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ARCHIVED - Forecasts expire after 24 hours.
Thu, April 16th, 2015 - 7:00AM
Fri, April 17th, 2015 - 7:00AM
Graham Predeger
Avalanche risk The Bottom Line

MODERATE avalanche danger exists in the alpine and at treeline elevations today where storm slabs less than 48 hours old are quickly settling out.   Human triggered avalanches in the 1-2′ range, comprised of storm snow will be possible as the snowpack continues to adjust to Tuesday’s (19 € in 19hrs) storm plus any new snow added today.   Additional avalanche concerns today will come in the form of loose or wet loose avalanches initiated by warm ambient temperatures.  

A much smaller possibility exists for large avalanches to be triggered deep in the snowpack where we know that weak snow and interfaces exist.   These are unlikely to be affected by a skier but serve as a good reminder to constantly practice safe travel protocol in the mountains.

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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.

Thu, April 16th, 2015
Above 2,500'
2 - Moderate
Avalanche risk
2 - Moderate
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
  • 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

Tuesday provided a heavy dose of localized (to Turnagain pass) storm snow in the core advisory area with up to 19” accumulating at the Center Ridge SNOTEL site (1880’) in 19 hours.  The storm quickly shut off with only a trace of snow falling yesterday allowing Tuesday’s storm slab to settle to about 12”.  This load coupled with 3-5” forecasted today is enough of a concern to warrant careful snowpack and terrain evaluation before skinning up or jumping into committing terrain.

Storm slabs/ wind slabs:

These are expected to be as deep as 1-2’ in areas affected by the wind, proving large enough to bury a person.  We don’t have a lot of information in terms of how well this recent storm is bonding to, or affecting underlying weaknesses so it’ll be prudent to pay attention to any red flags including recent avalanches, shooting cracks or whumphing prior to committing to steep terrain.  If experiencing and red flags today, these are the sure signs that the snowpack below your skis is unstable and slope angles need to be dialed back.  Quick hand pits or jumping on small (no consequence) test slopes will be a good way to gather more data while making your own snowpack assessment.

Deep slab/ persistent weak layers

This is less of a concern today but is still being pondered, particularly on the South end of the advisory area where persistent weak layers may be found closer to the surface.

With the majority of the ski season behind us, now is not the time for complacency.  Continue to practice safe travel protocols.  Ski slopes one at a time and utilize lookouts, positive communication, escape routes and islands of safety. 

Avalanche Problem 2
  • Dry Loose
    Dry Loose
Dry Loose
Dry Loose avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.
More info at Avalanche.org

Natural and human triggered sluffs are expected in the new snow on all aspects and elevations. Though the Sun isn’t forecasted to make an appearance today, warm ambient temperatures and potentially rain at lower elevations may be enough to trigger loose snow sluffing and roller balls above and below treeline. 

Thu, April 16th, 2015

Yesterday’s weather can be described as Grey-bird and warm with light winds from the east.   Temperatures reached 40 degrees at 1880′ with ridgetop winds gusting into the low 20’s mph.   Temperatures dipped to the low 30’s overnight, winds stayed calm and just a trace of snow has fallen over the darkest hours of the night.

Today a low pressure system is making its way from the Gulf of Alaska toward the Susitna valley bringing us a chance for 3-5 € of snow at 1,000′ as it moves through.   Winds will be light from the SE in the 12-20mph range with temperatures in the mid 30’s today dropping to the mid to high 20’s as this low pressure clears the Kenai Peninsula.   The potential exists for lingering snow showers to sea level by later this evening.

By Friday afternoon another low pressure and associated front will be moving into the Gulf spreading rain to coastal areas and snow showers to the higher elevations.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′)  34  1 .2    81
Summit Lake (1400′)  36  0  .02 12  
Alyeska Mid (1700′) 34    1 .2    39

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′)  25  E 8    29
Seattle Ridge (2400′)  27  n/a 11   22  
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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.