Confidence : Medium. Distribution: SW-S-SE aspects, and cross loaded terrain on other aspects.
The weather section (below) says it all: in the last 10 days we formed a heavy rain crust (the MLK crust), with 1-2ft of snow above it, then a surface hoar layer formed, followed by 4″ of new snow, followed by a strong NE to NW wind event Jan 25-27.
Those NE-NW winds caused heavy wind loading on lee aspects, and built alpine wind slabs in starting zones, gullies, and terrain features. These slabs will have high variability in the alpine. Human-triggering is possible, especially in wind-protected pockets where buried surface hoar is most likely, and on slopes 35-degrees and steeper. Pole probing will help you identify and avoid slabby or hollow-feeling areas where there is a wind slab over softer snow. Test slopes will be helpful, but expect each slope to be different. Wind slabs will likely run on/above the MLK rain crust, which sits about 30cm deep in the alpine.
Confidence: Low. Distribution: Isolated to Widespread. We have two deep persistent weak layers:
We have not seen these persistent layers to be active in the last week, but heavy triggers like cornice fall, snowmachine drops, and step-downs could possibly trigger these deep layers. These weak layers are tricky and could produce large, deadly avalanches, especially in steep terrain, rollovers, and wind loaded areas. If an avalanche were to break this large, expect very wide propagation, where safe zones can easily be entrained in a slab. Be especially careful about trusting your safe zones.
(Surface hoar near-treeline in the Transitional Zone 12/31. Once buried by wind slab or new snow these feathery crystals become a dangerous persistent weak layer that will require extremely careful assessment and overall immediate avoidance in avalanche terrain. Photo: Tim Thomas)
We had a natural avalanche cycle on Jan 17th-18th, when temperatures warmed and rain fell up to 3000ft. A wet slide crossed the Haines highway at 21-mile, and other paths in the backcountry ran as well. Later on the 18th, temperatures dropped and 18-24″ of snow fell down to 2000ft. A smaller cycle ran within this new snow above the MLK-day rain crust. Most slides were 30-60cm deep (D2.5), but at least three slides ran deeper (perhaps down to the New Year’s Surface hoar layer 1.5m deep) with wider propagation (D3, N aspect). These deeper slides appear to been caused by cornice failures/heavy triggers.
A heavy rain crust formed Jan. 18th up to 3000ft, and then 1-2ft of snow fell on top. Surface hoar formed Jan 21-22, followed by 4″ of new snow on Jan. 23rd. Since then we had a strong NE to NW wind event Jan 25-27. The Mt. Ripinsky weather station is completely buried and no longer reporting snow depth.
( *star means meteorological estimate )
There are two more avalanche problems to be aware of today: Dry-Loose sluffs that can knock you into dangerous situations in steep terrain, and Falling Cornice. Expect a fast sluff in steep terrain, and give any cornices a wider berth than you think they need.
Practice like you play. Dust off your gear and make sure it is fully functional. Put new batteries in your beacons! Make sure everyone in the group has a functioning beacon, shovel and probe – and knows how to use them, keep your skills fresh. If you head into the hills, watch out for red flag avalanche conditions, natural avalanches, whumphing or collapsing, and shooting cracks.
Education Video Links:
Click the + Full Forecast link below for each zone to read more. Submit observations. Win prizes. Each snow, weather & avalanche observation will be entered in a raffle drawing. Submit confidential reports and findings to [email protected]
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