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Issued
Sun, March 10th, 2013 - 7:00AM
Expires
Mon, March 11th, 2013 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

Many areas today will have a generally LOW avalanche danger. Pockets of MODERATE danger can be found above treeline where lingering wind slabs 1-2′ thick and large cornices remain possible for a person to trigger. These areas are most pronounced on slopes approaching 40 degrees and steeper as well as in the Girdwood Valley where significantly more snow fell Thursday and Friday. If skies clear enough today, watch for sun induced wet loose avalanches on southerly aspects.

Sun, March 10th, 2013
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
  • 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

Today’s shift to daylight savings time 2013 is accompanied by over 11 hours of daylight along with some variable snow surface conditions. The strong easterly winds during the end of last week’s storm did a little bit of damage in the Turnagain Pass zone. Everything from scoured surfaces to soft wind drifts up to 2’ deep to punchy wind crusts are out there. But don’t despair – there is still plenty of good settled powder in areas that escaped the brunt of the wind. Above 1,000′ that is. Below 1,000′, crusty melt-freeze conditions are firmly in place. It seems there was very little avalanche activity from the past storm event and mostly confined to cornice falls.

We found a few wind loaded slopes yesterday that showed signs of propagation and potential sensitivity to human triggers. Though no avalanche activity was seen or reported yesterday, these lingering slabs are a bit slow to bond and should be treated as suspect on steeper slopes – those approaching 40 degrees and steeper. As for the winds today, these are not forecast to be strong enough to move snow around. But in the case the disturbance over us intensifies and wind does increases, keep an eye out for any fresh wind drifts to form. Watching for cracking in the snow around you, along with stiffer snow over softer snow, will be your best clues for sussing out an old or new slab.

The Girdwood Valley received more than double the amount of snow at the end of last week than Turnagain Pass (28+” compared to ~12”). Hence, expect slabs in this region to be larger.

Additional Concerns:
Wet loose snow avalanches:  It’s that time of year. Watch for daytime heating, either by the sun or warm cloudy conditions, to dampen the surface snow. Roller balls are typically the first sign the surface is loosening and damp or wet sluffs become possible.

Avalanche Problem 2
  • Cornice
    Cornice
Cornice
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
More info at Avalanche.org

Once again, cornice falls make up one of the top two avalanche “Concerns”. These have grown to be very large in many areas. The past two storms were ideal cornice builders – characterized by mild temperatures and moderate to strong winds. Though Thursday saw 100+mph winds – too strong for good cornice growth – the majority of the snow came in after that, when wind had slackened to the 50mph range. Remember, cornices can release spontaneously just as easy as they can be triggered by a person, or several people, on ridgelines. Giving these guys a wider berth than thought necessary and steering clear of areas underneath them, especially during the heat of the day, will be wise.

Weather
Sun, March 10th, 2013

Yesterday’s chance for precipitation was denied and we have had no new snow in the past 24 hours. The sun broke through the clouds off and on throughout the day and winds were light from the southeast averaging ~10mph. Temperatures have remained in the low 20’s on the ridgetops and mid 30’s at sea level.

Today, a low pressure centered over western Alaska will push to the southeast and usher clouds over our area. We can expect a chance for a trace to an inch of snow. Winds are currently light and variable and look to pick up on the ridges to the 10-15mph range from the southeast. Temperatures look to remain around 20F on the ridgelines and mid 30’s at sea level.

A ridge of high pressure is forecast to build over the Bering for the early part of this week. This should bring clear skies and mostly light northeast winds with slightly cooler temperatures.


 Fitz will issue the next advisory tomorrow morning, March 11th.

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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.