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ARCHIVED - Forecasts expire after 24 hours.
Mon, January 21st, 2013 - 7:00AM
Tue, January 22nd, 2013 - 7:00AM
John Fitzgerald
Avalanche risk The Bottom Line

Today the avalanche hazard is MODERATE above treeline.   A moderate amount of new snow and wind has created slabs that will be sensitive to human triggers.   The possibility still remains for large and destructive avalanches to be triggered in the higher elevations today.   The hazard below treeline is LOW this morning and will rise to MODERATE, as rising temperatures will slightly increase the chances for humans to trigger avalanches today.

Mon, January 21st, 2013
Above 2,500'
2 - Moderate
Avalanche risk
2 - Moderate
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
  • 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

Recent snow in the higher elevations have fallen on slick and hard surfaces.  While the snowfall amounts have been modest, the winds overnight have been transporting this snow onto leeward aspects, mainly West to North facing slopes.  With temperatures forecasted to increase throughout the day, expect these slabs to become more sensitive to human triggers.  Expect to see shallow pockets of windslab at mid elevations (up to 1800′) in open areas to be the most sensitive today, as these slabs have fallen on a firm crust and will heat up more readily than slabs in the higher elevations today.  On the flip side, these slabs are not as large (<6″) as slabs in the upper elevations (>12″).  Avoiding steep upper elevation starting zones which have a pillowy or wind affected look will also be important, as these slabs, once released, have the potential to carry people downslope and into terrain traps 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

It is important to not forget the poor structure of the base of our snowpack.  Snowpit tests over the past week continue to show weak faceted snow persisting near the ground.  The large dense slabs that formed over the holidays are now able to support a lot of weight.  The chances of initiating one of these slabs is getting more difficult by the day.  If you were to trigger one of these deep slabs, the outcome would be bad, as the volume of snow could be very large.  We are clearly in a dormant period for this avalanche problem, as it has been a week now since any new deep slab activity has been reported.  Unfortunately, the weak snow is being well preserved in many areas and will continue to lurk well below the surface for the forseeable future.  Staying away from areas showing exposed rocks, ground or vegetation will be important in avoiding this problem today, as these are the most likely areas to trigger a deep slab avalanche.

Mon, January 21st, 2013

In the past 24 hours Turnagain Pass has received ~6″ of new snow with .3-.5″ water equivalent. Winds have been moderate out of the E and SE averaging 20 mph with gusts to 36 mph.   Temps, which have been on a steady rise overnight have averaged near 32 F at 1800′, and in the mid 20s F at 3800′.
Expect clouds to be on the increase through the day, winds out of the East 20-35 mph and a chance of precipitation with up to 3″ of new snow possible in the mountains.   Temperatures will climb into the mid 30s F at 1000′.
The extended outlook calls for a greater chance of snow tonight, with precip continuing into the middle of this week.


Wendy will issue the next advisory, tomorrow morning January 22nd.

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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.