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ARCHIVED - Forecasts expire after 24 hours.
Issued
Tue, March 6th, 2012 - 7:00AM
Expires
Wed, March 7th, 2012 - 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, March 6th 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

Below tree line and in areas where wind has not affected the snow surface the avalanche danger is generally LOW. Above tree line in wind-affected areas the danger is MODERATE for fresh and tender wind slabs building in the wake of yesterdays weak low-pressure system. Additional concerns today come in the form of skier-triggered sluffs and wet point release avalanches as we can expect some solar influence this afternoon.

AVALANCHE DISCUSSION

The stoke was high this past weekend with lots of people getting out to enjoy the mountains and our ample snowpack. Avalanche activity over the last several days has been relegated to surface instabilities in the form of wet point releases on sun affected slopes, human triggered dry sluffs and shallow soft slabs.

Today we can add to this the possibility of wind slab avalanches. Winds picked up yesterday afternoon in the moderate range as most folks were just leaving the backcountry. Light and dry surface conditions meant there was plenty of snow available for transport. We can expect that wind slabs formed overnight and are ripe for a trigger in the form of a skier or snowmachiner today. The most likely areas to find tender wind slabs will be above tree line; below ridges and steep rollovers as well as on cross-loaded slopes. Winds have been predominantly from the east and southeast so expect north and west slopes to be especially touchy today. These slabs are forming on loose, unconsolidated snow setting up a classic strong (wind slab) over weak (loose snow) scenario conducive to avalanching. These will most likely be relatively shallow but there is always the possibility of a wind slab to step down into deeper layers.

Secondary concerns continue to be loose snow avalanches in the form of skier-triggered sluffs. Sluffing has been very prevalent on steeper slopes (greater than 38 degrees) given the loose surface conditions. Sluffs have the potential to entrain a significant amount of snow and may be enough to rip out shallow soft slab avalanches as our test results yielded yesterday (ECTN27, RB5) within the top two feet of our snowpack.

Moreover, as we continue into spring the sun is bound to play an increasing role in our snowpack instabilities. Today and for the remainder of the avalanche season pay attention to moistening surface conditions (especially on south and west aspects) and CNFAIC Staff clues such as roller balls or wet point release avalanches. These are all signs that solar radiation is at play and may provide just enough energy to tip the balance.

MOUNTAIN WEATHER

Sunday’s mostly clear skies and cold overnight temperatures gave way to clouds yesterday with the approach of a weak low-pressure system that scoured the cold air from low lying areas and shrouded our visibility in the Turnagain pass area. Wind and snow moved into the Girdwood and Turnagain pass areas later yesterday afternoon with an overall rise in temperature. Snowfall was generally modest with about 6″ falling across our forecast area overnight.

Today we can expect high clouds and light snow to give way to clearing skies as yesterday’s weak low-pressure system moves out. As snow showers end today, drier weather will dominate the south-central region for a day or two before the next weather producing system rolls in later this week. Winds will be light out of the northwest today with temperatures in the 20’s at 1000′.

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, March 6th, 2012
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.