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ARCHIVED - Forecasts expire after 24 hours.
Issued
Tue, November 27th, 2018 - 7:00AM
Expires
Wed, November 28th, 2018 - 7:00AM
Forecaster
Aleph Johnston-Bloom
Avalanche risk The Bottom Line

As wet and stormy weather continues today the avalanche danger remains HIGH in the Alpine. With additional snowfall and wind loading natural avalanches are likely.  Avalanches at upper elevations may run into terrain below keeping the danger at CONSIDERABLE for the Treeline elevation band. Human triggered avalanches are very likely above the rain/snow line (approximately 2500′). Travel above treeline is not recommended.  

Special Announcements

The Friends of the CNFAIC have two scholarships dedicated to avalanche education. The funds generated to make these possible are in celebration of Rob Hamel and Amy Downing, their love and passion for the mountains, and to help others stay safe. We encourage you to read each one and apply if you fit the need, or pass along to someone who could benefit. Applications due on Dec 1st.

Rob Hamel Scholarship Fund   €“ For recreational users and professional avalanche workers.

Amy Downing Scholarship Fund   €“ For recreational users.

Both of these scholarships are supported by your generous donations. Today is #GivingTuesday. Consider a donation to the Friends of the CNFAIC. Donate HERE. Thank you for your support.  

Tue, November 27th, 2018
Alpine
Above 2,500'
4 - High
Avalanche risk
Treeline
1,000'-2,500'
3 - Considerable
Avalanche risk
Below Treeline
Below 1,000'
0 - No Rating
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
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
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.

Likelihood of Avalanches
Terms such as "unlikely", "likely", and "certain" are used to define the scale, with the chance of triggering or observing avalanches increasing as we move up the scale. For our purposes, "Unlikely" means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. "Certain" means that humans will be able to trigger avalanches on many slopes, and natural avalanches are expected.

Size of Avalanches
Avalanche size is defined by the largest potential avalanche, or expected range of sizes related to the problem in question. Assigned size is a qualitative estimate based on the destructive classification system and requires specialists to estimate the harm avalanches may cause to hypothetical objects located in the avalanche track (AAA 2016, CAA 2014). Under this schema, "Small" avalanches are not large enough to bury humans and are relatively harmless unless they carry people over cliffs or through trees or rocks. Moving up the scale, avalanches become "Large" enough to bury, injure, or kill people. "Very Large" avalanches may bury or destroy vehicles or houses, and "Historic" avalanches are massive events capable of altering the landscape.

Signal Word Size (D scale) Simple Descriptor
Small 1 Unlikely to bury a person
Large 2 Can bury a person
Very Large 3 Can destroy a house
Historic 4 & 5 Can destroy part or all of a village
More info at Avalanche.org

With the active weather the avalanche danger remains elevated. Snow at upper elevations and rain at lower elevations is expected to continue today. Rain/snow line is forecast to be around 2500′. Winds are forecast to be easterly with gusts into the 40s.  Our road observations yesterday had limited visibility but a few wet loose avalanches were observed to have run in the mid-elevation band. Rain continues to wash away the snow that fell on Saturday night in this elevation band. 

Water totals at the mid-elevation snow stations for this soggy storm cycle:

  • Girdwood Valley at 1,700′:  4″ of water equivalent 
  • Turnagain Pass at 1,880′:  3″ of water equivalent
  • Summit Lake at 1,400′: 0.9″ of water equivalent 

If we convert the water to snow at upper elevations we have a significant load. We are uncertain at this point about avalanche activity in the Alpine. However snow continues to fall, the winds are sustained and we know this is loading older layers of snow. With this recipe we have to expect storm slab avalanches. 

Rookie Hill with a few small wet loose avalanches in the channeled terrain on Seattle Ridge. November 26, 2018, Photo: Wendy Wagner

Tincan: Snow that fell Saturday night in the mid-elevation band getting rained on. November 26, 2018. Photo: Wendy Wagner 

Weather
Tue, November 27th, 2018

Yesterday:  Rain and snow throughout the day. Rain/snowline was around 2500′. Temperatures were in the high to mid 30Fs at lower elevations and low 30Fs to high 20Fs at upper elevations. Winds were easterly 15-25 mph with gusts into the 40s.  

Today:  As a low in the Gulf continues to push moisture and warm air into the region rain and snow showers will continue. Half to three quarters of an inch of water is forecast to fall. Rain/snowline will remain around 2500′ before lowering Wednesday as cooler air moves in. Winds will be from the E-SE 20-30 mph with gusts into the 40s. Temperatures will be in the 40Fs to high 20Fs depending on elevation.  

Tomorrow:  A trough bringing cooler air is forecast to push up Cook Inlet with the potential to bring snow to Anchorage and Hatcher Pass. The advisory area should see a shift to snow showers with cooling temperatures later in the day into Thursday. The timing on all this is fairly uncertain as the weather models are not in agreement.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 36   0    0.8  13
Summit Lake (1400′) 35   0  

 0.4

 0
Alyeska Mid (1700′) 36   0    1.59  0

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′)  29  NE 16    50
Seattle Ridge (2400′)  32  E 11  40
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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.