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Archives
ARCHIVED - Forecasts expire after 24 hours.
Issued
Sat, March 23rd, 2013 - 7:00AM
Expires
Sun, March 24th, 2013 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

There is a MODERATE avalanche danger today above treeline for wind slab avalanches. These will be soft, shallow and possible to find and trigger in areas that received 6 inches or more of new snow yesterday. Slopes most suspect are steeper than 35 degrees on west and southerly aspects where fresh wind deposited snow exists over the top of a crust. Areas that picked up less than 6 inches of snow, including below treeline, the danger is LOW where triggering an avalanche remains unlikely.

Special Announcements

One week from tomorrow is the 2nd ANNUAL CORN HARVEST – get it on your calendar now !! Come join the CNFAIC Friends and Forecasting staff on Turnagain Pass for free food, games, prizes, etc. This is one way we would like to thank all of you for your dedication and support. Oh, did I mention, it’s FREE?

Sat, March 23rd, 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

Yesterday was our first chance in just over a week for a dose of fresh snow to cover the plethora of old tracks. We did get enough to do so in some locations but not quite enough in others. Most stations are reporting around 5-6” of low desnity snow (thanks to our cold temperatures) in the past 24 hours. A bit more can be expected at the higher elevations as well as in favored areas such as the northern side of Turnagain Pass and the Girdwood Valley.

Winds associated with yesterday’s snow were moderate from the east and having an easy time blowing the light snow into shallow drifts and soft slabs. This wind deposited snow has covered up all types of old surfaces such as sun crusts, wind crusts, old wind slabs and near surface facets (old soft powder). All of these surfaces will inhibit good initial bonding of the new snow. Wind slabs today should be soft and in the 4-12” range depending on how much snow fell in the area you are traveling. Watching for wind drifted snow and new snow that cracks out from your sled, board or skis will be the key. Expect any slide triggered on a crust or hard surface to run fast and far.

Additionally, watch for soft slabs in wind sheltered areas. The warming temperatures overnight will cause the loose snow from yesterday to bond forming an upside down layering. This warming will eventually help the new snow to stick to the underlying surfaces but, there is a window where the new snow becomes more reactive first. Keep this in mind in areas with greater amonts of snowfall.

Below is an image of cracking in a small fresh wind slab from yesterday – something to watch for today.

If you are traveling in the Summit Lake area old wind slabs are a concern. Check out the Summit Advisory as well as Fitz and Kevin’s observation from yesterday.

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

Any new snow will easily slide on the old surfaces – especially where a crust sits underneath. Triggering a sluff is most concerning where new snow amounts are ~6” or greater.

Additional Concerns:
Don’t forget about steering clear of looming cornices. The temperature has gone up significantly in the past 24 hours at the upper ridgetops and this will increase the likelihood of cornice failures.

Surface Conditions:
Needless to say, the surface conditions are a bit variable with scoured areas alongside soft wind drifts. The best riding is likely in wind sheltered locations where a few inches of new snow on a crust or soft old snow can be found.

Weather
Sat, March 23rd, 2013

After 7 days of clear skies, yesterday a weak low pressure moved in from the west and we were back to snow and low visibility. During the past 24 hours we have picked modest amounts of low density snow:

–                   Turnagain Pass €“    ~5 € (.4 water equivalent)
–                   Alyeska €“  ~5 € (0.34 water equivalent)
–                   Summit Lake €“ ~3 € (0.3 water equivalent)
–                   Hatcher Pass is reporting around a foot, maybe more. Check out the Hatcher Pass Avalanche Center if you are thinking of heading that way.

Winds have been out of the east predominantly in the 25mph range with gusts to 40 but have decreased overnight and shifted to a more southerly direction. Temperatures have been warming steadily from this time yesterday – Ridetops from ~10F to ~20F and 2,000′ from the mid-teens to mid 20’s.

Today we can expect cloudy skies with intermittent snow showers as yesterday’s system moves out. Accumulations today should be a trace to an inch. Winds will be out of the southeast at 5-10 mph with gusts to 15. Temperatures look to remain mild, in the mid to upper 20’s F at 1,000′ and 20F near on the Ridgetops.

Another low is heading to our south by Sunday bringing another chance for precipitation Sunday into Monday.

The Sunburst weather station should be up and running by Monday or Tuesday. There are some modifications with the webcam being done and it seems a fuse has been blown in the midst.

 


Fitz will issue the next advisory tomorrow morning, March 24th.

Observations
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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.