Avalanche Forecast
Regions: Cascades - East.
Mostly small, shallow areas of new wind and storm slab will be possible in the near and above treeline on Saturday. Avalanche problems would be greater if there is more new snow than expected.
Detailed Forecast
Rain or snow should change to showers Friday night with lower snow levels. Some sun should be seen along the east slopes by Saturday afternoon.
This weather should bring light amounts of snow mainly near and above treeline along the east slopes with a cooling trend. The cooling trend with rain changing to snow mainly in the near and above treeline should help bond new snow to previous snow.
New small areas of mostly shallow wind slab will be possible on isolated lee slopes. This should be mainly N to E slopes near and above treeline. Watch for firmer wind transported snow.
Small areas of shallow storm slab will also be possible if any areas receive a few inches of rapidly accumulating snowfall.
These avalanche problems would be greater if there is more new snow than expected.
Snowpack Discussion
Weather and Snowpack
Dry weather with the warmest temperatures of the winter occurred February 7-10th with temperatures climbing into the 50's in most areas east of the crest.
Snow in the northeast zone buried the crust with about 1.5-3 feet of snowfall February 11-20th.
Rain and mild temperatures were seen in the central east and southeast zones in mid February forming a newer crust in those areas. An active and cooler pattern buried the crust in the central and southeast zones with about 6-10 inches of snow in the near and above treeline February 17-20th.
Up to a few inches of additional snowfall fell east of the crest by Monday morning. Moderate E-SE crest level winds in places east of the crest Monday night and Tuesday may have redistributed surface snow to unusual west slopes in some places east of the crest.
Sun and very mild temperatures were seen Wednesday and Thursday rising into the 40's or 50's. This fair and mild weather will have wet surface snow and night time melt form crust formation and helped to stabilize earlier wind slabs.
Increasing clouds Friday should have helped limit solar effects in some or most areas east of the crest.
Recent Observations
NWAC pro-observer Tom Curtis was in the Chiwawa River drainage on Wednesday and saw loose wet avalanches on most aspects and elevations. Signs of wind slab were seen on northwest to southeast slopes near and above treeline.
Tom was out again at Blewett Pass on Thursday and found cool wind transported snow on lee slopes near tree line that was not cohesive or reactive.
NWAC pro-observer Jeff Ward was out near Washington Pass on Thursday and found powder and good ski conditions on north to east slopes. Several loose wet avalanches up to size 1-2Â were seen on on steep solar terrain. Surface hoar up to 15 mm was also seen on non-solar slopes. A large cornice release was seen in the Cutthroat Creek drainage.
The North Cascade Mountain Guides near Washington Pass on Thursday also found powder snow on non-solar slopes, surface hoar in the valley bottom and noted loose wet avalanches on solar slopes up to size 1-1.5.
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Avalanche 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, West, North West.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 1
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: Possible
Expected Size: 1 - 1