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Issued
Tue, December 27th, 2011 - 7:00AM
Expires
Wed, December 28th, 2011 - 7:00AM
Forecaster
Graham Predeger
Avalanche risk The Bottom Line

Good morning. This is Graham Predeger with the Chugach National Forest Avalanche Information Center on Tuesday, December 27th at 7am. This will serve as 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).

BOTTOM LINE

There is a MODERATE avalanche danger today for wind slab and soft slab avalanches. Light density snow over the last few days coupled with light to moderate winds have loaded leeward slopes and the sides of gullies in mid and upper elevations within the forecast area. Human triggered avalanches are possible in steep wind loaded terrain. Natural avalanches are unlikely today.

AVALANCHE DISCUSSION

Yesterday proved anCNFAIC Staff quiet day in the backcountry. AnCNFAIC Staff 2-4 inches of light density snow fell within the Turnagain Pass area behind the moderate winds experienced on Christmas day. This light density snow we have experienced over the last several days does not require much wind for transport, thus stripping wind exposed slopes and creating tender cornices and shallow wind slabs on steep rollovers and gullies. Yesterday, the wind loaded slopes were found on south and west aspects above 2800 feet, this is also where the best skiing and snowmachining was found. If you do get a wind pocket to rip out, it will likely be small and shallow. However, going for a ride on a shallow wind slab can prove costly if you find yourself in steep, complex terrain and/ or above a terrain trap.

Temperatures stayed in the single digits all day yesterday and are slowly climbing into the teens this morning where we are expected to top out. These colder temperatures make for great powder skiing but effectively slow down the bonding process within the snowpack. What snow is falling and blowing around to form these soft wind slabs is taking more time to strengthen. This is a good example of the Betty Crocker principle. Think about a plate of chips and cheese in the oven. At a higher temperature (350 degrees) your cheese will bond to your chips in a matter of minutes and you will have delicious nachos. If the oven is only 100 degrees you will still make nachos, it will just take much longer to form that solid bond between chip and cheese. Now back to the snowpack; these fresh wind drifts from Sunday and minimal new snow from Monday are likely not bonded yet to the underlying new/ old snow interface. Warmer temperatures or time will be what is required to strengthen these bonds.

Watch out for any cracking or collapsing in the snow around you today, especially at upper elevations. This will be indicative that you have ventured onto one of these poorly bonded wind slabs and it may avalanche if the terrain is steep enough.

Generally, at and below treeline where wind effect has been minimal we are experiencing a right side up snowpack that continues to strengthen over time. Lower elevation test pits (<2500 feet) show a linear density profile from top to bottom, no persistent weak layers and overall rounding and sintering of grains. With relatively stable conditions in the backcountry, now is NOT the time to let your guard down. Continue to practice safe travel techniques and hone your rescue skills. Travel with competent partners, ski or high-mark slopes one at a time and always keep in mind your escape routes and safety zones.

MOUNTAIN WEATHER

Skiers and snowmachiners experienced cold temperatures and generally light winds and snowfall yesterday in the Turnagain pass area. As the low pressure system in the gulf moved through, we saw winds change direction from northeast to north to west at the Sunburst weather station as wind speeds diminished throughout the day. Overnight, this dominant low pressure system bottomed out at 960mb as it moved east of the forecast area. The core advisory area picked up an additional couple inches of snowfall yesterday afternoon/ evening.

Today, expect mostly cloudy skies and intermittent snow showers as the low pressure system in our region falls apart. Temperatures are slowly climbing up from the single digits and will likely top out in the teens or low 20’s. Expect a chance for an additional inch or two of light snow through the day. Winds are forecast to pick up to 15-30mph from the southeast. Our next best chance of moisture will arrive with a low pressure that is tracking toward the Gulf tomorrow. Models are showing this storm could take up residence in the Prince William Sound area by Wednesday evening, lingering into the weekend.

CNFAIC Weather Page and the NWS forecast

Kevin will issue the next advisory Wednesday morning. If you get out in the backcountry we want to know what you are seeing. Please send us your observations using the button at the top of this page or give us a call at 754-2369. Thanks and have a great day.

Tue, December 27th, 2011
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.
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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.