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Avalanche Forecast

Archived

Dec 2nd, 2017–Dec 3rd, 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.

Storm slab will be possible on steeper slopes that rapidly accumulate more than a few inches of new snow. Wind slab may be encountered on Sunday near ridges and may be triggered particularly on steeper terrain.

Detailed Forecast

Light to moderate showers Saturday and Saturday night should give way to light showers on Sunday. Increasing moderate WNW winds are expected on Sunday and should be capable of transporting snow, especially near ridges and exposed terrain. See the NWAC mountain weather forecast tab for more details. 

Five to ten inches of new snow Saturday to Sunday morning should be sufficient for the development of new areas of storm slab. Increasing winds should transport this new and older snow and create pockets of wind slab, particularly near ridges and on NW through S aspects.

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 in general new snow received post-Thanksgiving has reportedly bonded well throughout the range. 

During the week, a series of frontal systems have generally produced light amounts of new snow for the Mt. Hood area, with 14-16" over the past six days. Temperatures during this time period have been mostly in the 20's at Mt. Hood with SW to W winds in the 10's and 20's at Mt. Hood Meadows.

Observations

On Wednesday, a professional ski patroller from Mt Hood Meadows toured to about 6600 feet, finding about 8-12" of recent storm snow well bonded to the crust from last week. Storm snow was deepest on N-E facing terrain and no avalanches were noted. Some rollerballing was noted on steep solar terrain due to direct sun warming.   

On Friday, NWAC observer Laura Green reported no new avalanche or snowpack concerns near and below treeline, with possible isolated pockets of wind slab above treeline. Laura noted that despite moderate winds above treeline, there was not much available snow for transport. 

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.

Problems

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.

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.