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Avalanche Forecast

Archived

Dec 27th, 2016–Dec 28th, 2016

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.

Very dangerous avalanche conditions persist in much of the terrain. Storm and large wind slabs will be sensitive Wednesday. The safest plan is to avoid avalanche terrain of consequence until the storm and wind slabs stabilize. 

Detailed Forecast

Stormy conditions Tuesday night should gradually ease by Wednesday as a brief break in storms occurs through the day Wednesday. Light winds and a lack of significant additional snowfall should allow for a gradual decrease in danger. However, cold temperatures will limit the stabilization Wednesday.

Storm or wind slabs will be widespread and continue to be sensitive to trigger Wednesday. The current storm slabs may be weakly bonded to a slick crust formed last week. In wind loaded areas, some large to very large avalanches are likely!

Avoid travel in avalanche terrain of consequence Tuesday.

 

 

 

Snowpack Discussion

Weather and Snowpack

Strong storms a week ago Sunday and Monday deposited generally 3 inches of water equivalent recorded at NWAC stations on Mt Hood through early Tuesday morning. 

Unfortunately, much of the heavy precipitation fell in liquid form with rain reaching above 7000 feet by Tuesday morning. 

A sharp cooling trend mid-day Tuesday and showers deposited about 2 inches of snow.  A strengthening rain crust was noted near and below treeline by late in the day Tuesday with the arrival of colder air.  

A front Thursday and upper trough on Friday with low snow levels deposited about 5 inches of snow at NWAC stations on Mt Hood. 

Christmas Day was partly to mostly sunny with light winds and cold temperatures.

A strong front moved into the region Monday afternoon, passing Mt Hood early Tuesday, followed by heavy snow showers and strong westerly winds through the day Tuesday at low snow levels. Storm total snow from Monday morning through Tuesday afternoon have been over 2 feet and still snowing Tuesday evening!

Recent Observations

Reports from the Mt Hood Meadows pro-patrol Wednesday reported a significantly different snowpack following rain, avalanches and cooling. A stout surface crust was found on all elevations up to at least 7200 feet. On exposed terrain, the crust was very supportable while in treed terrain the crust ranged from breakable to supportable.

The Meadows patrol checked in early Sunday morning to report NW winds had scoured windward aspects near and above treeline exposing the thick crust on many aspects. The crust was slick enough that Santa had trouble landing his sled on any slope steeper than 20 degrees.

Patrol at Mt Hood Meadows Tuesday, reported very sensitive storm slab releases, with slabs releasing upon approach to ridges or steeper features. 

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.