Avalanche Forecast
Issued: Feb 1st, 2016 10:35AM
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
The greatest avalanche problem should be wind slab on lee slopes near and above treeline mainly N-SE facing slopes. Watch for signs of cracking or firmer wind transported snow.
Summary
Detailed Forecast
One more day of light winds, few if any light snow showers and cool temperatures should be seen along the west slopes on Tuesday.
This weather should bring a further gradually decreasing avalanche danger.
The greatest avalanche problem should be wind slab on lee slopes near and above treeline mainly N-SE facing slopes. Watch for signs of cracking or firmer wind transported snow.
Also watch for lingering storm slab in areas that had rapidly accumulating snowfall.
Although this won't be listed as a problem watch for triggered loose dry avalanches if you venture onto very steep slopes.
The weather should stay cool tomorrow but the amount of overall cloud cover is a bit hard to determine. Loose wet avalanches also won't be listed as a problem but if solar effects or sun are significant watch for wet snow deeper than a few inches and pinwheels or small natural loose wet avalanches that usually precede larger loose wet avalanches on solar slopes.
Avoid ridges where cornices may be present and slopes below cornices. Cornices can always be sensitive to human triggers.
Continue to evaluate snow and terrain carefully on Tuesday.
Snowpack Discussion
Weather and Snowpack
Two fair weather periods earlier this month allowed surface hoar and near surface faceting to occur. These persistent weak layers were buried intact on January 3rd and 11th throughout the Cascades.
Two heavy rain events, one about January 21st and one last Wednesday-Thursday are expected to have eliminated the January persistent weak layers and formed crusts in the upper snowpack in the west slope zones.
A strong occluded front with strong winds crossed the Northwest on Friday. NWAC stations along the west slopes had about 1-1.5 feet of new snow by Saturday morning. Some further light amounts of snow except for about 7 inches at Mt Baker followed at the tail end by Sunday morning. Cool weather with some light snow showers has been seen along the west slopes Sunday and Monday. This storm snow has accumulated on the crust from last Wednesday-Thursday.
Some areas have reported a strong bond of the new snow to the crust and some a poor bond depending on if the new snow arrived after cooling began. Sensitive storm layers have also been reported within the storm snow which will take a bit of time to gradually stabilize.
Recent Observations
Decreasing avalanche activity was reported over the weekend. Here are summaries of some of the latest reports.
Three NWAC pro-observers visited the Stevens Pass and Paradise areas on Sunday and generally reported possible wind slab on previous lee slopes and possible storm slab in storm snow in the near and above treeline as the main avalanche problems.
A ski triggered 25 cm x 30 m wide storm slab in the northwest zone near tree line on a convex slope was reported via the NWAC Observations page for Sunday. A specific location was not given.
NWAC pro-observer Lee Lazzara was in the Mt Baker area on Monday and reported small wind slab varying in depth from 20-40 cm over slightly lower density snow but lacking clean shears. Skiers were also triggering loose dry avalanches on steep 45 degree slopes.
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
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 2nd, 2016 10:35AM
