Avalanche Forecast
Regions: Cascades - South East.
The stability of the Cascades snowpack has greatly increased after avalanche cycles and consolidation the past week. You should mainly need to watch for previous slab at higher elevations and the development of loose wet avalanches at lower elevations on Friday.
Detailed Forecast
A low pressure system is expected to form well to the SW of track towards the central Washington coast on Friday, before moving inland Friday night. This system should spread increasing light precipitation to Mt Hood Friday morning, before spreading to the remainder of the forecast area Friday afternoon, with rising snow levels. The peak in winds, snow levels and precipitation are expected Friday night into early Saturday morning.
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.
Small loose wet avalanche conditions are most likely to linger at lower elevations or to develop as rain moves in on Friday afternoon. Watch for surface wet snow deeper than a few inches, rollerballs or increasing small natural releases.
It is always a good plan to avoid areas on ridge where a cornice maybe present and slopes below cornices.
Remember to re-evaluate plans if weather conditions are different or deteriorate sooner than expected.
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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 past 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.
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. They also reported several small triggered storm slab avalanches. This activity was on N-NW slopes in the 8000 ft range.
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 has 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.
Likelihood: Possible
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: Treeline, Below Treeline.
Likelihood: Possible
Expected Size: 1 - 1