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ARCHIVED - Forecasts expire after 24 hours.
Issued
Fri, March 6th, 2015 - 7:00AM
Expires
Sat, March 7th, 2015 - 7:00AM
Forecaster
Heather Thamm
Avalanche risk The Bottom Line

Much of the terrain in Turnagain Pass has a LOW danger where triggering an avalanche is unlikely. However there are areas in the Alpine, above 2500′, where the avalanche danger is MODERATE and triggering a slab 1-2′ is possible. This will be more likely in steep complex terrain, like on large unsupported slopes, around steep rocky features and in steep gullies.  

Special Announcements

Tonight at Midnight Sun Brewery from 5-7:30pm, The White Out Gallery and 19 very talented and generous Alaskan artists have come together to host a month long art show and auction, as a fundraiser for the Alaska Avalanche School. The funds will go to the Know Before You Go youth education program and the Instructor Development Fund.

Fri, March 6th, 2015
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
1 - Low
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
  • 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

In the Alpine a slab 1-2′ thick is sitting on a old weak layer of snow, but over the last 10 days triggering this slab has become more difficult with time. Very few obvious signs of instability have been observed over the last week, and inconsistent test results help point towards this weak layer adjusting to its load. On the flip side, we are still finding propagation potential in places, causing enough uncertainty to still encourage conservative slope choices. This problem seems to be more reactive on slopes with more of a Southern aspect where a sun crust/facet interface exists.

Obvious clues such as collapsing/woomphing may not be present and triggering a slab may require steeper terrain or a larger trigger, like several people on a slope. Be sure to practice safe travel habits. Identify safe spots, move between islands of safety one at a time, and always have an escape zone in mind.

Overnight only a trace of new snow fell in Turnagain Pass above 2000’ and another wave of precipitation is expected tonight into Saturday morning. Unfortunately for Turnagain Pass the direction of this cold front looks to be favoring the Talkeetna Mountains. If heading to Hatcher Pass this weekend, be sure to check out the Hatcher Pass Advisory updated once per week on Saturday mornings. 

A stout melt/freeze crust has strengthened the snow pack below 2500’ and has been providing spring-like surface conditions below this elevation. 

Snow may be scarce below 1500′, but a good time can still be found in the the upper elevations.  

Avalanche Problem 2
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

 

 

Additional Concern
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

Yesterday cloudy skies slowly broke in the morning and by mid-day it was mostly sunny. Temperatures reached the mid 30’s F during the heat of the day, just enough to cause some melting in the 1-2” of new surface snow on sun exposed aspects. Along ridgetops winds were light (5-15mph) mostly from the East.

Overnight temps dipped into the high 20’s F along ridgetops, but at sea level temperatures remained above freezing. There was light rain overnight with rain/snow line around 2000’, up to a few inches of new snow above 2000’. Winds were variable in Turnagain Pass, with Sunburst experiencing a Southerly direction 10-20mph, and Seattle with light Northeasterly winds 5-10mph. 

Tonight another wave of precipitation is expected to move through Western Prince William Sound bringing up to a few inches of snow to upper elevations. Rain/snow line will be around 1000’, with temperatures cooling off late Saturday afternoon as precipitation backs off. Southeast winds are expected to be 20-30mph.  

Weather
Fri, March 6th, 2015

Yesterday cloudy skies slowly broke in the morning and by mid-day it was mostly sunny. Temperatures reached the mid 30’s F during the heat of the day, just enough to cause some melting in the 1-2 € of new surface snow on sun exposed aspects. Along ridgetops winds were light (5-15mph) mostly from the East.

Overnight temps dipped into the high 20’s F along ridgetops, but at sea level temperatures remained above freezing. There was light rain overnight with rain/snow line around 2000′, up to a few inches of new snow above 2000′. Winds were variable in Turnagain Pass, with Sunburst experiencing a Southerly direction 10-20mph, and Seattle with light Northeasterly winds 5-10mph.  

Tonight another wave of precipitation is expected to move through Southcentral Alaska bringing up to a few inches of snow to upper elevations. Rain/snow line will be around 1000′, with temperatures cooling off late Saturday afternoon as precipitation backs off. Southeast winds are expected to be 20-30mph.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 35   0   .1   40  
Summit Lake (1400′) 35   0   .1   7  
Alyeska Mid (1700′) 35   0   .14   24  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 28   Var.   12   27  
Seattle Ridge (2400′) 29   NE   11    15
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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.