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Avalanche Forecast

Archived

Feb 6th, 2017–Feb 7th, 2017

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

Mt Hood.

New snow instabilities within the deep recent snowfall will continue to settle out, but continue to make conservative terrain choices by choosing lower angled terrain and avoiding wind loaded slopes. Recently formed wind slabs are likely on mainly any east facing slopes, especially below ridges.  Travel with deep snow safety precautions in place.

Detailed Forecast

Strong SW winds will continue to load lee primarily NE-SE aspects near and above treeline Monday night. Showers should end or become widely scattered Tuesday morning. Cold temperatures and decreasing winds are expected Tuesday. This should allow for slow settlement and stabilization of recent wind and storm slabs formed during the storm cycle since Friday. However, new fresh wind slabs may still be touchy Tuesday. 

Storm slabs may still be sensitive on Tuesday, but likely confined to the most recent storm snow over the past day. While deeper storm slab instabilities should be stabilizing, it may still be possible to trigger a large storm slab avalanche in isolated areas. 

The unconsolidated snow is deep, so being aware that loose dry avalanches triggered on steep slopes can entrain substantial snow.   

Instabilities within the deep new snow may need more time to settle out so make conservative terrain choices by choosing lower angled terrain and avoiding any wind loaded slopes, mainly near and above treeline. 

Note that deep snow conditions now exist in most terrain. Travel with a partner and use good communication and keep your partner in view at all times. 

Snowpack Discussion

Weather and Snowpack

A strong storm cycle began Friday with 3-4 feet of snow recorded at the Mt Hood area stations on average, through Monday afternoon. A warming trend affected all areas Sunday. Moderate W-SW transport winds were recorded near and above treeline for much of the weekend. Strong westerly winds persisted Monday. 

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. 

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.