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ARCHIVED - Forecasts expire after 24 hours.
Issued
Fri, January 2nd, 2015 - 7:00AM
Expires
Sat, January 3rd, 2015 - 7:00AM
Forecaster
Heather Thamm
Avalanche risk The Bottom Line

Today the avalanche danger is  MODERATE in the Alpine. Triggering a slab avalanche is possible in very steep terrain. Evaluate the snowpack carefully and consider the consequences before you choose to ski a steep slope.  

The Avalanche danger is LOW at treeline. Human triggered avalanches are unlikely, however it is possible an avalanche could be triggered from above and run into this elevation band. Use caution when crossing under sustained steep slopes and be aware of people above you.

There is No Rating below treeline due to not enough snow at this elevation.  

Special Announcements

The CNFAIC Avalanche Rescue Workshop schedule for January 4th has been postponed due to lack of snow at the parkinglot level in Turnagain Pass. The workshop has been rescheduled  for January 18th. Check our calendar for up to date info.  

Fri, January 2nd, 2015
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
1 - Low
Avalanche risk
Below Treeline
Below 1,000'
0 - No Rating
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
  • 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

It has been several days since a 3-day storm with high winds averaging 40mph subsided leaving behind stiff pockets of wind-loaded snow. There have been no recent reports of natural or human triggered avalanches, however the potential for triggering a wind slab in steep terrain still exists.

Wind slabs tend to be found in isolated pockets that can break above you. Avoid smooth pillow-like features on steep convexities, especially if high consequence terrain (rocks, trees, cliffs) is below you. Pay attention for shooting cracks or hollow sounding snow – these are obvious clues that a wind slab is unstable.

Evaluate the snow as you travel by probing with your ski pole to measure the stiffness and depth of the slab. Practice safe travel rituals like traveling one at a time in steep terrain and look for islands of safety to spot each other.  There are plenty of scoured ridges left behind from the 3-day wind event. Use these routes for safe travel into the alpine.

Avalanche Problem 2
  • 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

We have been actively tracking a buried surface hoar layer over the last two weeks. This layer is widespread throughout Turnagain Pass and has a 2-3’ slab sitting on top. The recent wind event has made the slab denser and more suportable. This is good news, as it will take more force to trigger this kind of avalanche. The bad news is the consequences are still high, and if you find the right spot it could propagate a large avalanche.

Avoid trigger points like shallow areas around rocks and convexities in steep terrain.  A cornice fall or wind slab avalanche could be enough weight to trigger a persistent slab. Give cornices a wide berth and pay attention to wind slabs in steep terrain as described in the primary concern.

An avalanche of this size could run into treeline. Keep in mind the runout zones and be aware of people traveling in steep terrain above you.

Buried surface hoar is still present and reactive in our test pits

Weather
Fri, January 2nd, 2015

Yesterday there was no new precipitation, skies were overcast and winds were moderate (10-25mph) from the Northwest. Overnight temperatures have started to drop into the low 20’s F.  

Northwest winds (10-25 mph) will decrease slightly this afternoon as temperatures cool into the teens tonight.  Light snow flurries are possible today.

A high pressure system in the artic is building and is the culprit behind the cooling trend. Northwest winds are expected to decrease and light snow flurries may accompany mostly clear skies and cool temperature (10 to 25 F) into the weekend.

PRECIPITATION 24-hour data (6am – 6am)

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 28   0   0   34  
Summit Lake (1400′) 29   0   0    6
Alyeska Mid (1700′) 28 0   0   26  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 20   NW   9   26  
Seattle Ridge (2400′) 22   W   14   44  
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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.
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