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ARCHIVED - Forecasts expire after 24 hours.
Mon, February 4th, 2013 - 7:00AM
Tue, February 5th, 2013 - 7:00AM
John Fitzgerald
Avalanche risk The Bottom Line

The avalanche hazard is MODERATE above treeline today, where recent snow and winds have formed slabs that will be sensitive to human triggers in the higher elevations today.   The hazard below treeline is LOW today, where the snowpack has been able to absorb light rain and wet snow to the point where it will be difficult for humans to trigger avalanches today.

Mon, February 4th, 2013
Above 2,500'
2 - Moderate
Avalanche risk
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. Dangerous avalanche conditions. 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

Light to moderate snowfall over the last three days has formed new slabs that will be easy to trigger in steep wind loaded terrain today.  In areas that have not received wind and on slopes under 35 degrees the new snow has been bonding well to older snow surfaces.  All reported avalanche activity in the past several days has occurred around the 2,800′ elevation.  This is due in large part to snow falling on a firm surface that has encouraged propagation across slopes.  While these avalanches have released snow in relatively large areas, the volume has been low enough that people have been able to avoid injury and burial.  While we have limited information from the upper elevations lately, snowfall amounts and winds have been high enough above 3,000′ to create dense slabs up to 18 inches in depth.  Throw into the mix new snow and winds today and slabs will increase in size and depth.  Sticking to slopes under 35 degrees and avoiding wind loaded starting zones will allow for enjoyable riding and skiing conditions today.

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

The deep slab problem is elevation dependent.  The snowpack between 1,000 and ~2,000 feet has been through four periods of warm temps, light rain and wet snow in the last month.  This has helped to change the structure of the snow at the ground to the point where it is generally not a concern.  However, above ~2,000 feet the snowpack is still in transition; snow pits have shown us that the weak snow at the ground is changing for the better.  However, as you gain elevation the weak snow at the ground is more intact and more of a problem to pay attention to.  Avoiding thin spots, steep rollovers, and terrain that doesn’t offer exit options is the best way to stay away from this problem.

It has been three weeks since a deep slab avalanche has been reported in the area.  It is now very difficult to affect weak layers at the ground.  The consequences still remain high, as a deep slab avalanche once triggered could entrain high volumes of snow and do a lot of damage.

Mon, February 4th, 2013

Turnagain Pass has picked up 1-2″ of new snow in the past 24 hours.   Winds yesterday were light but have picked up this morning and are now blowing 20mph out of the East with gusts to 36.   Temps have been mild with freezing levels hovering around the 1,000′ elevation.

Snowfall should continue today, with possible accumulations in the 2-4″ range.   Ridgetop winds will blow out of the S and SE between 15-20 mph with gusts up to 30mph.   Temps at 1,000′ will be just below freezing.

A generally unsettled pattern will continue this week as a series of disturbances move through the area.   Snowfall amounts will continue to be light and temps should remain mild and similar to what we have seen over the last several days.


Wendy will issue the next advisory tomorrow morning, February 5th.

Recent Observations for Turnagain Pass
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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.