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Avalanche Forecast

Archived

Mar 14th, 2016–Mar 15th, 2016

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
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.

Back country travel is not recommended in avalanche terrain near and above treeline at Mt Hood on Monday. Conservative decision making will be a good plan in the below treeline and the avalanche forecasts will get refined after new information becomes available on Monday.

Detailed Forecast

Additional showers are expected Tuesday at continued cool temperatures. Showers should generally be fewer and taper by late Tuesday. 

Moderate west winds at ridge level should persist Tuesday before diminishing late Tuesday. 

Recent or new wind and storm slabs will remain the main avalanche problems Tuesday 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 or storm slab instabilities.

New storm slab is likely in areas where new snow rapidly accumulates for more than several hours.

Cloudy cool conditions Tuesday 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 Tuesday 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.

A storm last Wednesday and Thursday caused a warming trend that peaked Wednesday night with rain received at least up to 6600 feet on Mt Hood or just above treeline along with very strong west winds. About 8 inches of snow accumulated on a new crust at Mt Hood for the two days ending Thursday morning.

A front on Saturday caused west-southwest winds and another 4-6 inches of snow at Mt Hood ending Sunday morning.

A deep surface low-pressure system moved across the region Sunday causing very stormy weather. 

Cool showery weather Monday with continued moderate westerly winds continues to deposit additional snow at lower temperatures.

New storm amounts on Mt Hood range from about 15-30 inches deposited in the past 36 hours as of Monday evening.

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

On Thursday, NWAC pro-observer Laura Green toured in the Mitchell and Heather drainages and found evidence of rain up to at least 6600 feet. A supportable rain crust and rain runnels were observed below 6000'.

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, 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. 

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.

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.