Turnagain Pass RSS

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ARCHIVED - Forecasts expire after 24 hours.
Issued
Fri, March 27th, 2015 - 7:00AM
Expires
Sat, March 28th, 2015 - 7:00AM
Forecaster
Heather Thamm
Avalanche risk The Bottom Line

Today the avalanche danger is MODERATE both in the Alpine and at Treeline. Triggering a wind slab up to 2′ thick is possible on steep sustained slopes. If the sun comes out today 1-2′ of newly fallen snow will be susceptible to rapid warming and could produce natural wet avalanches on Eastern and Southern slopes. It will be important to avoid large steep slopes and pay attention to surface conditions if the sun makes an appearance today.

Below treeline heavy wet snow conditions could make recovery out of a terrain trap difficult. Keep an eye out for steep gullies, open drainages and tree wells at this lower elevation band.

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Fri, March 27th, 2015
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
0 - No Rating
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

Yesterday 1-2′ of new snow fell in Alpine of Gridwood and Turnagain Pass and the most intense part of this storm occurred between 2am and Noon.  Ridgetop winds averaged in the mid 20’s mph from the Northeast with gusts into the high 40’s mph for a 24 hour period.

Storm snow totals are from the last 36 hours:

Turnagin Pass ≈ 1” of water (16” at 2800’)

Girdwood = 2.05” of water (21” at 2800’ at Alyeska)

Summit Lake ≈ 0.1 water (trace)

This new snow will likely gain strength quickly as it settles, but triggering a wind slab up to 2’ thick is possible on steep slopes. Surface conditions below this new snow are variable with a sun crust on Southern and Eastern aspects and pockets of weaker snow on Northern and Western slopes. Today it will be important to avoid large steep sustained slopes and give this new snow a chance to adjust to the variable bed surfaces below.  

 Moderate ridgetop winds yesterday were transporting snow in the Alpine. Photo taken at 3200′ on the ridgeline above Common Bowl,Tincan 

 

 

Avalanche Problem 2
  • Wet Loose
    Wet Loose
Wet Loose
Wet Loose avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
More info at Avalanche.org

Yesterday several loose snow ‘point releases’ and a small storm slabs were observed in steep terrain in Turnagain Pass. This new snow will be susceptible to rapid warming due to solar affect and could cause wet point releases and wet slabs if the sun makes an appearance. It will be important to monitor the sun’s affect today – even thin cloud cover could increase solar affect acting as a large reflector. Pay attention for moist surface conditions and avoid large steep slopes that will have more volume if an avalanche is triggered.

Small D1 point releases “sluffs” and a fresh storm slab on “CFR” on Tincan mid day during a brief window of good visibility. 

 

Day-time temperatures yesterday were warm and rain/snow line moved from 800’ in the morning to 1700’ in the afternoon. This caused a period of rapid melting below this elevation. Today wet loose avalanches on steep terrain features will be an additional hazard below treeline. 8-10” of heavy wet snow could be challenging to move through and early season conditions like open drainages and tree wells exist at this lower elevation band. Avoid terrain traps – it could be difficult to dig yourself out if caught up side down. 

Two photos taken yesterday of the same tree at 1600′.1st picture was taken at 11:30am and the second was taken at 4pm after rain/snow line moved to 1700′. Photo by John Fitzgerald.

 

 

Weather
Fri, March 27th, 2015

Total precipitation for Turnagain Pass was near an inch of water, which was a mix of rain and snow depending on elevation. Rain/snow line was at 800′ yesterday morning, but quickly moved to 1700′ by the afternoon. Temperatures at sea level were in the mid 30’s F to low 40’s F, and upper 20’s F at ridgetops. Ridgetop winds averaged in the 20’s mph with gusts into the high 40’s mph from the NE.

Today rain and snow showers are expected and patches of sun are possible. Rain/snow line will likely be near 2000′ today and up to 3 € could fall at higher elevations.   Temperatures will remain warm; high 30’s F at sea level and mid 20’s F along ridgetops. Ridgetop winds will be from the East, 10-20 mph.

A low pressure system South of the Alaska Peninsula will bring another burst of rain and snow to Southcentral Alaska over the weekend. This will continue to bring us warm moist air, rain near sea level and snow in the interior and in the Alpine. It is uncertain how much precip will fall. Winds will likely be moderate at times, 20-30 mph from the East along ridgetops.  

 *Seattle Ridge Wx Station is not producing accurate wind direction data at this time.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 34   5   0.4   60  
Summit Lake (1400′) 36   1   0.1   12  
Alyeska Mid (1700′) 34   1   0.89 32  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 26   ENE   23   49  
Seattle Ridge (2400′) 28   * 19   41  
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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.