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ARCHIVED - Forecasts expire after 24 hours.
Issued
Thu, January 23rd, 2014 - 7:00AM
Expires
Fri, January 24th, 2014 - 7:00AM
Forecaster
Kevin Wright
Avalanche risk The Bottom Line

Rain…

The unusually warm and long lasting rain event continues today.  Dangerous avalanche conditions are the new normal until this storm system ceases and temperatures get below freezing.  Specific areas may reach  HIGH avalanche danger during periods of intense precipitation.  

Natural avalanches are happening periodically during this continuing storm cycle.  Some of these are quite large.  

Thu, January 23rd, 2014
Alpine
Above 2,500'
4 - High
Avalanche risk
Treeline
1,000'-2,500'
4 - High
Avalanche risk
Below Treeline
Below 1,000'
4 - High
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.
Avalanche Problem 1
  • Wet Loose
    Wet Loose
Wet Loose
Wet Loose avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
More info at Avalanche.org

We continue to see new wet avalanche activity.  The big new one was on the west face of Cornbiscuit.  The lower part of the upper face pulled out full depth sometime between Tuesday night and Wednesday morning.  This area is above treeline but well within the zone that is getting rain.  See photo below.

As long as temperatures remain above freezing and especially during active rainfall, wet slab avalanches are possible and can be quite dangerous.  

Avalanche Problem 2
  • 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

Deep slab continues to be a concern as the upper elevations have stress added.  The equation here is simple – known reactive weak layers are getting heavy additional loading day after day.  These weak layers can cause large widespread avalanches anywhere from 4-7 feet deep and pull all the snow to the ground.  This problem is also worse during periods of precipitation, but will linger even after the storm ends.

Steep upper elevation terrain should be avoided, especially during periods of intense precipitation.  

Additional Concern
  • Storm Slabs
    Storm Slabs
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
More info at Avalanche.org

Up in the higher elevations there is enough storm snow and wind loading to have problems in the recent layers.  Think about wind slabs and storm slabs 1-3 feet in depth.  If an avalanche is started in these layers it could possibly step down into deeper layers.  I will be surprised if anybody actually makes it above the rain line today.

Weather
Thu, January 23rd, 2014

A steady jet of moisture is coming from subtropical latitudes, straight north to southcentral Alaska.  This pattern is expected to persist through Friday night.  According to the National Weather Service, the Eastern Kenai peninsula could get another 3-6 inches of rain through Friday afternoon.  Freezing levels will also increase to 4000-6000 feet elevation.  

Today looks like the warmest yet.  Rain will continue, transitioning to snow around 2400 feet.  Wind at the ridge tops – Southeast 28-40 mph.  

The first sign of a break from this pattern is on Saturday, with a chance of partly sunny skies.

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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.