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ARCHIVED - Forecasts expire after 24 hours.
Issued
Mon, January 6th, 2014 - 7:00AM
Expires
Tue, January 7th, 2014 - 7:00AM
Forecaster
John Fitzgerald
Avalanche risk The Bottom Line

The avalanche hazard is CONSIDERABLE above and below treeline today.   It will be possible for snowmachiners, riders and skiers to trigger dangerous slabs up to 3 feet in depth on slopes at and above treeline.   Below treeline, warm temperatures will make it easier to trigger slabs up to 2 feet in depth on steep slopes, gullies and rollovers.

Special Announcements

CNFAIC forecaster Wendy Wagner will be giving a free talk on Avalanche Awareness at REI in Anchorage Tuesday night at 6pm.   The course is currently full, but check with REI Anchorage to get on the waitlist.

Mon, January 6th, 2014
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
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
  • Persistent Slabs
    Persistent Slabs
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
More info at Avalanche.org

The snowpack received a serious shock over the weekend.  Over a foot of new snow fell in a short period of time on Saturday night Jan. 4th.  This resulted in widespread natural avalanching throughout the forecast area.  High winds have eroded the snow near many of the areas that have avalanched, making it hard to see this evidence.  Yesterday we were able to see this evidence but it was not blatantly obvious.

What we do know is that the snowpack still has a weak foundation.  Time will allow the snowpack to adjust to this newest load to some degree.  However, it has been only one day since we have had significant natural avalanche activity.  The snowpack simply needs more time to adjust.  The consequences of triggering an avalanche right now are potentially severe.  

Dense slabs ranging between 1-3 feet deep are laying in wait for the right trigger.  This may come in the form of a large group, or it may just take one person to hit a thin spot in the slab.  Now is an important time to recognize and avoid likely trigger points.  Areas of shallow snow, convexities and steep slopes should be avoided today.

Below is an image of one of many large natural avalanches that occured over the weekend.

Todd's

Avalanche Problem 2
  • Wind Slabs
    Wind Slabs
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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

New snow, warm temperatures and moderate wind (out of the East) will make it possible for humans to trigger shallow new wind slabs in steep terrain.  These slabs on their own will not be large.  However, triggering one of these newly formed slabs will have the potential to trigger deeper weak layers in the snowpack.  It will be important to avoid steep slopes especially in areas receiving 6 or more inches of new snow and wind today.

Weather
Mon, January 6th, 2014

In the past 24 hours a trace of new snow has fallen on Turnagain Pass.   Girdwood valley has picked up another 3-5 € of snow.   Temperatures climbed overnight with ridge top stations in the high 20s F with the Turnagain Pass SNOTEL (1,880′) showing an overnight high of 36 F.   Winds at the Sunburst station have been light to moderate out of the East averaging 18 mph.

Today expect cloudy skies and snow showers mainly in the first half of the day.   Snow accumulation of 4-6 € are possible.   Ridgetop winds will be out of the East at 25-30 mph.   Temperatures will remain mild, in the low to mid 30s F at 1,000′.

The weather pattern to our South and West is complex.   Computer models are doing a poor job of projecting weather beyond today.   Expect unsettled weather over the next several days with modest precip amounts and generally mild temperatures.

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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.