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ARCHIVED - Forecasts expire after 24 hours.
Issued
Thu, January 31st, 2013 - 7:00AM
Expires
Fri, February 1st, 2013 - 7:00AM
Forecaster
Graham Predeger
Avalanche risk The Bottom Line

The avalanche danger remains MODERATE today with human triggered avalanches possible.   Pay particular attention to areas at and just above tree line where these wind slabs have gained in mass over the last 24 hours and are sitting on top of a supportable crust.   Below tree line the danger is LOW where we have a few inches of moist snow resting on a strong, supportable crust.

Thu, January 31st, 2013
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
1 - Low
Avalanche risk
Below Treeline
Below 1,000'
1 - Low
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

Tender wind slabs will once again dominate the discussion today as the primary avalanche concern.  Yesterday these wind slabs were shallow and easily triggered on steep convex slopes.  With the added wind yesterday and a few more inches of snow overnight we can expect these wind slabs to have gained in depth and mass. The deeper, more dangerous pockets will be found on slopes with a westerly tilt at and above tree line where these slabs are resting on a smooth and supportable crust.  At higher elevations where the crust is not present, there is some uncertainty as to how well this most recent snow is bonding.  It will be sensible today to pay attention to any red flags including shooting cracks, whumphing or recent avalanches.  These are your bulls-eye clues that instability in the snowpack exists.

            Shooting crack in shallow wind slab at 2500′.  Jan. 30th, 2013.  Petes North

Avalanche Problem 2
  • Deep Persistent Slabs
    Deep Persistent Slabs
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.
More info at Avalanche.org

This problem has been dormant for some time now.  It’s unlikely this most recent storm will provide enough of a punch to wake up this problematic layer.  However, it is prudent to continue to be suspect of steep, shallow and rocky terrain above tree line where it is more likely a human could impact this deeper, weak snow.

Weather
Thu, January 31st, 2013

Forecasted precipitation fell a little flat for us yesterday and last night with the Turnagain pass region only picking up about 1-2 € of new snow.   Winds have dropped off substantially overnight as this latest front weakens and moves out of our area.  

This last day of January doesn’t look to be like much of a weather producer in our region.   Temperatures are expected to be in the low 30’s at 1000′, winds light from the east and less than an inch of new snow in the forecast.   Another weak front moves into the gulf tomorrow ushering in a chance for snow/ rain in south central as we head into the weekend.

January 2013 comes to an end with 9.1 € of water and 71 € of snow (preliminary numbers), most of which fell in the first half of the month.

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Fitz will issue the next advisory tomorrow morning, February 1st.

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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.