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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sat, March 2nd, 2013 - 7:00AM
Expires
Sun, March 3rd, 2013 - 7:00AM
Forecaster
John Fitzgerald
Avalanche risk The Bottom Line

The avalanche hazard is MODERATE above and below treeline.   Above treeline loose unconsolidated snow will be easy to trigger in steep terrain, especially on sunlit aspects.   At the mid and lower elevations the potential exists to trigger isolated pockets of slab 1-3′ deep.   The hazard will rise as warm temperatures and sunshine will make it easier to initiate avalanches today.

Sat, March 2nd, 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. 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
  • Dry Loose
    Dry Loose
Dry Loose
Dry Loose avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.
More info at Avalanche.org

Today watch for steep sunlit slopes to be the most likely place to trigger a loose snow avalanche.  Expect sluffs to become wet and increase in volume with the presence of sunshine and higher temps.  Yesterday my partner and I observed several natural loose snow avalanches in terrain over 40 degrees and we were able to initiate sluffs in this terrain as well.  Expect similar activity today and make sure that you are aware of the terrain below you.  If you see loose snow moving downhill with you or in front of you steer away from it at a gradual angle before it knocks you over.  Getting knocked down by these avalanches will have greater consequences when a person is above terrain traps such as cliffbands, gullies, or trees.  

 

Additional Concerns

Wind Slabs
Winds have been generally light over the past 24 hours.  There was a 4 hour window last night where Easterly winds increased enough to create new shallow wind slabs.  Older wind slabs formed during the past week are less likely to be an issue today.  Nonetheless, it is worth avoiding steep terrain where the combination of loose snow and isolated pockets of wind slab will be enough to knock you off of your feet or snowmachine.

Cornices

Sun and warming will increase the chances of cornices breaking and dropping onto slopes today.  Give cornices a wide berth from below and above, as they can do a lot of damage to a person.

Avalanche Problem 2
  • 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

The storms of the past week have put down 2-3 feet of “new” snow that is sitting on a crust.  In some areas weak snow sits on top of this crust that exists between ~1,500-3,000′.  Snowpit tests yesterday did not show this interface to be a serious concern on Turnagain Pass.  That could change today, as warm temperatures and sunshine will make it easier to trigger deeper avalanches on steep lower elevation slopes, and areas where the newest slab is thinner.  Areas with less overall snow (e.g. heading south towards Summit Lake and lower elevations in general) are where it is worth paying more attention to this problem today.

Weather
Sat, March 2nd, 2013

The mountains around Eastern Turnagain Arm have picked up 2″ of new snow containing .1″ of water in the past 24 hours.   Winds have been generally light out of the E and SE averaging 8mph with gusts as high as 36mph.   Temperatures at 3,800′ have averaged 18 degrees F and 25 degrees at 1,880′.

Today expect a mild and calm day in the mountains.   Sunshine and warm temps will be the most important weather factors today in terms of avalanche activity.   Expect periods of clear skies and temperatures to be in the high 30s at 1,000′.   Ridgetop winds will be light, coming out of the SE at 5-10mph.

The extended outlook calls for a mix of sun and clouds over the next several days with only a slight chance of snow.

___________________________________________________________________

Wendy will issue the next advisory tomorrow morning, March 3rd.

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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.