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Fri, January 4th, 2013 - 7:00AM
Sat, January 5th, 2013 - 7:00AM
John Fitzgerald
Avalanche risk The Bottom Line

The avalanche hazard remains at HIGH today above treeline, where over a foot of new snow and winds have added stress to the snowpack.   Above treeline today human triggered avalanches are very likely.   Below treeline the hazard is CONSIDERABLE, where human triggered avalanches are likely.

Fri, January 4th, 2013
Above 2,500'
4 - High
Avalanche risk
3 - Considerable
Avalanche risk
Below Treeline
Below 1,000'
3 - Considerable
Avalanche risk
0 - No Rating
1 - Low
2 - Moderate
3 - Considerable
4 - High
5 - Extreme
Avalanche risk Avalanche risk Avalanche risk Avalanche risk Avalanche risk
Travel Advice 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.
Avalanche Problem 1
  • Deep Persistent Slabs
    Deep Persistent Slabs
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.
More info at Avalanche.org

The skier triggered avalanche that occurred on Jan 2 is a good reminder that many slopes are capable of producing large, deep and destructive avalanches.  This avalanche showed us a snowpack that is remarkably dangerous, as smaller avalanches occured on adjacent slopes as a direct result of this slide.  This event should be a wake up call to us all.  While the outcome was good (no one was injured, buried or killed), it easily could have turned out much differently.  Check our observations page for a variety of reports about this avalanche.  The potential to trigger deep slabs will remain today, as over a foot of new snow combined with wind has added stress to the snowpack.  While the precip has backed off in intensity since yesterday afternoon, the snowpack needs time to adjust to its newest load.  While time will help to diminish the likelihood of triggering these deep slabs, it will not erase it.  The consequences of triggering a deep slab avalanche are severe.  Conservative terrain choices combined with safe travel practices will be essential in avoiding this problem today.

Avalanche Problem 2
  • Storm Slabs
    Storm Slabs
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
More info at Avalanche.org

While 15″ of snow is a significant load on an already stressed snowpack, 1.5″ of water weight is even more significant.  If we were to get the same amount of snow with, say, a quarter inch of water, the stress placed on the underlying layers would be much less significant.  Any time I see an inch of water or more of accumulation in a 24 hour period I pay attention.  Expect to find areas with greater accumulation, particularly above treeline and in wind loaded starting zones today.  While the sensitivity of these slabs will be on the decline, do not rule out the possibility of layers within this new snow to release and produce avalanches.  The greater problem arises when this new snow slides and brings out weaknesses deeper down into the base of the snowpack.

Fri, January 4th, 2013

The past 10 days has added a lot of weight and stress to our snowpack, as evidenced here by our friends at Alyeska resort.   While there have been brief moments of reprieve, the faucet turned back on yesterday with Turnagain Pass picking up 15″ of new snow with 1.5″ of water.   At the Sunburst station, winds have averaged 32 mph out of the E with gusts to 80.   Temps at 3800′ have been in the 20s F, with freezing levels hovering around 500′.
Today expect lingering snow showers with up to 4″ of new snow possible.   Winds will be out of the E and SE at 20-30 mph and temps at 1000′ will be around 30 F.
The extended outlook calls for a continuation of unsettled weather, with the next significant chance for snow on Saturday afternoon.


Kevin will issue the next advisory on Saturday, January 5th.

Recent Observations for Turnagain Pass
Date Region Location
11/27/23 Turnagain Avalanche: Tincan Ridge
11/26/23 Turnagain Observation: Road report: Slide with dirt on Repeat offender
11/26/23 Turnagain Observation: Pete’s North
11/25/23 Turnagain Observation: Tincan trees
11/21/23 Observation: Spokane Creek
11/20/23 Turnagain Observation: Sunburst
11/19/23 Turnagain Observation: Magnum – PMS Bowl
11/19/23 Other Regions Observation: Sunnyside/Penguin
11/19/23 Turnagain Observation: Eddies
11/19/23 Turnagain Observation: Cornbiscuit
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This is a general backcountry avalanche advisory issued for Turnagain Arm with Turnagain Pass as the core advisory area. This advisory does not apply to highways, railroads or operating ski areas.