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Avalanche Forecast

Archived

Dec 3rd, 2017–Dec 4th, 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 cautiously and watch for firmer wind-transported snow.  Storm slab is less likely, but continue to evaluate the upper snowpack as you travel.

Detailed Forecast

Decreasing clouds and decreasing NW winds should be seen on Monday at Mt. Hood.

Wind slab is replacing storm slab as our primary avalanche problem as storm snow will be more rapidly stabilizing. Small to large wind slabs should remain most likely on NW through S aspects on Monday and should become less sensitive to trigger. Watch for areas of firmer, wind-transported snow mainly on lee terrain features. 

Storm slab layers in the upper snowpack are still giving test results at multiple locations along the west slopes of the Cascades on Sunday. Similar snow layers may be present, but less likely at Mt. Hood due to lower precipitation intensities. These layers should continue to heal where present on Monday.

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 December 3 at NWAC stations of 7-8".

Since last Monday, temperatures at NWAC Mt. Hood stations have generally been steady in the upper 10's and  20's at higher elevations and winds have been mostly SW to W in the teens and 20s. However, at the top of Mt. Hood Meadows (Express Station), winds on Sunday have been in the 20's with gusts mostly in the 50's to 70's.

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.

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.