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Archived

Avalanche Forecast

Jan 21st, 2015–Jan 22nd, 2015
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low

Regions: Mt Hood.

The weather should have limited effects on snow conditions on Thursday. Mainly watch for lingering areas of firmer wind slab on previous lee slopes.

Detailed Forecast

A weak dissipating front should move through an upper ridge and across the Northwest on Thursday. This may cause some light rain or snow at Mt Hood with a minor drop in snow levels.

This weather should have limited effects on snow conditions at Mt Hood.

Mainly watch for lingering areas of firmer wind transported snow and wind slab on previous lee slopes from the back end of the storm early this week.

New snow amounts should be limited on Thursday and any new wind slab should be unlikely, shallow and small if any.

Loose wet avalanches will not be indicated due to the cloud cover and cooling. Storm slab will also not be listed due to the expected limited amounts of new snow. 

Snowpack Discussion

Strong southwest flow carried a warm and wet front across the Northwest Saturday night. This front tapped subtropical moisture pushed snow levels pretty high and resulted in 3.5 - 4.5 inches of rain at NWAC sites at Mt Hood. A cooling trend Sunday along with another inch of water gave 4-5 inches of new snow between 5-6000 feet by Monday morning. 

NWAC pro-observer CJ Svela was at Timberline on Sunday and reported 1-3 inches of new snow over a breakable crust. Melt freeze layers in the mid pack seemed to lack consistent shears and tests did not indicate propagation.

The Meadows patrol reported wind transport Sunday night and Monday morning leading to a thin wind slab above treeline producing small but regular releases during control work on lee slopes around 7000 feet. But west winds eased off more quickly than forecast Monday and new wind transport was likely not significant. By Wednesday they reported no avalanches and generally shallow recent snow over deep firm snow.

Some sun with mild temperatures is being seen at Mt Hood Wednesday. Small loose wet avalanches might be possible on steep solar slopes.

The mid and lower snowpack at Mt Hood should also mainly consist of melt-freeze crusts and stabilized rounded grain layers from warm stretches so far this winter. 

Avalanche Problems

Wind Slabs

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.

 

Wind Slabs form in specific areas, and are confined to lee and cross-loaded terrain features. They can be avoided by sticking to sheltered or wind-scoured areas..

 

Wind Slab avalanche. Winds blew from left to right. The area above the ridge has been scoured, and the snow drifted into a wind slab on the slope below.

 

Wind slabs can take up to a week to stabilize. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind scoured areas.

Aspects: North, North East, East, South East.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 1 - 1