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Sun, February 22nd, 2015 - 7:00AM
Mon, February 23rd, 2015 - 7:00AM
Graham Predeger
Avalanche risk The Bottom Line

The avalanche danger is CONSIDERABLE today above 2,000′ where wet snow has increased the stress on an untrustworthy persistent weak layer.   Add a person into the mix and human-triggered avalanches are likely on slopes greater than 35 degrees.   Moderate Easterly winds are also increasing the likelihood of wind slabs 12-24 € deep in the upper elevations.

The danger is MODERATE below 2,000′ as it is important to recognize that an avalanche initiated in the Alpine can entrain enough snow in isolated areas (funneled terrain) to run debris well below our current snow line.   This is an €œoverhead hazard € and important to keep in mind in places such as Portage Valley or the Byron Glacier trail.

Special Announcements

Iron those Carhartts, break out the sequins, and dust off the bolo €¦its Snowball time! Please join the Friends of the Chugach National Forest Avalanche Information Center and Alaska Avalanche School at Taproot for an €œAlaskan Formal € night at 7pm on February 27th.  You won’t want to miss this event!

Sun, February 22nd, 2015
Above 2,500'
3 - Considerable
Avalanche risk
3 - Considerable
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
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

A perfect recipe for dangerous avalanche conditions exist in the 2,000 – 3,000’ elevation band where a uniform weak layer of faceted snow lies in wait 6” to 3+’ below the surface.  Level 2 avalanche course students were experiencing large collapses (whumphing up to 100’ radius) on this faceted layer yesterday, proving there is a significant amount of energy within the weak layer.  This translates to good potential for an avalanche to propagate across a slope if initiated. 

Yesterday’s storm has increased the load overlying this weak layer with wet snow falling above 2,000’ (and rain below).  Human triggered avalanches are likely on slopes steeper than 35 degrees.  This most recent load may just be enough to initiate a natural avalanche cycle as well, though visibility yesterday was hampered to the point where no natural avalanches were observed.

If you travel in the backcountry today, it’ll be imperative to stick to mellow terrain and avoid steeper connected slopes or runout zones.  If you are in a runout zone or on a mellow slope connected to a slope greater than 35 degrees, you’re in avalanche terrain.  Remember, you cannot necessarily manage the weather or the snowpack right now but you can always manage your terrain choices to ensure a safe day in the backcountry.

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

Moderate Easterly winds combined with new snow in the upper elevation start zones have been, and will continue to actively build fresh wind slabs 12 – 24” today on leeward slopes.  These could be a problem in and of themselves but also have the potential to step down into deeper weak layers, possibly creating large avalanches.  

Additional Concern
  • Normal Caution
    Normal Caution
Normal Caution
Normal Caution means triggering an avalanche is unlikely but not impossible.
More info at Avalanche.org

Below 2,000’ what snow that is on the ground has been well adjusted to the recent rain and warm temperatures.  The greatest hazards at these lower elevations come in the form of avalanches initiating in the mid to upper elevations and debris travelling in funneled terrain well below our rain/ snow line. 

Moreover as bizarre as it is to say in late-February, early season conditions do exist.  Thin snowpack, icy approaches and water crossings are all real hazards right now in the lower elevations.

Sun, February 22nd, 2015

Yesterday was marked by another warm, wet North Pacific low pressure system that brought steady rain to southcentral Alaska below about 2,000′.  Ridgetop temperatures were in the high 20’s with sustained winds in the 20-35mph range from the NE.  Girdwood appears to be the precip winner with 1.16″ of water in the past 24 hours as temperatures remained in the high 30’s at sea level throughout the day.  

More warm air is on tap across our region though rainfall looks to be more intermittent today than yesterday.  Expect temperatures to be in the upper 30’s at 1,000′ with up to a quarter inch of water forecasted.  The rain/ snow line again will be somewhere in the 2000 – 2200′ range today with ridgetop winds out of the east in the 15 – 30mph range.

On Monday the weather models hint at (relatively) colder air moving in from the west coupled with continued moist flow though precip amounts are quite nominal at this point.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 35   0  .3    42  
Summit Lake (1400′) 35  0   .3 7  
Alyeska Mid (1700′) 35    1/ rain  1.16  25

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′)  27  n/a n/a   n/a  
Seattle Ridge (2400′) 29  n/a 23   58  
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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.