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Avalanche Forecast

Archived

Feb 26th, 2017–Feb 27th, 2017

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.

Watch for recent wind slab on lee easterly aspects. Fresh wind slab should be found near and above treeline. Be aware that the winds above treeline are forecast to increase Monday afternoon and should continue loading the same lee easterly aspects during the latter part of the day.

Detailed Forecast

A weak low pressure system moving south along the Washington Coast on Monday should produce light snow showers, especially in the afternoon and evening on Mt. Hood.  

Watch for recent wind slab formed Saturday afternoon through Sunday on lee easterly aspects. Fresh wind slab should be found near and above treeline. Be aware that the winds above treeline are forecast to increase Monday afternoon and should continue loading the same lee easterly aspects during the latter part of the day.

Watch for loose dry avalanches on steeper slopes in non-wind affected terrain. Be especially wary of fast running loose dry avalanches near terrain traps. 

Storm slabs will not be listed as an avalanche problem but watch if recent storm storm forms a cohesive slab above weaker snow in specific areas on Monday. 

Give cornices a wide berth when traveling along ridgelines and avoid lingering on slopes below cornices as they may fail at any time.

Snowpack Discussion

Weather and Snowpack

The most recent atmospheric river arrived on Valentines Day 2/14 and formed the uppermost significant rain crust in our snowpack. 

About 2 feet of snow accumulated at the NWAC Mt Hood stations from Sunday 2/19 through Wednesday 2/22. 

Saturday began mostly sunny but high clouds increased in the afternoon. Light snow showers on Sunday deposited about 4-6 inches of low density snow with light to moderate transport winds out of the west near and above treeline.    

Recent Observations

A widespread loose dry avalanche cycle was observed by the Meadows pro-patrol in steep terrain up to 8000 feet on Saturday. 

On Sunday, Meadows pro-patrol reported pockets of fresh 12-18" wind slab on NE and E aspects near and above treeline that were easily ski triggered but not running far during avalanche control work. 

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.

Loose Dry

Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.