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ARCHIVED - Forecasts expire after 24 hours.
Issued
Tue, December 24th, 2013 - 7:00AM
Expires
Wed, December 25th, 2013 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

We continue to have an overall  MODERATE  avalanche danger for triggering a slab avalanche 1-2′ deep. Areas most likely to find and trigger an avalanche are steep wind loaded slopes on East and South aspects near and above treeline. We had a short lived natural wind slab avalanche cycle yesterday morning associated with strong Northwest winds. More on that below.

Tue, December 24th, 2013
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
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. 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
  • 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

Though the main event for yesterday was the wind, our main concern still lies with the potential for triggering an avalanche that fails in the weak snow at the base of the pack. After the past day of cold temperatures, the likelihood for triggering one of these larger slides is decreasing but the problem is not gone – our poor snowpack structure remains and so should our wariness. Keeping with safe travel practices, such as exposing only one person at a time, is wise if venturing onto steep slopes. Yet, if you wish to avoid any avalanche problems all together, stick to gentler terrain 35 degrees or less.

Below is a picture of a couple wind slab avalanches on Seattle Ridge just above the motorized lot that occurred yesterday. It is hard to see but these wind slabs look to have stepped down, or scoured down, into the weak November snow. This highlights our main concern.

Two natural wind slabs on the Southeast face of Seattle Ridge (3,000′). 

We had a peak in reactivity for these persistent slabs on Sunday where two human triggered avalanches occurred. At least one of these (on Eddies) was a remote trigger. The other one (on Magnum) is unclear. See the investigation from the Magnum avalanche HERE.

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

For anyone that was in the Girdwood/Turnagain/Summit zone yesterday morning, it was hard not to notice the high winds ravaging the mountains. Plumes were widespread and so was a short lived wind slab cycle. Below are a few photos from this event. The winds spiked for 3 hours, along with the avalanche activity, then quickly died down for the afternoon.

Today, watch for lingering wind slabs left over from this wind event – most likely on East and South aspects. These should be stiff and stubborn to trigger but still possible – avoid steep slopes with wind drifted and hollow feeling snow. More importantly, the chance of triggering a wind slab that breaks in the deeper weak layers mentioned above is possible – making for a larger slide, similar to the Seattle Ridge avalanche yesterday.

Plumes along peaks and ridges                                               Natural wind slab on East facing Fresno Peak
 

More details on these avalanches can be found HERE.

Weather
Tue, December 24th, 2013

Yesterday clear skies and cold temperatures were accompanied by strong Northwest winds. The winds averaged 53mph for 3 hours in the late morning and have since died down and switched to the East early this morning. Temperatures have been in the 0-10F range during the past 24 hours and are just starting to climb out of the single digits.

Today we should see these temperatures reach the mid-teens at most locations, except for valley bottoms, and wind increase to the 10-20mph from the East. A few clouds look to stream in as well as a series of low pressure systems skirts us to our South. We are too far north to get much for snow but we might squeak out a trace to an inch by Christmas morning.

For Christmas this year it looks like we will get a nagging area of high pressure that will bring clear skies and somewhat cold temperatures (teens) through Sunday. Our next shot of precip is not in the foreseeable future.

Observations
Recent Observations for Turnagain Pass
Date Region Location
11/16/23 Turnagain Observation: Tincan Common
11/14/23 Turnagain Observation: Sunburst/Magnum
11/14/23 Turnagain Observation: Seattle Ridge
11/13/23 Turnagain Avalanche: Tincan Trees
11/12/23 Turnagain Observation: Sunburst
11/12/23 Turnagain Avalanche: Goldpan – avalanche
11/11/23 Turnagain Observation: Tincan Common
11/11/23 Turnagain Observation: Taylor Pass – Sunburst
11/10/23 Turnagain Observation: Tincan
11/10/23 Turnagain Observation: Tincan Trees
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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.