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Avalanche Forecast

Archived

Feb 5th, 2017–Feb 6th, 2017

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

Regions

Mt Hood.

Backcountry travel is not recommended near and above treeline Sunday on Mt. Hood. Below treeline, choose conservative terrain such as lower angled slopes while watching for firmer wind transported snow down into the below treeline band during the afternoon.  

Detailed Forecast

More snow is on the way Saturday night and Sunday with a gradual cooling trend forecast. W-SW transport winds will continue on Sunday and are forecast to become very strong on the upper mountain Sunday afternoon.  

Despite a slight cooling trend, new and recently formed storm slabs should still be sensitive Sunday. While storm slabs are most likely to release within the most recent storm layers, various crusts are capable of providing bed surfaces for larger avalanches. 

We've highlighted more traditional lee easterly aspects on the elevation/aspect diagram, but be aware that strong winds on the upper mountain Sunday afternoon may create unusual loading patterns as well as load lee aspects much further downslope than usual. Large natural and human triggered wind slab avalanches will be possible on lee aspects near and above treeline.  

Backcountry travel is not recommended near and above treeline Sunday on Mt. Hood. Below treeline, choose conservative terrain such as lower angled slopes while watching for firmer wind transported snow down into the below treeline band during the afternoon.  

 

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 1 foot of snow accumulating at NWAC stations on Mt. Hood. Except for a band of freezing rain on the lower mountain Saturday morning, snow levels gradually warmed into the 4000-5000 foot range by Saturday afternoon.  Moderate W-SW transport winds were recorded near and above treeline for much of Friday night and Saturday.

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'.  

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.