Avalanche Forecast
Regions: Cascades - West.
The cool somewhat snowy weather should bring a variety of changeable March snow and avalanche conditions.
Detailed Forecast
Light snow showers should continue over the west slopes Tuesday with weak convergence Stevens to Snoqualmie and fairly low snow levels.
The cool somewhat snowy weather should bring a variety of changeable March snow and avalanche conditions.
We are past the equinox and the sun is rapidly getting stronger and new snow will be susceptible to sun effects. Watch for wet snow deeper than a few inches or snowballing or natural loose wet avalanches by Tuesday midday on solar slopes.
Previous wind slab may linger on lee slopes mainly ATL or NTL. Use extra caution near slope convexities where storm or wind slab avalanches are more likely to be triggered.
In most of the Washington Cascades by Tuesday new snowfall should not be great and storm slab will not be listed as an avalanche problem. But watch for storm slab if you encounter new snow deeper than several inches.
Remember the NWAC forecast applies to elevations up to the Cascade crest. A greater danger is often found above the crest on the upper volcanoes.
Less recent snow and ample terrain anchors should limit the avalanche danger below treeline. Many areas below treeline do not have enough snow to cause an avalanche danger.
Snowpack Discussion
The storm late last week and over the weekend caused strong winds and heavy snow mainly ATL in the Mt Baker area. At the NWAC station at the base of the Mt Baker Ski Area there was about 8 inches of snowfall and there was up to a few inches elsewhere along the west slopes.
NWAC observer Jeremy Allyn was in Silver Basin on Saturday and found sensitive cornices and triggered storm and wind slab of 4-6 inches.
Near the Mt Baker Ski Area on Sunday NWAC observer Jeff Hambelton reported small loose wet avalanches on the north slopes of Table Mountain. No slab releases were seen with the new snow feeling moist, settled and mostly stable. But higher on Heliotrope Ridge a skier triggered and was partly buried by 1-1.5 foot storm or wind slab avalanche.
NWAC observer Dallas Glass was at Paradise on Sunday and also reported possible loose wet avalanche conditions NTL and ATL without evidence of storm or wind slab.Â
The mid and lower snowpack west of the crest consists of layers of stable consolidated rounded grains or melt forms and crusts from multiple warm periods this winter.
A weak upper short wave and unstable air mass is moving over the Northwest on Monday. This should slightly favor the volcanoes for snow showers. Another rapidly moving shortwave will carry a surface low across the north Oregon Cascades Monday night. This should renew snow showers Monday night in the south Cascades with possible overnight stormy conditions at Mt Hood.
Avalanche 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: South East, South, South West.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 1
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, North West.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 1