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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sat, March 30th, 2013 - 7:00AM
Expires
Sun, March 31st, 2013 - 7:00AM
Forecaster
Kevin Wright
Avalanche risk The Bottom Line

Yesterday snowed most of the day, with precipitation shutting off around 9pm last night.  Up to a foot of new snow accumulated in some higher elevation areas with a moderate southeast wind.  Above treeline a  MODERATE  avalanche danger can be found for wind slab created during the last 2 days.  Pockets of unstable snow can be found today, but are generally isolated to wind loaded features.

Skiers and riders in the backcountry today should be wary of stiffer snow on steeper terrain.  Non-wind affected areas will be less of a concern.

Special Announcements

This Sunday is the  2nd  ANNUAL  CORN HARVEST  – get it on your calendar now !! Come join the CNFAIC Friends and Forecasting staff on Turnagain Pass for  FREE FOOD, games, prizes, etc. This is one way we would like to thank all of you for your dedication and support.

Sat, March 30th, 2013
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

Nearly all the activity we’ve seen recently can be classified under wind slab.  Fortunately everything we’ve seen has been low volume and isolated to small pockets.  The photo below is from 2 days ago on Tincan.

Since we just got a significant additional load of new snow and wind, this concern is worse today.  Snowfall was heavy enough yesterday to limit visibility and prevent anybody from getting above treeline.  We haven’t seen firsthand the areas of highest concern, but we know it’s been snowing and blowing.  

South facing slopes will add another layer of complexity.  Multiple layers of buried sun crusts can be found on sunny aspects.  We don’t know how those layers will react to the moderate additional snow load, but it’s worth considering that new snow doesn’t bond easily to slippery crusts.  Stability aside, those crust layers may affect the quality of skiing and riding on south aspects.

 

Avalanche Problem 2
  • 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

In areas that were not wind affected we can expect loose snow to sluff easily in steep terrain.  Anywhere the wind didn’t stiffen up the surface and slope angles exceed the mid 30 degrees you should expect snow to sluff and entrain volume on the way down.  This could be a problem if surprised or in steep channeled terrain.  

Weather
Sat, March 30th, 2013

Snow totals for the last 24 hours

Turnagain Pass snotel – 8 inches

Alyeska midway – 10 inches

Summit lake mountains – 6 inches

Wind has been trending from the southeast in Turnagain Pass with variations depending on the location.  Temperatures are warmer than they’ve been, producing mixed rain and snow at sea level.  Above 1500 feet the snow is dry.

Today’s weather calls for scattered snow showers.  The bulk of the precipitation has passed.  Expect a slight cooling trend and a diminishing trend with the wind.  


Wendy will issue the next advisory tomorrow morning, March 31st.

Observations
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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.