Avalanche Forecast
Regions: Cascades - South East.
Saturday's avalanche forecast will depend on the storm overnight. Heavy snow and strong winds will create dangerous avalanche conditions above treeline. Below treeline, slowly refreezing wet snow and shallow new snow will create a significantly lower danger. Local conditions may vary greatly, so be prepared to adjust plans accordingly.
Detailed Forecast
A low pressure system is tracking towards the central Washington coast from the SW, expected to move inland across the Olympics Friday night. This system should spread increasing precipitation, strong winds and rising snow levels, late Friday through early Saturday. The peak in winds, snow levels and precipitation are expected Friday night into early Saturday morning. Significant cooling, diminishing showers and winds are expected through the day Saturday.
Along the Cascade east slopes previous wind slab is most likely to linger on NW to SE aspects due to previous SW-W winds. But watch for firmer wind transported snow on other aspects, especially in areas of complex terrain.
The biggest factor affecting Saturday's avalanche forecast confidence will be how much precipitation is received overnight and to what elevation the rain/snow line reached.
New wind slabs are likely to have built on NW to SE aspects, mainly above treeline. But watch for firmer wind transported snow on other aspects, especially in areas of complex terrain.
At lower elevations, rain Friday night should leave a wet and slowly re-freezing snowpack with shallow new snow accumulation expected Saturday. Small loose wet avalanche conditions are most likely to persist at lower elevations, especially if the cooling is delayed early Saturday. Watch for surface wet snow deeper than a few inches, rollerballs or increasing small natural releases.
Although the likelihood of wet slab or glides avalanches has greatly decreased with the recent re-freeze, these avalanche problems may reemerge following the warm and wet weather Friday night. Continue to avoid unsupported slopes where you know there is a smooth underlying surface, or slopes with glide cracks.
It is always a good plan to travel well back from ridges, suspected of cornice formation, or on steep slopes below cornices.
Remember to re-evaluate or change plans if local conditions vary from forecast conditions.
Snowpack Discussion
Weather and Snowpack
The first week or so of March was very cool and snowy. NWAC and NRCS stations indicate about 2 feet of snow in the northeast Cascades with less elsewhere along the Cascade east slopes.Â
A strong frontal system brought increasing precipitation, winds and warming to the Cascades on Thursday 3/9. On Thursday night rain may have pushed up to about 4000 feet in the northeast Cascades and about 5000 feet in the southeast Cascades. By Friday morning 3/10 NWAC stations along the Cascade east slopes had about 0.35- 0.90 inches of WE (water equivalent) with only 0-5 inches of snow.
Moist W-SW flow and a stalled frontal boundary have produced periods of light to moderate rain and snow along the east slopes of the Cascades Monday through Wednesday. There was a strong downslope drying effect with much less precipitation east of the crest during this time. Precipitation amounts ranged from less than 0.5 inches to about 1.5 inches of water equivalent over the three days.  Snow levels pushed above 6500 feet Tuesday afternoon with the summit stations at Mission Ridge, Washington Pass, Harts Pass and Dirty Face Peak all above freezing. About 1-2 ft of snowpack consolidation was seen in the central east and southeast Cascades with  more snowfall and less consolidation in the northeast Cascades.
Cooling and light amounts of new snow were seen east of the crest Wednesday night.
Recent Observations
North
NCMG Larry Goldie went as far as the Cutthroat trailhead on Wednesday 3/15 and saw or heard numerous natural loose wet and wet slab avalanches possibly to size 2.5 so the natural avalanche cycle was continuing there.
The North Cascades Heli Guides were near Silver Star on Thursday 3/16 reported many previous natural storm slab avalanches up to size 3, likely releasing midweek. They also reported several small triggered storm slab avalanches. This activity was on N-NW slopes in the 8000 ft range.
More observations from Friday in this zone, indicated a significant distinction in the recent storm snow with elevation, with up to 4 more inches of storm snow above about 6500 feet. The several recent warm precipitation events this week appear to have limited the upper elevations of rain to about 6500 feet. At elevations up to 8000 feet, the recent precipitation has fallen as snow. In these higher elevations, some shallow triggered storm slab avalanches have been noted over the past few days.
Central
NWAC observer Jeff Ward was in the Cle Elum drainage on Mt Hawkins and Red Mountain up to about 6000 ft on Thursday 3/16 and noted evidence of an impressive avalanche cycle the past couple days. The current conditions were 3 cm of new snow over 3-7 cm thick, firm crust with recent rain penetration to about 40 cm in the snowpack. The Valentine's Day crust was found at 90 cm but tests did not give results.
NWAC observer Tom Curtis was at Blewett on Diamond Head up to about 5500 ft on on Thursday 3/16 where there were no recent avalanches just consolidation. SW-W-NW slopes were scoured, with a breakable or supportive crust elsewhere over moist 1F or P rounded crystals down to the ground. He found some reactivity in a layer at about 50 cm down, which should not be a current problem, but might have contributed to avalanches a week ago.
South
No recent observations.Â
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, North West.
Elevations: Alpine, Treeline.
Likelihood: Likely
Expected Size: 1 - 1
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.
Elevations: Below Treeline.
Likelihood: Possible
Expected Size: 1 - 1