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Avalanche Forecast

Archived

Mar 1st, 2016–Mar 2nd, 2016

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 unlikely, human triggered possible.

Regions

Mt Hood.

With several avalanche problems to deal with Wednesday, conservative terrain selection will be essential to stay safe because human triggered avalanches are still likely. Choose moderately angled terrain and avoid wind loaded slopes, saving those steeper lines for another day.

Detailed Forecast

Showers should wind down Wednesday morning with the next frontal system already moving in later Wednesday afternoon. Despite a modest cooling trend, storm related danger will continue through Wednesday due to strong southwest or west winds loading lee slopes during moderate showers Tuesday night. 

Wind slab will continue to build Tuesday night on lee slopes with moderate to strong southwest to west transport winds. Wind slab will be dense and pocketed due to the strength of the winds and also more likely to be found further downslope than usual. 

Storm slab instabilities should be healing but may still be sensitive Wednesday in less wind affected areas mainly below treeline.  

Loose wet avalanches will become more likely on steeper slopes in the afternoon as snow levels begin to rise once again. Avalanches that begin in the new snow may become larger lower down the path as they entrain moist or wet snow.  

With several avalanche problems to deal with Wednesday, conservative terrain selection will be essential to stay safe because human triggered avalanches are still likely. Choose moderately angled terrain and avoid wind loaded slopes, saving those steeper lines for another day.

Non-avalanche hazard: Despite our seasonally healthy snowpack, many creeks are open and difficult to cross due to the periodic warm temperatures and rain events.  

Snowpack Discussion

Weather and Snowpack

Springlike weather under high pressure Feb 23rd and 24th led to abundant sunshine with daytime highs climbing into the 40's and 50's. The fair and mild weather caused thick surface crusts, especially on solar slopes in most areas by Friday. A weak front brought quite a bit of mostly rain to Mt Hood Friday night to Saturday morning.

A strong Pacific frontal system blew through the Cascades mid-day Sunday. Significant transport winds were from the W-SW and seen in the early afternoon post-frontal passage with gusts in the 40s or 50s near treeline with gusts recorded above 100 mph at the Mt. Hood Meadows Cascade Express station (7300 ft)! 

A warm front quickly dropped up to 6 inches of new snow early Tuesday morning at NWAC Mt. Hood stations before changing to rain. After a late morning lull, precipitation rates increased again in the afternoon as the cold front approached and snow levels began lowering. Not to be outdone by Sunday's system, gusts near 150 mph were recorded at the Cascade Express station (7300') Tuesday afternoon! 

The mid and lower snow pack along the west slopes should be a stable mix of crusts and layers of moist and rounded snow crystals.

Recent Observations

No avalanches were observed on Sunday near and below treeline. Winds were too strong for any person not directly anchored to the mountain to make observations above treeline. 

On Monday, Mt. Hood Meadows pro-patrol noted some 1-2' soft wind slabs on N-NE slopes above treeline during control work with very small storm slabs noted as well. 

Observations were limited Tuesday but rain runnels were noted up to 6800 feet. At 6200', the top 30 cm of snow was wet. Mt. Hood Meadows pro-patrol noted 6-8" loose wet avalanches sensitive to ski cuts on steeper east aspects above 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.

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.