Avalanche Forecast
Issued: Apr 4th, 2015 11:00AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Loose Wet.
NWAC,
Northwest Avalanche Center
Generally good stability is expected Sunday, but evaluate lee slopes near and especially above treeline for local wind slab and be aware of small loose avalanches that could be problematic near terrain traps.
Summary
Detailed Forecast
Another day of weak flow aloft and cool snow levels with mainly afternoon/evening shower activity is expected Sunday. New snow amounts are expected to be light Saturday night and Sunday.
There haven't been many reports of wind slab, but isolated pockets of wind slab may linger on traditional lee westerly aspects from recent storms near and above treeline.
It's April, so be aware of increased solar input reaching more aspects and affecting the snow surface more quickly than winter-time. Loose wet avalanches involving recent storm snow will be possible Sunday. Varying amounts of cloud cover Sunday will make the regional loose wet likelihood hard to pin down.
Small loose dry avalanches are also possible on non-solar aspects. Loose dry avalanches won't be listed as a top avalanche problem, but be aware of fast moving sluffs knocking you off your feet and into unintended terrain traps on steeper slopes.
Due to the continued cool weather, cornices won't be listed as an avalanche problem either but use caution on slopes below cornices and on ridges where it can be hard to know if a cornice is present.
Snowpack Discussion
The recent active weather since about mid March onward has brought periodic light snowfalls east of the crest and allowed general snowpack consolidation and stabilization.
During the fair and mild weather Monday Mar 30th, DOT avalanche professionals working in the Washington Pass area triggered slides using explosives. Wet slab avalanches entrained moist snow in the Liberty Bell paths and buried the closed highway with about 8 ft of debris. Little natural avalanche activity was observed in the area during this time period.
A front moved across the Northwest Tuesday followed by showers and rapid cooling but caused little snow east of the crest expect locally downwind of a convergence zone centered on Snoqualmie Pass.
A TAY report from Mt. Stuart Thursday reported 6-12" of unconsolidated snow even on solar aspects above treeline, likely a benefactor of Tuesday night's convergence zone. NWAC observer Jeremy Allyn was at Washington Pass on Friday and found about an inch of recent snow on a thick crust that needed additional loading to become problematic, however about an inch or less fell Friday night along the east slopes.
Snowdepths vary greatly across the east slopes with a regionally healthy snowpack in the northeast Cascades to bare solar and lower elevation slopes in the central and southeast Cascades. Many areas at lower elevations and further away from the Cascade crest do not have enough snow to cause an avalanche danger.
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
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: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Apr 5th, 2015 11:00AM
