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Avalanche Forecast

Archived

Dec 4th, 2017–Dec 5th, 2017

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Mt Hood.

Watch for mostly small wind-loaded pockets on steeper terrain, particularly above treeline.  Approach ridges with caution and watch for firmer wind-transported snow.  Storm slab is less likely, but continue to evaluate the upper snowpack as you travel.

Detailed Forecast

Mostly sunny and mild Tuesday. Light winds.

This will allow further stabilizing of recent wind and storm slab layers. 

Early season terrain hazards still exist, such as poorly covered rocks, vegetation and creeks, particularly at lower elevations.

Snowpack Discussion

Warm, wet weather before Thanksgiving caused wet snow and glide avalanches as well as significant snowpack consolidation. There are no snowpack concerns below the Thanksgiving crust and new snow received post-Thanksgiving has reportedly bonded well.

A series of frontal systems produced snow over the past week since the Thanksgiving warm period: NWAC stations at Mt. Hood received 20-23" of snow.

This includes the recent snow accumulation for the 48 hours ending on Sunday, December 3 at NWAC stations of 7-8".

Winds at the top of Mt. Hood Meadows (Express Station), winds on Sunday were in the 20's with gusts mostly in the 50's to 70's. This built wind slab layers as evident Monday morning of a natural wind slab release sometime Sunday night. See image below

Observations

On Saturday, the Mt. Hood Meadows Ski Patrol reported 13” of increasing density snow over an impenetrable Thanksgiving crust. Tests gave no results on an east-facing slope at 6600 ft.

On Sunday, the Mt. Hood Meadows ski patrol found sensitive low-density 8-10" small, ski-triggered wind slab on specific, isolated ridge-top features near treeline.

On Monday, Patrol at Hood Meadows saw evidence of a natural wind slab that released after dark Sunday.

 

Natural wind slab release sometime Sunday night, 12/3. ESE facing wind loaded slope about 6600 feet. Photo: Brian Murphy

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.