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ARCHIVED - Forecasts expire after 24 hours.
Issued
Thu, December 12th, 2013 - 7:00AM
Expires
Fri, December 13th, 2013 - 7:00AM
Forecaster
Kevin Wright
Avalanche risk The Bottom Line

Avalanche danger is currently  LOW  in our region.  The big change in the last couple days is a dramatic drop in temperatures, with a change from above freezing to below freezing.  That action typically “locks” the snowpack in place until another change occurs.  

Thu, December 12th, 2013
Alpine
Above 2,500'
1 - Low
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
  • Normal Caution
    Normal Caution
Normal Caution
Normal Caution means triggering an avalanche is unlikely but not impossible.
More info at Avalanche.org

There is still visible evidence of loose snow “avalanche” activity from the last week.  In every case we’ve seen these have been low-volume point releases that occurred during the warm temperatures.  

Now, as temperatures have plummeted, a prominent melt/freeze ice crust should be expected everywhere on the snow surface.  This crust will be found at all elevations and all aspects.  It formed from freezing rain and above freezing temperatures between Dec 2-8.  We haven’t seen this crust to be strong enough to be supportable anywhere – the underlying snow is just too weak to provide strength under the crust.  This makes for very challenging mountain travel right now. 

That crust also has a surface hoar layer forming, adding to the complexity of our future bed surface.

Photo – Bob Sutherland – crust with surface hoar

Weather
Thu, December 12th, 2013

The temperature profile above is from the Seattle ridge weather station, showing a timeline from Dec 8 to the present.  This is the reason why we have the melt/freeze crust everywhere.  Current temperatures range from low single digits to the teens at some sea level locations.  

It hasn’t snowed in quite a while, making temperature swings and freezing rain the most interesting weather events over the last week.

The forecast discussion for Friday and Saturday is exciting!  “The upper air pattern shift is complete… and a surface low tracking into then stalling in Prince William Sound.”  “The bulk of accumulating snow comes Friday and Early Saturday.  Storm total accumulations for Anchorage and vicinity will generally range from 4 to 8 inches… but there is the potential for locally higher values.”

Read the entire discussion  HERE.  We can expect our snowpack stability to get dramatically worse with this new snowfall for the weekend, depending on how much we get.  Stay tuned and check back for the latest information.

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.