Avalanche Forecast
Issued: Mar 30th, 2015 12:39PM
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
Moderate danger mainly applies closer to the Cascade crest and lower avalanche danger is expected further away from the Cascade crest Tuesday. Increasingly sensitive avalanche conditions involving shallow amounts of new snow are possible on lee slopes near and above treeline as well as loose wet avalanche concerns during sunbreaks and daytime warming Tuesday afternoon.
Summary
Detailed Forecast
A frontal system passing through late Monday night should be followed by orographic showers and a cooling trend Tuesday. Showers may be locally intense near the Cascade crest Tuesday afternoon with more moderate snowfall accumulations possible for the east slopes downwind of a Puget Sound convergence zone between Stevens and Snoqualmie Passes.
Moderate danger mainly applies closer to the Cascade crest and lower avalanche danger is expected further away from the Cascade crest Tuesday. Increasingly sensitive avalanche conditions involving shallow amounts of new snow are possible on lee slopes near and above treeline as well as loose wet avalanche concerns during sunbreaks and daytime warming Tuesday afternoon.
Cornices won't be listed as an avalanche problem but be aware of new cornice growth along ridgelines.
Many areas at lower elevations and further away from the Cascade crest do not have enough snow to cause an avalanche danger.
Snowpack Discussion
The 1-2 feet of snow that fell in mid-March east of the crest, mainly in the northeast Cascades, has settled into the upper snowpack.
A warm front caused only light amounts of rain and snow east of the crest Wednesday to Thursday morning with gradual warming along the east slopes. NWAC Observer Tom Curtis was on Nason Ridge on Thursday and reported small to medium rollerballs and evidence of recent small to large loose wet avalanches.
A front and short wave crossed the Northwest Friday night causing strong west-southwest winds, some rain and snow and lowering snow levels. But rain and snow amounts were light east of the crest.
During the mild and fair weather Monday, avalanche professionals working in the Washington Pass area caused significant slides Monday using explosives. Wet slab avalanches entrained moist snow in the with Liberty Bell paths and buried the closed highway with several feet of debris. One size-able wet loose avalanche was observed off of Kanagroo Ridge as well Monday.
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.
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: Mar 31st, 2015 12:39PM
