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Issued
Mon, February 27th, 2012 - 7:00AM
Expires
Tue, February 28th, 2012 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

Good morning. This is Wendy Wagner with the Chugach National Forest Avalanche Information Center on Monday, February 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).

ANNOUNCEMENTS

Alaska DOT crews will be conducting avalanche mitigation work along the Seward Highway. Intermittent road closures are possible – check 511.alaska.gov for more information.

BOTTOM LINE

The avalanche danger remains CONSIDERABLE for storm snow instabilities with continued snowfall. Dangerous wind slab avalanches are likely to be triggered on steep slopes with recent wind deposited snow above treeline. Additionally, loose snow avalanches will be likely and soft slab avalanches will be possible to trigger at all elevations on slopes greater than 35 degrees. Conservative travel is recommended today.

AVALANCHE DISCUSSION

By yesterday afternoon, Sunday’s storm had laid down 8-14 inches of new snow with moderate to strong easterly winds. As of this morning, the wind has decreased but snow is still falling. Storm totals are now hovering between 1 and 2 feet – slightly more in the Girdwood Valley and less at Summit Lake. The extent of natural avalanche activity yesterday was shrouded in the clouds, as usual, but people were able to trigger pockets of fresh wind slabs on steep rollovers near treeline.

The new snow came in on top of several inches of very loose powder containing large sharp crystals and initial bonding was poor (further details and video HERE). Along with the poor bonding, increasing temperatures and/or wind allowed the new snow to become cohesive and act as a slab. This weak snow under the new slab made for easy cracking and small avalanches on steep short test slopes near and below treeline. It is a fairly easy bet that areas above treeline, with significantly more wind, were quite sensitive.

Today this bonding with the old snow, as well within the new snow from overnight, is the big question. It is likely ‘settling’ out and slabs will not be as easy to trigger at and below treeline. There, of course, is uncertainty with how quickly the increase in stability will be above treeline.

Above treeline:

Wind slabs that are sitting on loose weak snow is today’s primary concern. The winds have died down dramatically this morning but light snow continues which can cover the visual clues as to where they lie. Conservative travel above treeline (e.g., keeping slope angles low) is recommended today as these slabs may be strong enough to allow a person to get well onto the slope before it releases making escape difficult and consequences unpleasant.

All elevations:

Loose snow avalanches are expected to be easy to initiate with the continued new snow. As is the key with these, keep an eye on where your sluff runs. It may also be possible that these sluffs could pull out a wind slab lurking below.

Soft slab avalanches may be less likely today but still possible to trigger on steeper rollovers in areas without much wind. These could fail both on the older snow creating a deeper avalanche, or within a change in density within the new snow for a shallower avalanche.

Cornices continue to grow and teeter on the brink of failure. Check out the updated pictures and observation sent in yesterday.

MOUNTAIN WEATHER

The storm that rolled through yesterday laid down a healthy dose of medium density snow. As of this morning, estimated totals are:

Turnagain Pass are 14-20″

Girdwood Valley 20-25″

Summit Lake 8-12″

Easterly winds accompanied the new snow and averaged around 35mph with gusts up to 60mph. The wind has shifted early this morning and has died down where it should remain light from a northerly direction. Light snow will continue to fall through the day adding anCNFAIC Staff 3-5 inches (with possibly more) of lower density snow. Temperatures warmed through the storm yesterday but have begun a slight decrease this morning where they sit at the mid 20’s at 2000′ and the upper teens at 4000′.

CNFAIC Weather Page and the NWS forecast

Graham will issue the next advisory Tuesday 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.

Mon, February 27th, 2012
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
3 - Considerable
Avalanche risk
Below Treeline
Below 1,000'
3 - Considerable
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. Dangerous avalanche conditions. 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.