Avalanche Forecast
Issued: Mar 27th, 2016 11:00AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Loose Wet, Wind Slabs and Storm Slabs.
NWAC,
Northwest Avalanche Center
A mix of dangerous winter and spring avalanche conditions is likely to linger in all 3 elevation bands along the west slopes following weather and snowfall on Sunday.Your ability to identify and avoid avalanche problems will be essential on Monday.
Summary
Detailed Forecast
An upper ridge and surface high pressure should begin to strongly build west of the US west all the way to the Gulf of Alaska on Monday. Light snow showers on both sides of the crest should decrease and end on Monday. New snow along the west slopes from Sunday should be mostly in the 5-10 inch range above about 4-5000 feet by Monday morning.
A mix of likely dangerous winter and spring avalanche conditions is likely persist along the west slopes on Monday. The sun is getting much stronger and new snow will be reactive to solar effects.
Loose wet avalanches should be likely especially on solar slopes on Monday. Avoid avalanche terrain if you start seeing pinwheels or initial small natural loose wet avalanches. Be aware of terrain traps where even a small loose wet avalanche could have unintended consequences.
New wind slab of a foot or more is likely on lee slopes mainly in the near and above treeline on Monday. This is most likely on north to east slopes but possible on other aspects. Watch cracking and firmer or chalky wind transported snow. Remember that snow pits may not be helpful due to variability in the snowpack.
New storm slab layers may linger into Monday where there was rapidly accumulating snow for more than a few hours on Sunday. Pay special attention to slope convexities where storm slab is mostly likely to be triggered.
Cornices have grown large recently. Cornices can break much further back on ridges than expected and releases can be unpredictable during the spring.
Although not listed as an avalanche problem, large powerful glide avalanches can release unexpectedly so avoid areas below steep unsupported slopes or rock faces.
Snowpack Discussion
Weather and Snowpack
Snow accumulations Wednesday to Friday following the last front varied based on elevation, with only a few inches below 4000 feet and 6-21 inches above. The most snow was received at the NWAC Baker and Paradise stations. This snow was generally well-bonded to a moist crust buried March 22nd.
A strong front and upper short wave crossed the Northwest Sunday morning. This is being followed by a large upper trough and cool unstable air mass Sunday afternoon and evening. Convergence Sunday afternoon has already shifted to near Snoqualmie.
Frequent March storms have built large cornices along ridges in many areas.
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
On Friday the Baker pro-patrol reported natural slab activity above treeline on Mt. Shuskan but only small loose wet releases in area and a generally right side up upper snowpack.
NWAC pro-observer Lee Lazzara was out near Mt Baker on Friday and generally found 50 cm of storm snow on a rain crust from 3/21. He saw numerous loose wet avalanches on various aspects and despite warm temperatures some ski triggered loose dry avalanches were still seen on steep north slopes.
A professional guide observation from the Snoqualmie Pass area Friday morning indicated generally well layered and bonded storm snow with increasing potential for loose wet avalanches by late morning.
Further south Dallas Glass was out again near Paradise on Friday and found 60 cm of settled, bonded storm snow. He witnessed large rollerballs to 3 feet in diameter - watch out for those! Several small natural and ski triggered loose wet avalanches were seen on east to south facing slopes. There was significant wind redistribution of snow in the above and near treeline wind possible wind slab to 15 inches deep on north to southeast slopes.
Problems
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: East, South East, South, South West, West.
Elevations: All elevations.
Likelihood
Expected Size
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: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Mar 28th, 2016 11:00AM
