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ARCHIVED - Forecasts expire after 24 hours.
Issued
Tue, March 18th, 2014 - 7:00AM
Expires
Wed, March 19th, 2014 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

There is a MODERATE avalanche danger on all aspects and elevations above 2,000′. The possibility remains for a person, group of people or snowmachine to trigger a large, 3-5+’ deep, and destructive slab avalanche. Areas of most concern are steep slopes that have seen prior wind loading. Areas of most concern for triggering are shallow zones, commonly near rocks and the tops of rollovers.

Below 2,000′ the danger is generally LOW. At these lower elevations triggering an avalanche will be unlikely.  

Note: Not all MODERATE dangers are created equal. The ‘Avalanche Problem’ we have today is Deep Slab and with that a MODERATE danger means the chances are you won’t trigger an avalanche, but if you do it is likely to be unsurvivable. This is the ‘low likelihood – high consequence’ conundrum and something that deserves our respect.

Tue, March 18th, 2014
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
1 - Low
Avalanche risk
Below Treeline
Below 1,000'
1 - Low
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.
Avalanche Problem 1
  • Deep Persistent Slabs
    Deep Persistent Slabs
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.
More info at Avalanche.org

Once again, the main concern boils down to how our snowpack is adjusting to last week’s 3-5′ of heavy storm snow. The good news is, all signs for the past couple days have pointed to the new snow/old snow interface (3-5′ slab over weak preexisting snow) gaining strength. Though this is great news, it’s not something to completely hang a hat on, yet. It was only 3 days ago now that we had good enough visibility for folks to test the slopes and come away with a handful of human triggered large – and dangerous – avalanches. Also, we are still only 4 days out from the end of the storm itself. A bit more time to really let the snowpack prove innocent is warranted.

Though the likelihood of triggering a deep slab continues to decrease, the size of a potential slide remains large. Due to the high consequences, conservative terrain choices remain the best way to manage the problem. This means avoiding steep slopes, especially those with prior wind loading, and likely trigger points.  Likely trigger points include shallow spots in the snowpack and steep rollovers. For those with a higher risk tolerance, safe travel practices are key in avalanche terrain – this includes only exposing one person at time and keeping a close eye on your partners.

*Areas that have a higher likelihood are places that did not receive as much snowfall from last week’s storm and have a shallower overall snowpack. For example the central Kenai – Palmer Creek area, Silvertip region and Summit Lake zones.

Avalanche Problem 2
  • Dry Loose
    Dry Loose
Dry Loose
Dry Loose avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.
More info at Avalanche.org

By the look of the satellite imagery this morning, the sun may shine more than expected today. Also, the winds are slated to be calm to very light. These factors combined can create significant warming at the snow surface. If this is the case today, watch for damp to wet loose avalanches on southerly aspects. These would likely just entrain the light 3-5″ of snow from Sunday.

Weather
Tue, March 18th, 2014

It was one of those overcast and low visibility days yesterday. Light snow showers were off and on but only added a trace of snow. Temperatures during the past 24-hours have averaged in the upper teens on the ridge tops and winds have been light, 5-10mph, from the East.

Today, we may see a few snowflakes before skies begin to clear. Temperatures are expected to climb to the low 30’sF at 1,000′ and around 20F on the ridgelines. Winds look to shift to the NW this morning and remain light, around 5mph, before picking up to the 20mph range late tonight.

Mostly clear skies and mild temperatures are on tap for Wednesday and Thursday as high pressure builds over mainland Alaska. This high looks to persist into the weekend.  

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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.