Avalanche Forecast
Issued: Feb 13th, 2018 10:25AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Storm Slabs.
NWAC,
Northwest Avalanche Center
Avalanche conditions will begin to change Wednesday as moderate westerly winds transport new snowfall and quickly build fresh wind slabs on lee slopes near and above treeline. Avoid steep slopes with wind deposited snow such as below cornices, on wind drifts, and near uneven snow surfaces. Shallow storm slabs may develop in less wind affected areas throughout the terrain Wednesday.
Summary
Detailed Forecast
A quick moving frontal system should bring fresh snowfall to Mt. Hood late Tuesday night and Wednesday morning along with much cooler temperatures. 6-12 inches of new snow may bond poorly to a medley of wind sculpted snow surfaces or surface crusts.
Avalanche conditions will begin to change Wednesday as moderate westerly winds transport new snowfall and quickly build fresh wind slabs on lee slopes near and above treeline. Avoid steep slopes with wind deposited snow such as below cornices, on wind drifts, and near uneven snow surfaces. Shallow storm slabs may develop in less wind affected areas throughout the terrain Wednesday. Watch for developing storm slab instabilities during extended periods of intense snowfall.
Loose dry avalanches will not be listed as a problem but will be possible on very steep slopes. Be aware of the consequences of a loose dry avalanche near terrain traps such as cliffs, gullies, or open creeks. In areas where shallow loose new snow bonds poorly to the underlying crust, avoid steep icy slopes where it will be difficult to stop a fall.
Snowpack Discussion
Temperatures pushed into the upper 30s and 40s under mostly sunny skies Tuesday. Westerly winds near and above treeline picked up late in the day. Softened snow surfaces will quickly refreeze due to winds and cooling temperatures Tuesday night.
Warm and wet weather the first week of February created a strong and consolidated snowpack. The current snowpack consist of numerous old crusts and very strong refrozen layers. There are no significant layers of concern at this time.
No avalanches have been observed over the last several days.
Observations
Mt Hood Meadows ski patrol Sunday reported very firm surface snow conditions resulting in no current avalanche problems.
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, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Storm Slabs
Release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. 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.
You can reduce your risk from Storm Slabs by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.
Storm slabs usually stabilize within a few days, and release at or below the trigger point. They exist throughout the terrain, and can be avoided by waiting for the storm snow to stabilize.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Feb 14th, 2018 10:25AM
