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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sat, April 6th, 2013 - 7:00AM
Expires
Sun, April 7th, 2013 - 7:00AM
Forecaster
John Fitzgerald
Avalanche risk The Bottom Line

The avalanche hazard is LOW above and below treeline.   New snow amounts will be relatively light today.   However, shallow pockets of new slab will form and be easy to trigger in steep upper elevation terrain.   It is in these areas where the avalanche hazard will inch up to the MODERATE range very late in the day.

Sat, April 6th, 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. 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
  • 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

Small slabs will be easy to trigger by the end of our long day today (sunset will be at 9pm tonight).  Snowfall will pick up later in the day.  Prior to new snow falling it is always a good practice to know what the snow surface is comprised of.  Yesterday south facing and low elevation slopes melted during the day and froze overnight.  North facing slopes in the upper elevations were holding pockets of small surface hoar.  As this “drought layer” gets buried it will need to adjust to the new snow falling onto it.  Surface hoar will not allow new snow to bond to it very well.  Neither will crusts.  If the new snow comes in warm, as it is forecasted to do, bonding will be better.  Shallow wind slabs will build by this evening in isolated pockets and are worth avoiding on steep north through west facing aspects.

Avalanche Problem 2
  • Normal Caution
    Normal Caution
Normal Caution
Normal Caution means triggering an avalanche is unlikely but not impossible.
More info at Avalanche.org

While the snowpack is stable in many areas, there are a few things to consider today when making decisions.

Loose Snow Avalanches

Yesterday my partner and I found surface hoar on steep high elevation north facing slopes.  This surface will prevent new snow from sticking to it well.  Because of this, low volume sluffs will run fast and readily in this type of terrain.  While the volume will be too low to be a problem on its own, things can change for the worse when these small avalanches occur while you’re above cliffbands, gullies or trees.

 

Cornices

While today is not a prime day for cornices to come crashing down, it is still worth remaining vigilant in the presence of these large masses of snow.  Give them plenty of room when approaching ridgecrests and while travelling below them.

Weather
Sat, April 6th, 2013

In the past 24 hours the Sunburst weather station at 3,812′ reported an average temperature of 20 degrees F.   Winds were calm to light, blowing 4 mph out of the SW.   No measurable precip has fallen.

Light snow showers have begun this morning.   Today expect up to 6″ of new snow.   Ridgetop winds will be light out of the SE at 10-15mph.   Temperatures at 1,000′ will be in the low 30 F range.

The pattern of clear and sunny weather is over.   An unsettled pattern is on tap for the next several days, with precip, cloud cover and cooler temps on its way.

_________________________________________________________________________________________________________________

I will issue the next advisory tomorrow morning, April 7th.

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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.