Turnagain Pass RSS

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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sat, March 4th, 2017 - 7:00AM
Expires
Sun, March 5th, 2017 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger is  MODERATE  on slopes above 2,000′ that have seen wind loading by  sustained Northwest winds. Although these wind slabs are expected to  be very stiff and stubborn to trigger, the  possibility remains that slabs could release in steep rocky terrain. In areas that have seen less wind, such as many slopes in the core forecast area of Turnagain Pass, triggering a wind slab is unlikely.  

There is a LOW avalanche danger on upper elevation slopes without recent wind loading and all slopes below 2,000′.  

*In Summit Lake, Girdwood Valley, and on the southern end of the forecast zone a generally shallower snowpack exists with a poor structure. Wind loaded slopes in these areas have the potential to step down and trigger a deeper avalanche. Please see  the Saturday Summit Summary  HERE.

Special Announcements

Strong winds over the past several days have affected the snow/avalanche conditions in many areas of Southcentral Alaska and the Kenai. See this report sent in to us from  the Lost Lake zone  on the Southern Kenai. Additionally, a natural avalanche was viewed in motion in the South Fork of Eagle River yesterday. For avalanche conditions at Hatcher Pass, see the HPAC Saturday morning advisory!

Avalanche Rescue Talk:  Stop by Ski AK in Anchorage for a discussion on backcountry rescue Tuesday evening! The focus will be on organized rescue, presented by Bill Romberg (AMRG) a rescue specialist with 150 Search and Rescue missions here in Alaska. The evening will begin with a short ‘state of the snowpack’ report by the CNFAIC. See you Tuesday night – more details  HERE!!

Sat, March 4th, 2017
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

As Southcentral Alaska sits under a cold, clear and very windy weather pattern, there are areas that have been partially spared by the brunt of the Northwest winds. The ridges along the East side of the road along Turnagain Pass are one of these areas. Folks have been able to find some soft snow and venture further into the mountains without incident. That said, there are areas that have not escaped the major winds. An example would be the Crow Pass region of the Girdwood Valley and the mountains on the Southern end of the forecast zone toward Silvertip. In the Summit Lake area (Summit Snowpack Summary here) two avalanches were seen yesterday on Summit Peak. The key, of course, is to find these sheltered areas, both for better riding conditions but clearly for decreased avalanche danger.

Wind slab avalanches:

It will be another day to watch for slopes with recent or current wind loading. Ridgetop winds should again be moderate to strong – in the 15-25mph range from the Northwest. However, there is not nearly as much snow to blow into slabs as there was at the beginning of this wind event 4-5 days ago. Most of the loose surface snow has blown away or been blown into hard slabs, crusts and sastrugi at the higher elevations. Things to keep in mind with wind slabs:

  1. Wind slabs are expected to be very hard and stiff (supportable to boots and snowmachines)
  2. They are likely to be stubborn and tough to trigger
  3. Steep rocky terrain is the most likely place to trigger a slab

  

Cornbiscuit Ridge on the East Side of Turnagain Pass – one of the ‘less windy’ areas.

Additional Concern
  • 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

It is good to keep in mind that there are areas in the periphery of Turnagain Pass that have a poor snowpack structure. These layers are buried surface hoar 1-3′ deep and facets in the mid and base of the snowpack. The ‘wind event’ has loaded and reactivated some of these older layers. The most recent avalanche activity was seen yesterday in the Summit Lake area. Besides Summit Lake, other areas of concern include the Johnson Pass zone and some areas in the Girdwood Valley. Continual winds with this relentless wind event may be loading these old weak layers to the point of failure.

Recent natural wind slabs in the Summit Lake area, this is just to the South of the forecast zone, seen and documented yesterday. (A bit complicated, but the point is two of the 4 avalanches in the photo occurred yesterday).

Weather
Sat, March 4th, 2017

Brilliant sunny skies were over the area yesterday with very cold temperatures at all elevations – in the single digits and minus single digits. Daytime warming allowed the mid and lower elevations to warm into the upper teens and have only cooled a few degrees overnight. Ridgetop winds during the past 24-hours have averaged near 10mph with gusts into the 30’s from the Northwest.  

As Southcentral Alaska sits in a holding pattern of sorts, we can expect similar sunny skies today with continued Northwest winds. Temperatures should warm again today into the upper teens below 3,000′. Ridgetop winds are expected to remain from the North and West in the 15-25mph range with stronger gusts.  

For Sunday, sunny and cold weather remain. The one change could be another pulse of stronger Northerly winds. This blocking pattern of high pressure over Alaska looks to remain for the rest of the week. Keep tabs on what the NWS is finding at the bottom of their Forecast Discussion – Long Term Forecast!

PRECIPITATION 24-hour data (6am – 6am)

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 10   0   0   63  
Summit Lake (1400′) 9   0   0   29  
Alyeska Mid (1700′) 12   0   0   58  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 6   NW   10   31  
Seattle Ridge (2400′) 10   NW   10   34  
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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.