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Avalanche Forecast

Archived

Dec 26th, 2016–Dec 27th, 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 and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

Mt Hood.

Very dangerous avalanche conditions are expected in much of the terrain Tuesday. Storm and wind slabs will be sensitive Tuesday. The safest plan is to avoid avalanche terrain of consequence until unstable layers stabilize. 

Detailed Forecast

Stormy conditions Monday night and Tuesday will cause an increasing avalanche danger!

New storm and wind slabs will build through Tuesday. Storm or wind slabs will likely be the most sensitive in areas where poorly bonded to an underlying crust.   

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. 

NW winds near and above treeline were moderate at Mt. Hood Friday night through mid-day Saturday.  Christmas Day was partly to mostly sunny with light winds and cold temperatures.

The winds increased to moderate to strong Monday afternoon ahead of the arriving frontal system.  

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.

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.