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Avalanche Forecast

Archived

Jan 5th, 2016–Jan 6th, 2016

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

A variety of avalanche problems are expected on Wednesday including storm slab, wind slab and loose wet snow avalanches. Evaluate snow and terrain carefully at Mt Hood on Wednesday.

Detailed Forecast

A large weak low pressure system will drift toward California on Wednesday. A shot of drier air with some weak light showers should eject from the low and over the Northwest. But slightly warmer temperatures should be seen in most areas.

The storm snowfall of about 10 inches at Mt Hood will lay over the rain crust from Monday. This should make triggered storm slab possible on Wednesday. Small triggered avalanches on varied steep slopes should be expected Wednesday.

Mostly older wind slab will still need to be watched for on a variety of aspects. Wind slab from over the weekend is most likely on west aspects. Look for signs of firmer wind transported snow that can indicate wind slab layers.

Some sun or solar effects and slightly warmer temperatures should also be seen on Wednesday. Loose wet avalanches seem like a possible bet as well on steep solar slopes. Watch for wet snow deeper than a few inches and initial natural small loose wet releases on solar slopes that usually precede loose wet avalanches.

Snowpack Discussion

Fair weather was seen for almost a week around the New Year. This weather caused lots of consolidation and stabilizing of the heavy snow from December.

By New Years Eve through the weekend moderate to strong east-northeast winds had significantly scoured or transported available surface snow onto lee west aspects, mainly in the near and above treeline elevation bands.

NWAC pro observer Laura Green was in the Newton Creek drainage Friday and found good skiing in non-wind affected terrain. Even on wind loaded slopes near treeline, the denser wind slab was bonding to underlying snow and no natural or skier triggered avalanches were noted. Significant wind loading continued to occur on the upper mountain Friday and to lesser extent Saturday.

Surface snow sculpted by wind and active wind transport. Photo: Laura Green

On Monday the Mt Hood Meadows pro patrol reported warming and a widespread 1 cm freezing rain crust up to 7000 feet.

Laura was out again near the Mt Hood Meadows ski area on Tuesday and reported 5 inch sensitive small storm slab on steep slopes of varied aspects in all 3 elevations bands. These storm slabs were releasing on the rain crust from Monday.

Storm snowfall for the Sunday night to Tuesday period should be in the 10 inch range at Mt Hood by Wednesday morning.

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.

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.

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.