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ARCHIVED - Forecasts expire after 24 hours.
Issued
Tue, March 20th, 2012 - 7:00AM
Expires
Wed, March 21st, 2012 - 7:00AM
Forecaster
CNFAIC Staff
Avalanche risk The Bottom Line

Good morning. This is Chris Engelhardt with the Chugach National Forest Avalanche Information Center on Tuesday, March 20th 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

Above tree line there is a MODERATE avalanche danger concerning a variety of buried persistent layers. There also could be pockets of CONSIDERABLE danger for significant loose snow sluffing and point releases on south and sunny aspects today if things really warm up. Below tree line the danger is generally LOW, except for steep rolls and convexities where buried sun crusts and surface hoar may exist.

Continue to be heads up in the Placer Valley, Twentymile and Johnson Pass areas for triggering slab avalanches on buried surface hoar.

AVALANCHE DISCUSSION

The open alpine terrain was pretty well obscured yesterday and observations were limited for the higher elevations. We were relegated to below tree line terrain where the new, 6-10” of super light density snow made for blower conditions. We checked out a variety of aspects, SW, W and N through NE/NW and found the new snow to be virtually shooting down the hillside rapidly on anything steeper than 35degrees. We attributed this to its very light density, but its velocity could also have been increased due to its laying on widespread surface hoar on the old snow surface. Also, a beefy new suncrust formed on the south aspect during the past weekend adding yet anCNFAIC Staff bad layer not only for skiing, but for stability on the south aspect.

Concern #1: Loose snow & Wet Loose Activity

If the day develops into being sunny and clear with warming temperatures there will be wet loose natural activity on south and sunny aspects. The new snow will easily sluff off this weekend’s suncrusts and surface hoar and will be actively shedding from cliffs and steeper areas. Avoid skiing or snow machining on or underneath terrain that is getting direct solar radiation and heat. Also, expect very reactive and quickly moving sluffs on all aspects when skiing/riding today.

Concern #2: Buried Surface Hoar

The new surface hoar had been widely seen before yesterday’s new snow, check out these observations HERE and HERE). It has been widely observed on all aspects and elevations.

We also know that a surface hoar layer developed previously before last week’s big 2-3 foot snow fall and is lurking on variable aspects and elevations. This older surface hoar layer was very reactive and triggered numerous slides around the Placer drainage at the end of last week, but it has been harder to find and identify in the Turnagain Pass Zone. This being said, it remains a concern and is definitely something to look for as you perform future test pits.

Concern #3: Buried Sun Crust

An old suncrust around 2 feet below the surface still resides on most sunny aspects. Yesterday, we were able to get fairly easy to moderate failures with clean planer shears on this layer in test pits. This layer could provide a deeper trigger point on south aspects if you would hit the “sweet spot”. Also anCNFAIC Staff suncrust formed this past weekend and proved to be a great sliding surface for yesterday’s new snow, it also proved to provide horrible breakable crust for making turns.

MOUNTAIN WEATHER

Yesterday we found 6-10” of new light density snow at Turnagain Pass. Winds were very light and temps were fairly warm 25-30F at 2000ft elevation. It snowed steadily and was coming straight down throughout midday. We saw that it was snowing over an inch an hour around 100pm when we returned up our skin track to check out a different aspect. Winds remained very light overnight 7-12mph and were swirling from all directions. Temperatures hovered around the mid-teens at ridgetops and more than likely it continued to snow a decent amount yesterday evening at the pass.

Today, a chance for snow showers exists with partly cloudy to sunny conditions and warm temperatures at lower elevations. If these sunny and warm conditions do prevail today backcountry travelers will need to be real aware of staying away from warming sunny aspects.

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 20th, 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. 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.