Turnagain Pass RSS

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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sun, March 15th, 2020 - 7:00AM
Expires
Mon, March 16th, 2020 - 7:00AM
Forecaster
Ryan Van Luit
Avalanche risk The Bottom Line

Today the avalanche danger is LOW and could rise to MODERATE as the sun and increasing temperatures penetrate the snowpack.  As solar heating occurs, older slabs 1′-2′ thick and moist sluffs could become easier to initiate on steep slopes.  On steep slopes protected from the sun and wind, loose snow is expected to be easily triggered.  Cornices are large in some areas and weaken with the weather expected today, so give them a wide margin.

SUMMIT LAKE to LOST LAKE and SEWARD:  Extra caution is advised. Triggering a larger slab avalanche is possible in these regions due to several layers of weak snow existing deeper in the snowpack. This area was highly impacted by strong outflow winds last week.

Special Announcements

A wet avalanche narrowly ran past two people in the couloir near mile post 107 on the Seward Highway. This was a southerly aspect and was estimated at a vertical run of 1500′. Also, a very large avalanche was remotely triggered in Chugach State Park on Thursday. This was in the Eagle River (South Fork) area and no one was caught. Please take a look at that report HERE if headed this way.

Summer trails:  Wet loose avalanches in steep rocky terrain may begin to send debris near or over summer trails with the warm weather. Places such as the ice caves up the Byron Glacier trail sit directly in an avalanche path and are not recommended to travel to during the warm spring weather.

Sun, March 15th, 2020
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
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
  • Persistent Slabs
    Persistent Slabs
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
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.
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

The weather forecast for today calls for clear sunny skies, calm to light west winds, and temperatures peaking near the freezing level at 3000′.

As the sun and increasing temperatures affect the region today, surface conditions could become less stable and also impact our sporadic persistent slab concerns found within the top 1′-2′ of the snowpack.  An observer shared images illustrating the wet/moist loose avalanche concern from yesterday afternoon.  Steep slopes on easterly, southerly, and westerly solar aspects where slopes heat up enough are the most likely spots for a person to initiate these avalanches.  If triggered, this avalanche concern is expected to be on the smaller side of the scale, but could become entrained and move a rider or skier down the fall line.  Remain aware of your surroundings and anticipate your exit strategy as the terrain dictates.

The snowpack in more remote areas could be quite different. Pay attention to signs of recent avalanches, cracking/whumpfing, wind effect, and sun effect. Also, keep in mind areas with a shallow snowpack are more likely places to find a slab that fails in the weak layer described above or other old weak snow buried in the pack. This includes the south end of Turnagain Pass, such as Twin Peaks and Silvertip to Summit Lake and over toward Palmer Creek and the Raggedtop area near Girdwood.

A skier initiated wet loose avalanche on a southerly aspect of Magnum.  3.14.2020  Photo: Allen Dahl

Loose snow:  Loose dry snow still exists in many areas, especially on northerly aspects.  On steep slopes where this is the case, sluff could be easy for a human to initiate and could move down slope with enough volume to take a person off their feet.

Cornices:  We have some large cornice formation in many areas.  As the sun and increased temperatures beat down, it could become easier to trigger these.  As usual, it’s prudent to give cornices a wide berth and limit your time beneath them.

Weather
Sun, March 15th, 2020

Yesterday:  Sunny skies with light ridgetop winds from the west. Temperatures warmed to the mid 20’s°F along ridgetops and 30°F at the lower elevations.

Today:  More clear skies and sun! West winds are expected to be calm to light with temperatures just above freezing at sea level and 24°F-30°F at 3000′.

Tomorrow: More sun during the day with a high near 34°F at sea level. West winds are expected around 5 mph.  In the evening, winds are expected to shift becoming southwest as clouds increase to set up Tuesday for possible precipitation.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 22 0 0 67
Summit Lake (1400′) 19 0 0 30
Alyeska Mid (1700′) 23 0 0 77

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 25 WSW 7 14
Seattle Ridge (2400′) 25 VAR 1 5
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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.
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