeline Monday on Mt. Hood. Below treeline, choose conservative terrain such as lower angled slopes while watching for firmer wind transported snow in all elevation bands.  

Detailed Forecast

We are going to keep the snow tap turned on for one more day with additional light to moderate snowfall Sunday night followed by a sharp cooling trend and light to moderate showers on Monday.

Strong SW winds will continue to load lee primarily NE-E aspects near and above treeline. Westerly winds will increase Monday likely transporting snow to lee aspects even below treeline. Storm slab sensitivity may peak Sunday night but may continue to be touchy on Monday. While deeper storm slab instabilities should be healing, it is still possible to trigger a large storm slab avalanche in isolated areas. 

New snow instabilities will need more time to settle out in this zone so make conservative terrain choices by choosing lower angled terrain and avoiding avalanche terrain near and above treeline. 

Snowpack Discussion

Weather and Snowpack

Strong NE-E winds were seen Wednesday and Thursday with very cold temperatures. Fresh, touchy wind slabs formed with large plumes of snow visibly transporting loose snow from exposed terrain.

A storm cycle began Friday with generally 2 feet of snow accumulating at NWAC stations on Mt. Hood through Sunday morning. A warming trend was seen Sunday afternoon with a break in the precipitation. Moderate W-SW transport winds were recorded near and above treeline for much of the weekend.

Recent Observations

NWAC pro-observer Laura Green was out near Barlow Pass on Friday at 4100-5200 feet and found limited wind transport, low quality shears in tests in the upper snowpack and no direct signs of instability. 

Mt. Hood Meadows pro-patrol had a busy day on Saturday with sensitive but generally shallow storm slabs easily releasing during control on a density change in the storm snow. Wind loaded NE slopes between 5500-6500 ft ran well during control work with crowns locally up to 2'.  

On Sunday morning Meadows pro-patrol found storm slabs on all aspects of about 1 ft that were especially sensitive below treeline. E-NE aspects were being continuously loaded near and above treeline throughout the day. 

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, North West.

Elevations: All elevations.

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: Likely

Expected Size: 1 - 1