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Avalanche Forecast

Archived

Mar 2nd, 2017–Mar 3rd, 2017

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

Fresh wind slab will build on lee easterly aspects near and above treeline, but expect cross-loading due to the strength and duration of the winds. New wind loading will create dangerous avalanche conditions mainly near and above treeline Friday. 

Detailed Forecast

Mt. Hood will be spared the heavier precipitation seen further north but not the strong winds or warming trend.  Light rain or snow should develop overnight and increase by Friday late afternoon and evening as a cold front sweeps through. Moderate to strong southwest winds will increase Thursday night and stay elevated through Friday night.   

Fresh wind slab will build on lee easterly aspects near and above treeline, but expect cross-loading and wind slab formation band due to the strength and duration of the winds. New wind loading will create dangerous avalanche conditions near and above treeline Friday. 

Shallow storm slab should build and become more reactive late Friday afternoon due to increasing snowfall paired with a warming trend.  

Generally shallow loose wet avalanches are possible below treeline due to rainfall at lower elevations. 

Snowpack Discussion

Weather and Snowpack

The most recent wet warm storm arrived on Valentines Day 2/14 and formed the uppermost very strong rain crust in our snowpack. 

A stronger than forecast storm late Monday through Tuesday deposited 2 - 2.5 ft of snow by Tuesday evening. The heavy snowfall arrived with very strong westerly alpine winds which gradually decreased on Wednesday.

Thursday began mostly sunny but increasing clouds were seen in the afternoon. SW winds above treeline increased and become were very strong Thursday afternoon, with a gust above 100 mph at 6 PM recorded at the Cascade Express weather station at Mt. Hood Meadows.  

Recent Observations

Several contacts were made with the Mt Hood Meadows patrol through the day Tuesday and they reported widespread natural and triggered wind and storm slabs especially near and above treeline. Avalanches were occurring even on relatively low angled terrain. Over 2 feet of new snow had accumulated by early Tuesday with more snow received through the day. Low visibility limited additional observations but by Tuesday afternoon large hard wind slabs were developing above treeline and several sympathetic avalanches were triggered. The recent relatively stable snowpack had quickly turned into very dangerous avalanche conditions.

By Wednesday conditions had improved and the Mt Hood Meadows patrol reported sunny but windy conditions with windward slopes getting scoured and local size-able wind slab building on lee slopes. The lower mountain was showing signs of spring with rollerballs and small triggered loose wet avalanches.

On Thursday Laura Green reported that a sun crust had formed on solar slopes. She passed along that several natural hard wind slab avalanches had occurred in White River Canyon above treeline on E-NE aspects with crown depths up to several feet. These hard slab wind avalanches likely occurred on Wednesday.  

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.