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Avalanche Forecast

Archived

Mar 16th, 2016–Mar 17th, 2016

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

Regions

Mt Hood.

Dangerous avalanche conditions should persist in all elevation bands in the Mt. Hood area Wednesday. Storm slabs may become locally sensitive Wednesday morning as new snow settles and becomes more cohesive. Loose wet avalanches will become likely during sunbreaks Wednesday afternoon on steeper solar aspects and my entrain copious amounts of new snow. Wind slabs will be found in the above treeline band on lee aspects. 

Detailed Forecast

Wednesday morning update: The avalanche danger has been changed to CONSIDERABLE in the Mt. Hood area in the below and near treeline bands because human triggered avalanches are likely and natural avalanches are possible.Storm slabs may become locally sensitive Wednesday morning as new snow settles and becomes more cohesive. Loose wet avalanches will become likely during sunbreaks Wednesday afternoon on steeper solar aspects and my entrain copious amounts of new snow. 

Previous discussion: Recent or new wind slabs will remain the main avalanche problems Wednesday in the Mt Hood zone.

New wind slab is mostly likely to be found on N-SE facing slopes. Stiff wind transported snow and snowpack cracking can be good signs of wind slab slab instabilities.

Cloudy cool conditions Wednesday may limit the possibility of loose wet snow but the sun is gaining power so watch for the possibility of loose wet snow on solar slopes if extended sun breaks occur. 

The avalanche danger should gradually decrease Wednesday with less wind and slow settlement and stabilization of new snow and fairly cool temperatures. 

Snowpack Discussion

Weather and Snowpack

Storms have moved across the Northwest at a nearly daily frequency the past few weeks with fluctuating but generally moderate snow levels.

Two deep surface low-pressure systems moved across the Olympic Peninsula with the first passing last Thursday and the next on Sunday. These systems caused very stormy weather.  

Cool showery weather Monday and Tuesday with continuing moderate westerly winds have deposited additional snow in showers at lower temperatures.

New storm amounts on Mt Hood have been impressive for March, mostly about 18 inches each of the past two days with 2-3.5 feet of storm snow since Thursday!

Strong winds and recent storms have created widespread wind and storm slab problems, creating dangerous avalanche conditions.

The mid and lower snow pack at Mt Hood should generally be a stable mix of crusts and layers of moist and rounded snow crystals.

Recent Observations

The Mt Hood Meadows pro-patrol on Sunday reported stormy conditions with widespread wind and storm slab of 6-12 inches on all aspects in the area, easily triggered by ski cuts and running on the crust buried on Thursday.

On Monday and again Tuesday, control performed by Mt. Hood Meadows pro-patrol produced extensive and sensitive wind and storm slab avalanches triggered by ski cuts in lower elevation slopes and explosives in wind loaded terrain. Avalanches were greatest on N-E facing terrain. 

Loose wet slides were releasing on solar aspects by Tuesday afternoon below 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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

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.