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RegisterMar 17th, 2017–Mar 18th, 2017
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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.
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.
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.
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.