Avalanche Advisory Archive 2016 – 2018

Date Issued:2017-01-07 08:15:55
Danger:2
Primary Trend:3
Primary Probability:3
Primary Likelihood:3
Primary Size:2
Primary Description:

These Taku wind events directly load our urban enviroment in places.

Be aware that danger is increased in windloaded areas.

Be aware that with winds this high snow can deposit in unusual places. If you find new snow deposits from windloading be aware these are areas of increased concern.

Secondary Trend:2
Secondary Probability:5
Secondary Likelihood:2
Secondary Size:3
Secondary Description:

As we see increased windloading one of the concerns is we place enough mass on these deep hard slabs to actually get the slab to a state of instability. This could be 3-6' deep in places.

The odds of triggering this layer are not good and yet should it be triggered these will be VERY LARGE avalanches... Reduce your esposure to large avalanche paths and avoid spending time in them.

Once again although not likely to be triggered these slides on the deeper weak layer in place are possible. Especially in our urban enviroment along the channel.

Discussion:

The National Weather Service Forecasts-

Today- Locally very windy. Mostly sunny. Highs 18 to 24. Near downtown juneau and douglas...northeast wind 20 to 30 mph with gusts to around 80 mph. Elsewhere...northeast wind 10 to 20 mph.

Tonight- Locally very windy. Clear...colder. Lows 5 to 18...warmer near downtown juneau and douglas. Northeast wind 10 to 15 mph...except northeast 20 to 30 mph with gusts to around 65 mph near downtown juneau and Douglas.

Sunday- Locally very wind. Sunny. Highs 19 to 25. Northeast wind 15 to 25 mph. Near downtown juneau and Douglas... northeast wind 25 to 35 mph with gusts to around 65 mph. Wind chill to 20 below in the morning.

We have seen a fair drop in temperatures over the last 2 days. Yesterday morning Eaglecrest was reporting 16f degrees. This morning they are in single digits at 9f degrees. Mt Roberts is hovering closer to 11f degrees. The forecast calls for another 4-5degrees of cooling over the next 24 hours.

Winds have been blistering around the region with the icefield and sheep mountain seeing 100+ mph winds. This can create serious loading in places.

Oddly enough some of the areas with the most wind may have the least danger... as with 100mph winds nothing is deposited everything is stripped away. Areas with mild to moderate winds may be seeing more loading and danger because these milder winds allow all the snow being transported to come to rest.

With high winds hard slabs can be created and are much harder to trigger and yet also much more dangerous should you trigger and be involved.

With high winds and loading avalanche danger remains MODERATE to Considerable today. Natural avalanches and human triggered avalanches are both possible.

We aware out there and use extra caution in the areas you choose to recreate. Routefinding is key.

Tip:

Hard Slab Avalanche

A slab avalanche of hard, dense snow.

Hard Slab Avalanche:
Hard slabs are stiff, cohesive slabs, usually deposited by strong wind drifting or the slabs may be old, hardened layers of snow. Think of them like a pane of glass on top of potato chips. The good news is that hard slabs are more difficult to trigger than soft slabs, but the bad news is that they tend to propagate farther and make a much larger and more deadly avalanche. Also, the stiffer the slab, the farther above you the fracture line will usually form, and the harder it will be to escape. The reason for this is that stiff slabs tend to spread a person's weight over a larger area. Even with very poor weak-layer bonding directly beneath the person, a stiff slab can bridge outward to places where the slab might be better bonded to the bed surface, like a drunkard stumbling along supported on the shoulders of two sober friends.

Hard slabs are especially tricky because the stiffness and/or thickness of slabs can vary a lot from place to place, so just because you may not be able to trigger a slab in a thick spot, as soon as you get to the edge of the slab--for instance where it may thin near a ridgeline--you may be able to trigger the whole slope.

Forecaster:Tom Mattice