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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sat, December 5th, 2015 - 7:00AM
Expires
Sun, December 6th, 2015 - 7:00AM
Forecaster
Graham Predeger
Avalanche risk The Bottom Line

Weak snow exists in upper elevations of the advisory area where the avalanche danger is  MODERATE  above 2500′.   As you move up in elevation a persistent weak layer can be found at the base of our snowpack and human triggered avalanches are possible.

All areas below ~2,500′ are exhibiting  LOW  avalanche danger as temperatures have stayed below freezing and snowfall has been modest and incremental over the last week.

**If northerly winds kick up today earlier than expected, we’ll see shallow, sensitive wind slabs on slopes with a southerly tilt.**

Special Announcements

The 7th annual Alyeska Ski Patrol Auction (benefiting the avalanche canine program) is happening tonight at the Sitzmark in Girdwood.   Always a good party, this is not to be missed!

See latest Alaska Dispatch News article HERE for more information on missing skier Liam Walsh in Hatcher Pass.

Sat, December 5th, 2015
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
  • 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

Observations yesterday point toward weak snow at the ground in the upper elevations (above 3,000’) that show significant potential to propagate.  We are unclear how widespread these basal facets are across the forecast zone and with no other red flags (recent avalanches, whumphing or shooting cracks) reported in nearly a week, our snowpack is sending us a bit of a mixed message this weekend.  It’s the kind of avalanche problem (persistent slab) that may not present itself until a skier finds the sweet spot and triggers an avalanche, potentially after several tracks on the slope. So, if the plan is to push into bigger, steeper, above treeline terrain today, it’ll be worth digging a quick pit to see if you can find loose, faceted snow at the very bottom of the snowpack.  Look for snow with the consistency of a handful of sugar and if found, recognize that as your weak interface.

                                    

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

The snow quality right now is arguably the best it’s been in over a year so no doubt the usual zones in Turnagain will be crowded.  Keep other adjacent groups in mind as you are moving through the mountains today and maintain good backcountry etiquette.  Wear and know how to use your rescue gear, expose one person at a time on a slope, discuss potential consequences if a slope does slide and don’t ski on top of other parties.

8-10″ of new snow made for great skiing at 3,000′ on Sunburst ridge yesterday.  Keep in mind that If northerly winds kick up today earlier than expected, we’ll see shallow, sensitive wind slabs on slopes with a southerly tilt given the substantial amount of loose snow available for transport.

Weather
Sat, December 5th, 2015

Yesterday was again marked by mild weather throughout the forecast zone.   Temperatures were comfortable in the 20’s, winds very light out of the East and just a few intermittent snow showers throughout the day not really amounting to much accumulation.

Today we can expect more of the same with morning fog eroding to clearing skies throughout the day and no new precipitation.   The winds are expected to increase throughout the day and into this evening from the North but are not expected to be much above 20mph at ridgetops.  Temperatures will be in the low 20’s F at ridgetops and the high 20’s to low 30’s F at 1,000′.   Prepare for a couple more days of high pressure before our next shot of unsettled weather has the potential to move into the region next Tuesday/ Wednesday.

PRECIPITATION 24-hour data (6am – 6am)

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 24   0   .1   23  
Summit Lake (1400′) 20    0  .1  12
Alyeska Mid (1700′)  26  0  0  19

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′)  18  NE  5 15  
Seattle Ridge (2400′)  21  N/A  N/A N/A  
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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.