|Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
|Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
|Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding, and conservative decision-making essential.
|Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
|Extraordinarily dangerous avalanche conditions. Avoid all avalanche terrain.
|Likelihood of Avalanches
|Natural and human-triggered avalanches unlikely.
|Natural avalanches unlikely; human-triggered avalanches possible.
|Natural avalanches possible; human-triggered avalanches likely.
|Natural avalanches likely; human-triggered avalanches very likely.
|Natural and human-triggered avalanches certain.
|Avalanche Size and Distribution
|Small avalanches in isolated areas or extreme terrain.
|Small avalanches in specific areas; or large avalanches in isolated areas.
|Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas.
|Large avalanches in many areas; or very large avalanches in specific areas.
|Very large avalanches in many areas.
Though we lack information from the upper elevation start zones over the past week due to a very active and stormy weather pattern inhibiting travel, we can anticipate that today will be another day of storm-snow avalanche issues including the potential for winds slabs, storm slabs, and cornice fall. These are all direct-action avalanche problems that occur during or immediately after a storm and can be exacerbated by a skier or snowmachiner in steep terrain today.
Wind slabs: With sustained winds averaging in the mid-50’s mph yesterday (and gusts to 101mph on Sunburst) wind slabs are expected to be 2-5’ deep on leeward slopes, particularly above treeline; though it is worth recognizing that strong winds such as this has a tendency to load slopes far below ridge lines, creating a mid-slope avalanche problem.
Cornices: These most recent storms have provided all the right ingredients to build monumental cornices. Sustained winds, relatively warm temps and moist snow all act to grow cornices quickly. The quicker these backcountry bombs add mass, the more unstable they become. It’ll be wise to steer clear of cornices, as these are likely to trigger a sizeable slab avalanche if falling onto a slope greater than 30 degrees today.
The stronger the prevailing winds, the lower down on the slope a wind slab will form. Graphic from rockandice.com
Storm slab: With another 1”of water at Center ridge and 8-12” of snow since Sunday night you can expect storm slabs to be 1-2’ deep and very heavy (saturated) in areas such as the Tincan trees. Micro-terrain and tree wells can act as unavoidable and dangerous terrain traps if caught up in a heavy, wet storm slab. The storm snow is settling out rather quickly in the mid-elevations but keep in mind we are still on the tail end of an active loading event today.
NOTE: In areas such as Summit Lake, the snowpack is shallower and harbors more weak layers under the recent storm snow. See Wendy’s observation and write-up from a snowboarder-triggered avalanche (Saturday) that failed on a buried surface hoar layer that ran on a mellow (30 degree) slope.
Sitting under 5-7′ of settled storm snow is a layer of old faceted snow on top of the Thanksgiving Rain Crust. As we pile more and more of a load on top of this facet/crust combo, we come closer to finding the breaking point where stress overcomes strength of the weak layer. Some of the avalanche activity we’ve seen during this past week may have ‘stepped-down’ into this deeper layer resulting in very large avalanches. The deep slab problem provides one more reason to keep terrain choices conservative until we see cooler temperatures and more stable weather allowing our snowpack time to adjust. This includes limiting your exposure time spent underneath large paths such as those that effect areas such as Johnson pass and the Lynx creek drainage.
Yesterday saw this most recent storm front move through the eastern Turnagain arm region with consistent rain falling throughout the day and overnight below about 1300′. This accounted for another 1 € of water weight (10-12 € snow above 1,500′) and another day of 100+ mph gusts on Sunburst ridge (@ 3800′). Ridgetop winds averaged in the mid-50’s from the East with temperatures in the mid 20’s F on ridgetops and low to mid- 30’s at 1,000′.
We can expect continued active weather throughout most of the day today as the tail end of yesterday’s storm moves through. The rain/ snow line will again be hovering around the 1,200′ level with up to another 6 € of snow falling in the mid and upper elevations. Temps will be in the mid- 30’s at 1,000′. Predominant winds today will be out of the east in the 25-55mph range at ridgetops and tapering off throughout the day.
Overnight and tomorrow looks to be a brief break in the storm systems before we see yet another warm, wet and windy disturbance roll through the advisory area ahead of the weekend.
|Temp Avg (F)
|Snow Depth (in)
|Center Ridge (1880′)
|Summit Lake (1400′)
|Alyeska Mid (1700′)
|Temp Avg (F)
|Wind Avg (mph)
|Wind Gust (mph)
|Seattle Ridge (2400′)
|Observation: Bertha Creek
|Schauer/ Cullen Forecaster
|Observation: Magnum & Cornbiscuit
|Moderow / St. Clair
|Observation: Tincan Backdoor
|APU Snow Science I
|Observation: Silvertip Creek
|Observation: Seattle Ridge
|John Sykes Forecaster
|Observation: Kickstep NE Bowl
|Observation: TinCan Backdoor/ Center Ridge
|AAS L1 Turnagain
|Avalanche: Lynx Creek
|Observation: Turnagain, Seattle, Mt Ascension
|Silverton Mountain Guides