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Mon, December 23rd, 2013 - 7:00AM
Tue, December 24th, 2013 - 7:00AM
John Fitzgerald
Avalanche risk The Bottom Line

The avalanche hazard is MODERATE today above and below treeline.   It will be possible for large triggers such as snowmachines or groups of people to trigger slabs up to 2 feet in depth on steep terrain today.   Isolated pockets of newly formed wind slabs will also be an issue to contend with in higher elevation terrain with an Easterly component.

Mon, December 23rd, 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
  • Persistent Slabs
    Persistent Slabs
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
More info at Avalanche.org

Over the past several weeks snowfall has come in small doses.  This has helped to slowly build a slab on top of a generally weak foundation.  Due to the gradual nature of these loading events, avalanche activity has been spotty in nature.  Yesterday we received reports of two human triggered avalanches in mid elevation terrain (one report HERE).  We have been experiencing collapsing for several days in a row at all elevations but not widespread avalanche activity.  What this boils down to is that we are in the “gray zone” of MODERATE avalanche hazard.  The snowpack structure is poor in most areas-there is a slab (up to 24”) sitting on weak snow near the ground.  But there has not been quite enough of a load to create instability that is obvious and easy to predict.

Because of this, it is worth continuing to treat slopes above 35 degrees with suspicion.  Cooler temperatures today will likely make the snow less reactive but the potential still exists for skiers or snowmachiners to trigger slabs up to 2 feet in depth.  Exposing only one person at a time to steep terrain, spacing out across slopes and communicating your plan within your group will help to minimize your exposure to avalanche hazard.     

Avalanche Problem 2
  • 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

Winds overnight kicked up into the 30-40mph range (with gusts to 61mph) out of the Northwest on Seattle Ridge.  The winds at Sunburst have been significantly less (5mph average).  Because of this, these slabs will be scattered about in pockets on primarily East facing terrain. Fresh new wind slabs will exist in pockets and will be most sensitive on steep slopes above treeline.  Avoid snow in starting zones or above cross loaded gullies that have a smooth, rounded look to it. With this new load the potential also exists for smaller wind slabs to pull out deeper weak layers in the snowpack.

Mon, December 23rd, 2013

In the past 24 hours the mountains around Eastern Turnagain Arm have picked up a trace of new snow.   Temperatures have been on the decline with daytime averages yesterday in the mid twenties F and current ridge top temps in the single digits to teens F.   Winds at the Seattle Ridge Station over the past 12 hours have averaged 30mph out of the NW.

A small ridge of high pressure will build over the area today, bringing clear skies and cooler temps.   Winds will blow out of the NW at 20-30mph and temperatures will climb back up into the teens to low twenties F.

The ridge over us today will be forced out by a complex low pressure system which will move into Southcentral Alaska tomorrow evening.   We can expect snowfall to be light and temperatures to rise between Tues and Thursday of this week.

Recent Observations for Turnagain Pass
Date Region Location
05/13/24 Turnagain Observation: Eddie’s, Sunburst, Seattle, Cornbiscuit, Pete’s South
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05/07/24 Turnagain Observation: Turnagain Pass Wet Slabs
04/29/24 Turnagain Avalanche: Turnagain aerial obs
04/27/24 Turnagain Observation: Johnson Pass
04/23/24 Turnagain Observation: Turnagain Sunny Side
04/21/24 Turnagain Observation: Bertha Creek
04/20/24 Turnagain Avalanche: Spokane Creek
04/16/24 Turnagain Observation: Cornbiscuit
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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.