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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sun, March 3rd, 2013 - 7:00AM
Expires
Mon, March 4th, 2013 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

We have a MODERATE avalanche danger today for wind slab avalanches above treeline and persistent slab avalanches below treeline. An increase in easterly wind is expected to load upper elevation south and west aspects. Areas of most concern will be near ridgelines, rollovers and cross-loaded gullies. Additionally, below 3,000′ in the Placer Valley, 20-Mile, Grandview and Summit Lake regions various weak layers exist 2-6′ below the surface. There is the possibility a person could trigger one of these weak layers that results in a larger and more dangerous avalanche.

Sun, March 3rd, 2013
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.
Avalanche Problem 1
  • Wind Slabs
    Wind Slabs
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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

Wind slab avalanches will be our primary concern today as ridgetop winds have increased overnight. These are blowing steady at 15-20mph from the east and should continue through the day. Though the wind did kick up two nights ago creating shallow slabs and wind crusts, there still remains plenty of loose snow on the surface to be blown into new slabs and drifts today. Watching for winds actively loading slopes along with stiff and hollow feeling snow that may crack around you will be your best clues to avoid triggering a wind slab.

Additional Concerns:

Cornices – Cornices have grown steadily the past few storms and though several have fallen many are still looming. Avoiding these from both above and below will be prudent.

Loose snow avalanches – Sluffs should be fairly easy to initiate on steeper slopes sheltered from the wind again today. Scattered wind crusts and southerly aspects that may have a thin sun crust should help to limit sluffs.

Recent avalanche activity:
Yesterday’s sunny Saturday was not missed by many. Several folks were out enjoying the powder with human triggered avalanche activity confined to shallow (4-8″) wind slabs and loose snow sluffing. Natural activity came in the form of cornice falls and sun induced point releases on southerly aspects. There was one very large cornice that fell midday yesterday onto the south face of Magnum Ridge (image below). This backcountry bomb did trigger a few slabs on the way down that look to be mainly in the recent 3′ of storm snow. Right under the cornice it was scoured to the rocks and may have pulled out a couple pockets of snow breaking near the ground. More footage of this can be found HERE.

Avalanche Problem 2
  • Persistent Slabs
    Persistent Slabs
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
More info at Avalanche.org

There exist a few layers of concern buried several feet below the surface that we continue to mention. The first one involves various facet/crust combinations below 3,000’. We have not seen any avalanche activity on these layers in the Turnagain Pass region but they are suspect in the Placer Valley, 20-Mile, Grandview and Summit Lake areas (below 3,000’). The second layer of concern deals with weak snow near the ground in areas with a shallow snow cover. This problem is mainly confined to the mountains of the interior Kenai. Triggering an avalanche that breaks at one of these buried weaknesses is more of an outlier event but could be quite large. Safe travel practices, including limiting exposure time in avalanche paths and runnout zones, is a good way maximize a safe day playing in the backcountry.

 

Weather
Sun, March 3rd, 2013

Yesterday’s stellar day of blue skies, light east wind and temps in the upper 20’s has given way to high clouds overnight. These are associated with a low pressure system centered south of the Aleutians that will be skirting us to the south. Light snowfall has begun to fall in a few areas and ridgetop winds have bumped up from the east averaging 15-20mph with gusts to 40mph. Temperatures are holding steady around 20F on the ridgelines and 30F at sea level.

Today we can expect light snowfall to continue but is only expected to add up to an inch or so. Winds are likely to remain moderate from the east €“ averaging 15-20mph with gusts to 40mph. Temperature should stay in the mid 20’sF on the ridgetops but rise a bit at sea level to the mid 30’s where a spitting rain/snow mix is expected.

Tomorrow this system will continue to the southeast and we should see winds decrease and shift to more of a southwest direction. There is a chance for flurries tomorrow but partly cloudy skies with decent visibility is possible too.


Fitz will issue the next advisory tomorrow morning, March 4th.

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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.