|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.
Yesterday a party on Pastoral found the trigger point for a large (D3: could bury and destroy a car, damage a truck, destroy a wood frame house, or break a few trees) deep slab avalanche. The crown depth was estimated to be around 10 ft. deep. This avalanche was triggered from below as the two were crossing the slope. They reported, “It sounded like a distant explosion when it went, then we heard and felt the snowpack below us drop several inches.” When this was triggered it also sympathetically released a slope approximately half a mile away. Last Friday the forecast said, “This deep persistent slab problem and will be guilty until proven innocent. The 1st person on the slope or the 10th might trigger this type of avalanche. It is a total roll of the dice or Russian roulette set-up. Finding the shallow spot could have devastating results. This type of avalanche would be unsurvivable. There may be no obvious clues to indicate instability and digging to find the weak layer could be challenging.” The verdict is out. This snowpack set-up is guilty and could be a scary issue for quite a while. The combination of faceted snow on or under a crust near the ground with a stiff slab above makes for an instability that is contiguous over terrain. A collapse of the weak layer in one spot can propagate/communicate a failure across the area. Translation: I step here. It avalanches over there. The way to manage this is to avoid avalanche terrain specifically in the Alpine. Shallow areas are more likely to be trigger points to cause the failure. This avalanche emphasizes paying attention to what is above you, what the terrain you are on is connected to and where other groups are. Thanks to the party involved for sharing details and all the other observations submitted.
Photo: Mike Ausman
Crown photo: Mike Ausman
Photo of debris: Stephen Ellison
Yesterday observers reported stiff wind affected snow in the Alpine. There is still snow to move around and winds are forecasted to be easterly, gusting into the 40s today. Wind slabs will be possible on steep, leeward, loaded slopes. Look for drifting, cracking and pay attention to stiff snow under foot. Even a small wind slab can be very dangerous in high consequence terrain. In addition, give cornices a wide berth. They have been growing with each new snow and loading event.
Wind loading and cornice along -1/Warm-up Bowl.
Yesterday was partly cloudy. Winds were westerly 10-20 gusting into the 30s. Temperatures were in the 20Fs. Overnight skies cleared and temperatures cooled into the low 20Fs and teens as an inversion set-up.
Today will be clear and sunny with some valley fog. Temperatures will be in the teens and low 20s. Winds will be easterly 15-25 gusting into the 40s. They are forecasted to increase tonight into Friday.
Friday will be partly cloudy with a chance of snow. Easterly winds will blow 30-40 mph with gusts into the 50s. Temperatures will be in the mid 20Fs to low 30s. Saturday looks to be partly sunny as the storm track for the weekend has shifted and there is less precipitation forecasted for the advisory area but we may get a few inches for the holiday.
* Sunburst weather station is down due to loss of battery power.
PRECIPITATION 24-hour data (6am – 6am)
|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: Kickstep NE Bowl
|Observation: TinCan Backdoor/ Center Ridge
|AAS L1 Turnagain
|Avalanche: Lynx Creek
|Observation: Turnagain, Seattle, Mt Ascension
|Silverton Mountain Guides
|Observation: Tincan Trees
|Dalpes/Thamm/ Schauer Forecaster
|Observation: Seward Highway across from Johnson Pass TH
|Avalanche: Base of Seattle Ridge
|Troy Tempel, Thomas Lees, .Josh Bollaert, Damian Naquin
|Observation: Lynx creek