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ARCHIVED - Forecasts expire after 24 hours.
Issued
Wed, April 15th, 2015 - 7:00AM
Expires
Thu, April 16th, 2015 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

UPDATE for Wednesday April 15th, 7am:

Turnagain Pass has seen 19″ of new, low density, snow in the past 19 hours!!  This is great news for those still interested in winter but caution is warranted if you are headed out in the backcountry.  The  avalanche danger has risen to  CONSIDERABLE  for wind/storm slab and loose snow avalanches associated with rapid loading of new snow. Sluffs will be large and high volume and slabs could be as thick as 2′ or more on windloaded slopes; the good news is the ridgetop winds have been moderate from the East (20-30mph) with gusts in the 40’s.  The 24-48 hour rule applies today – this means let the new snow settle out and bond for a day or two before getting on the steep slopes.  

The Pass is expecting another 2-4″ today intermixed with some clearing skies. Ridgetop winds will be 10-15mph from the East.

See yesterday’s Avalanche Advisory  HERE  which speaks to the storm snow instabilities that will be seen today, Wednesday.

Snow to the road. Photo is from 7:45am Wednesday, AKDOT&PF Snow Stake at 1,000′ on Turnagain Pass

Special Announcements

We are currently issuing advisories 5 days a week until our final advisory on Thursday, April 30th.   Advisories will be posted at 7 am each day except Mondays and Wednesdays.

Wed, April 15th, 2015
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
3 - Considerable
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

After waiting for months, it seems winter is finally trying to show up. We have another storm system moving in today which is expected to add 2-6″ of new snow and another 2-6″ tonight – snow should make it to sea level. Avalanche conditions will bemostly related to how much new snow accumulates, however there are some concerning layers deeper in the pack to keep in mind (more on that below).

WIND SLAB and STORM SLAB:

Wind slabs forming on leeward slopes will be fairly shallow (4-8″ thick) today. Even in areas seeing little new snow, these should build due to 6-8″ of existing loose snow available for transport. With continued snowfall overnight, wind slabs could be in the 10-14″ thick range tomorrow – which will be more of a concern. Areas out of the wind, where up to a foot of new snow may fall by tomorrow, could see slabs as well. If you are headed out, monitoring the new snow with quick hand pits and/or using your pole to check for stiffer/denser snow over softer/weaker snow will be good ways to assess slab development.

LOOSE SNOW AVALANCHES (SLUFFS):

Natural and human triggered sluffs are expected in the new snow on all aspects and elevations. When the sun comes out, possibly tomorrow, watch for wet/damp sluffs on Southerly aspects.

CORNICES:

Cornices will continue to grow and fall naturally with this warm(ish) storm.

 

Avalanche Problem 2
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

The mountains are currently in a transition period from winter to summer which means a highly variable snowpack that changes dramatically with aspect and elevation. In short, Northerly slopes have weak faceted snow sitting anywhere from 2-8′ below the surface; this spread is so dramatic due to the snowfall amounts during last week’s storm. The South side of Turnagain Pass has a thinner snowpack and therefore these weak layers are more concerning. On Southerly slopes, a stout crust exists below the storm snow from last week (2-4′ below the surface). Initial bonding was poor and though stronger now, still a concern.

What this all boils down to is: triggering an avalanche that fails deeper in the pack, although not likely, is not out of the question. Remember your safe travel protocol: expose one person at a time, have escape routes planned, watch your partners and know how to effect a rescue if a slide is triggered.

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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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