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Issued
Sun, February 26th, 2012 - 7:00AM
Expires
Mon, February 27th, 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 Sunday, February 26th 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

The avalanche danger will rise to CONSIDERABLE today due to the onset of heavy snowfall and wind. Storm snow avalanches, in the form of loose snow, wind slab and soft slabs, will all be likely to be triggered by a person and natural avalanches are possible. It is a storm day and expert level route-finding and terrain management skills will be required for safe backcountry travel. (Remember there is a Sunday Summit Lake advisory.)

AVALANCHE DISCUSSION

It was a fairly busy Saturday at Turnagain Pass with several folks soaking up the sun in the morning until high clouds began moving in ahead of today’s storm. Those getting a close look at the snow surface may have noticed some very large stellar crystals on top shining in the sun. Avalanche activity that was seen/reported was confined to human triggered sluffs on the steeper slopes that initiated in, and entrained, the top several inches of loose powder. A few of these were medium sized and ran quite far. There was also a report of a large cornice break on the far end of Magnum ridge – report HERE.

The loose powder that was sluffing from our snowmachine or board(s) yesterday is now covered with 4-6 inches of new snow overnight, with anCNFAIC Staff 8-16 inches on tap. Bonding of the new snow with older loose snow (including those nice stellar crystals) will likely be poor initially – enhancing all avalanche activity through the storm. Furthermore, how the new snow will bond within itself will also be concern.

Wind slab avalanches – near and above treeline:

The current moderate to strong winds above treeline are, and will be, moving and depositing the new snow into slabs onto the leeward sides of slopes. These are most likely to form off ridgelines, over rollovers and cross-loading on the sides of gullies. Expect these to be quite sensitive, dangerous, and easy to trigger. It is possible to trigger one of these from the side or below with the poor bonding expected with the older snow.

Loose snow and soft slab avalanches – all elevations:

Sluffing in the new storm snow will be likely today, both human triggered and natural. Watch for these to run fast and far with the new and loose snow sitting on top of a harder sliding surface. Soft slabs are also possible today on all slopes at all elevations. Watch for the temperatures to increase. If this happens slightly denser new snow will fall over lighter new snow and slabs can pop out even in areas without wind.

MOUNTAIN WEATHER

High clouds moved in throughout the day yesterday, after a sunny morning, signaling the approach of a storm heading our way from the southwest. Winds were light from the east in most areas, but picked up on the northern end of Turnagain Pass where they were gusting near 20mph (This can be seen on the SEATTLE RIDGE weather station – which is now back up and running!). Temperatures were chilly, in the teens.

A large low pressure system in the Bering is currently pushing a front over our area now from the west and will continue to move easterly today. Overnight, around 4-6″ of snow has fallen on Turnagain Pass with similar amounts in both the Girdwood Valley and the Summit area. We can expect anCNFAIC Staff 8-16″ to fall through the day with close to 1” of water weight. Temperatures are expected to remain just cold enough, low 30’s, for snow at sea level and increase a few degrees from where they sit currently: 22F at 2000′ and the mid-teens 4000′. Easterly winds have picked up overnight and are averaging ~30mph with gusts between 40 and 50mph where they are forecast to remain.

CNFAIC Weather Page and the NWS forecast

I will issue the next advisory Monday 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.

Sun, February 26th, 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. 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.