Avalanche Forecast
Issued: Feb 9th, 2015 10:22PM
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
A transition from the recent wet warm weather to dry warm weather will begin on Tuesday. You will need to watch for a variety of snow and avalanche conditions on Tuesday.
Summary
Detailed Forecast
The upper ridge will begin to rebuild over the west US on Tuesday. This should cause light west winds with light showers mainly west of the crest decreasing Tuesday morning and ending Tuesday afternoon.
Wind slab from the past couple days may linger mainly on steep N to SE slopes near and above treeline. Watch for firmer wind transported snow.
New storm slab seems unlikely and would be mainly in the south part from Monday where there is more than a few inches of snowfall in areas with light wind. This problem should be limited if any due to limited new snow east of the crest and the brief cooling trend.
Any cooling will be limited Tuesday morning and temperatures will be on the rise again by Tuesday afternoon. More mostly small loose wet avalanches may be seen again below treeline Tuesday afternoon on steep mainly solar slopes.This will not be listed as an avalanche problem east of the crest. But reconsider this if you seen more than a few inches of wet snow or natural loose wet avalanches on solar slopes.
As a result of the unseasonably low snowpack, especially at lower elevations, watch for terrain hazards such as open creeks, partially covered rocks and vegetation.
Snowpack Discussion
A series of fronts in an atmospheric river has been crossing the Northwest from about February 5th-10th. The east slopes have seen quite a variety of weather and snow conditions. The Harts Pass Snotel and the NWAC Washington Pass weather stations total snow gages indicate about a foot of snow during this period. Other areas east of the crest have had less snow or rain.
NWAC pro-observer Jeff Ward was in the Stuart Range Friday and at 6500 feet found touchy small loose wet avalanches. Below this elevation there was not enough new snow for wet loose danger and older snow was consolidated with little concern for loose wet avalanches.
NWAC pro-observer Tom Curtis was at Dirty Face Peak on Saturday and found small roller balls in recent snow with no recent avalanches and no signs of instability.
The North Cascades Mountain Guides were at Washington Pass on Sunday and found 30-40 cm of storm snow with touchy 6 inch storm slab above 7000 feet. They also reported lots of small loose wet avalanches at lower elevations. Larry Goldie sent a photo of a crown below cliffs near Silver Star from during the February 5th-10th storm cycle.
NWAC pro-observers and North Cascade Guide reports last week in the northeast and central east zones have the January 15th facet/crust layers at 35 cm-1 m below the surface with the facets starting to turn to rounded grains and not reactive or not releasing in pit tests. So it appears the January 15th facet/crust layers are strengthening and stabilizing. This problem has been removed from the central east zone forecast but retained in the northeast zone until more information becomes available there.
A filling low pressure system is crossing mainly the south Cascades on Monday. This is causing the most wind and rain or snow in the south Cascades on Monday. Lighter west winds and mostly light rain or snow showers mainlywest of the crest will follow Monday night. A brief minor drop in snow levels should be seen mainly in the south Cascades Tuesday morning.
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.
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: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Feb 10th, 2015 10:22PM
