Avalanche Forecast
Issued: Mar 14th, 2016 11:49AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs, Storm Slabs and Loose Wet.
NWAC,
Northwest Avalanche Center
Conservative decision making will be essential Tuesday as recent storm and wind slabs will require additional time to settle and stabilize. Avoid steep open slopes showing signs of recent wind transport. Best to confine travel to lower angled terrain away from wind effects.
Summary
Detailed Forecast
Additional showers are expected Tuesday at continued cool temperatures. Showers should generally be fewer and taper by late Tuesday.
Moderate west winds at ridge level should persist Tuesday before diminishing late Tuesday.
Recent or new wind and storm slabs will remain the main avalanche problems Tuesday along the west slope zones.
New wind slab is mostly likely to be found on NW-SE facing slopes. Stiff wind transported snow and snowpack cracking can be good signs of wind slab or storm slab instabilities.
New storm slab is likely in areas where new snow rapidly accumulates for more than several hours.
Cloudy cool conditions Tuesday may limit the possibility of loose wet snow but the sun is gaining power so watch for the possibility of loose wet snow on solar slopes if extended sun breaks occur.
The avalanche danger should gradually decrease Tuesday with less wind and slow settlement and stabilization of new snow and fairly cool temperatures.
Snowpack Discussion
Weather and Snowpack
Storms have moved across the Northwest at a nearly daily frequency the past few weeks with fluctuating but generally moderate snow levels.
A storm last Wednesday and Thursday caused a warming trend that peaked Wednesday night with very strong west winds throughout the Cascade range. About 4-14 inches of snow accumulated on a new crust in most areas along the west slopes byThursday morning. Additional accumulations were light Thursday except above 5000 feet in the Mt. Baker area where another foot of snow likely fell.
A front on Saturday caused W-SW winds and another 1-10 inches of snow ending Sunday morning with the most at Mt Baker, Crystal, and Paradise.
A deep surface low-pressure system moved across the Olympic Peninsula Sunday causing very stormy weather across the region.
Cool showery weather Monday with continued moderate westerly winds continues to deposit additional snow at lower temperatures.
New storm amounts along the west slope sites range from about 10-25 inches deposited in the past 36 hours as of Monday evening.
Strong winds and recent storms have created widespread wind and storm slab problems, creating dangerous avalanche conditions.
The mid and lower snowpack along the west slopes should generally be a stable mix of crusts and layers of moist and rounded snow crystals.
Recent Observations
A park ranger early Monday morning 3/14, assessing avalanche conditions for plow drivers to Paradise, found sensitive storm slabs with cracks extending from ski tips and one slab releasing remotely. 24 hr storm snow was 15 inches and recent storm snow 30 inches down to the crust formed after rain Tuesday night, 3/9.
Storm slab sensitivity Monday morning 3/14, near Paradise, Mt Rainier, near tree line. Photos: NPS Peter Ellis
NWAC observer Dallas Glass in the Crystal Mountain backcountry Monday 3/14, found surprisingly good stability within the deep storm snow. However, these observations were limited to below tree line and were confined to slopes less affected by recent strong winds. In general, 24 hr new snow depths were 10-12", with previous storm totals of about 2 feet down to the 3/9 rain crust. Storm snow exhibited a favorable density profile. A cornice dropped onto a north facing slope produced no avalanche on slope below.
NWAC ambassador Jeff Hambleton was near Mt Baker on Sunday and reported a 3-foot natural slab avalanche on a north facing slope at about 6000 feet on Mazama Peak. He also reported there were several ski triggered slab avalanches on the north side of Shuksan Arm which would be in the 4500-5000 foot range but details are lacking.
The Crystal pro-patrol on Sunday reported mostly small but widespread ski triggered 4-12 inch wind slabs on north to west slopes near the ridges due to strong southeast winds. A private party via email also reported sensitive wind slab of 6-12 inches on varied aspects at Crystal Mountain on Sunday.
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
Loose Wet
Release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.
Several loose wet avalanches, and lots of pinwheels and roller balls.
Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.
Aspects: South East, South, South West.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Mar 15th, 2016 11:49AM
