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Issued
Mon, December 26th, 2016 - 7:00AM
Expires
Tue, December 27th, 2016 - 7:00AM
Forecaster
Aleph Johnston-Bloom
Avalanche risk The Bottom Line

A  BACKCOUNTRY AVALANCHE WARNING was issued through the National Weather Service yesterday  and remains in effect until 6 pm today  for the Turnagain Pass area and surrounding mountains.  

Heavy snowfall and strong winds have created a  HIGH avalanche danger  in the mountains surrounding Turnagain Pass, Girdwood Valley, Portage Valley and areas on the Kenai seeing heavy snowfall.  Dangerous avalanche conditions are expected on all slopes  30 degrees and steeper – including runout zones. Large avalanches are expected to release naturally, be easily triggered by people and could run to elevations below 1,000′.  

Travel in avalanche terrain is NOT recommended.  

Special Announcements

Turnagain Pass is now OPEN to motorized use . This opening happens to coincide with HIGH AVALANCHE DANGER! It is recommended to AVOID AVALANCHE TERRAIN until this storm settles. There is plenty of fun riding to be had in the flats, away from avalanche terrain and runout zones.  

DOT plow drivers are doing their best to keep up with this storm. Keeping the Seward Highway clear is their priority over recreational parking.  Please be respectful and avoid parking on the highway! As of last night (11PM) PARKING LOTS HAVE NOT BEEN PLOWED YET AT TURNAGAIN PASS. Berms were too large to drive a truck in.  

Check out the Summit Lake Summary  HERE.  

Mon, December 26th, 2016
Alpine
Above 2,500'
4 - High
Avalanche risk
Treeline
1,000'-2,500'
4 - High
Avalanche risk
Below Treeline
Below 1,000'
3 - Considerable
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
  • Storm Slabs
    Storm Slabs
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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 natural avalanches 2 ft. deep were observed. These were long running and large enough to bury and kill a person. Cracking and collapsing (whumpfing) were also observed.

Red flags… Rapid loading = Expect dangerous avalanches.

STORM TOTALS in the upper elevations so far:

Turnagain Pass:     30+” and counting, 2.8″ of H2O
Girdwood Valley:    20+” and counting,  1.6″ of H2O
Summit Lake:         4-6″, .4″ of H2O

Snow continues to fall with another 1-4″ inches expected today.  16″- 20″ of snow was measured yesterday on Turngagain Pass. An additional 10+ inches has fallen since then. All of this new snow is forming thick slabs, especially in the alpine where consistent easterly winds have been blowing into the 40’s. The weak surface snow and weak snowpack have been rapidly loaded. Expect natural avalanches today and that triggering an avalanche is very likely on any slopes over 30 degrees. Avalanches have the potential to be long running and could be remotely triggered. Avoid travel underneath avalanche terrain as well. This includes the Seattle Ridge up-track and all slopes, gullies and runout zones. 

This needs to be highlighted again today:

Treed areas such as the Tincan Trees:  Storm snow slab avalanches 2-3′ thick are likely to be triggered in the trees. The new snow is denser than the underlying old snow – creating an upside down and unstable snowpack. Avoiding slopes over 30 degrees in treed areas is also recommended. Due to the weak faceted snow below the new snow the snowpack is “bottomless”. Movement through the snow was challenging yesterday and will only be more of a struggle today. 

Travel in avalanche terrain is NOT recommended. Deep, dangerous avalanches are likely. BE PATIENT. 

Natural avalanche in the Snake Pit on Tincan, 12.25.16. The next gully over also slid. 

Weather
Mon, December 26th, 2016

Yesterday skies were obscured and it snowed or rained depending on elevation throughout the day with periods of heavy precipitation. Easterly winds were in 20s gusting into the 40s. Temperatures were in the 20Fs at ridge tops and in 30s in the valleys. Rain/snowline fluctuated around 500′. The storm continued overnight and temperatures are rising slightly this am.  

Today will be cloudy and another 1-4″ of snow is forecasted to fall, rain below 400′. Temperatures are forecasted to hover around freezing, either above or below depending on elevation. Winds will remain easterly 5-15 mph with higher gusts in the alpine. The snow showers are forecasted to continue overnight into tomorrow with temperatures cooling and winds becoming calm.  

Tomorrow is forecasted to be cloudy with a slight chance of snow showers, temperatures in the low 20Fs and light NW winds.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 29    20  2  50 + (estimate)
Summit Lake (1400′)  31  2 .2    10
Alyeska Mid (1700′) 31    10  .9  32

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) Under repair      Under repair   Under repair      Under repair  
Seattle Ridge (2400′) 24   rimed   rimed   rimed  
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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.