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RegisterJan 25th, 2018–Jan 26th, 2018
Snoqualmie Pass.
Dangerous avalanche conditions will persist on Friday due to additional light snowfall, an uptick in wind transported snow, and cold temperatures preserving recent storm instabilities. Avoid steep open slopes connected to large avalanche paths until we exit this storm cycle. Give safe margins near and below growing cornices. Tree-well and snow immersion hazards are very dangerous, so keep communication with your partner at all times.
Dangerous avalanche conditions will persist on Friday due to additional light snowfall, an uptick in wind transported snow near and below ridges, and cold temperatures preserving recent storm instabilities. Due to lower density surface snow available for transport and moderate W-SW winds forecast, wind slabs may develop below treeline or further downslope than you might expect Friday. Avoid travel on slopes if you encounter wind stiffened surface snow, especially on steeper exposed terrain and steep roll-overs.
The potential for large and destructive avalanches remains in bigger terrain. Avoid travel on or below slopes connected to large avalanche paths until we exit this storm cycle. Give safe margins near and below growing cornices. There's plenty of good snow out there, so maintain a conservative approach to terrain selection.
Significantly transformed snow conditions have taken place during this extended storm cycle. Tree-well and snow immersion hazards are very dangerous, so keep communication with your partner at all times.
An extended storm cycle continues. Over the past 8 days, 2.5 to 5 ft of storm snow has fallen over a strong rain crust buried 1/16. Mt Baker has been the exception with roughly 9 ft of storm snow received in the past week! Cool and generally light showers were seen on Thursday with light to moderate winds transporting snow near and below ridgelines from Snoqualmie Pass and southward. Recent storm snow instabilities were healing, but a large skier triggered slab avalanche was reported in the closed Alpental ski area Thursday.
Warming early Wednesday along with heavy snowfall and strong winds led to a natural avalanche cycle in some areas. Slab avalanches of 1-2 ft were common.
Poor visibility and frequent storm conditions have limited observations above treeline during this period.
Observations
Central
On Thursday morning, NWAC staff in the Alpental valley observed debris from a large to very large natural avalanche that released from Chair Peak and ran down to Source Lake. The avalanche most likely occurred within the previous 24 hours. Professionals at the closed Alpental ski area reported a large skier triggered slab avalanche 20" deep releasing in the Powder Bowl area. Fresh large cornices have built along ridgelines in this area.
On Wednesday, NWAC professional observer Jeff Ward traveled in wind sheltered terrain below treeline, just east of Stevens Pass, finding 2-2.5 ft of storm snow. In this terrain with little to no wind effect, the storm snow had a favorable density profile of gradually increasing density with depth. No reactivity was found in tests within the gradually settling storm snow.
On Wednesday, NWAC Pro observer Ian Nicholson traveled in the Kendall Trees near Snoqualmie Pass. Warming early Wednesday formed sensitive storm slabs with several natural storm slabs releasing about 12-16" on a storm density change (see instagram post).
South
NWAC forecasters in the Crystal backcountry on Thursday reported 1 to 2 feet of recent storm snow well bonded to the 1/16 crust. The new snow generally had a right-side up profile with recent storm instabilities healing, with the exception of areas of poor bonding noted on windward slopes with a shallower snowpack. Occasional gusty winds transported recent snow in the Crystal area near and below ridges but wind slab was found to be generally unreactive in the areas observed.