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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sun, April 14th, 2019 - 7:00AM
Expires
Mon, April 15th, 2019 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger is MODERATE on slopes above 2,500′. Wet loose sluffs could be easy to initiate on steep sunny slopes by this afternoon/evening. Sluffs could become larger than expected if surface warming melts the top 4-6″ of the snowpack. On high elevation north aspects (above 3,000′), triggering a dry slab avalanche may be possible due to a weak layer buried 1-2′ deep. As always, give cornices a wide berth and limit travel under glide cracks.

PORTAGE VALLEY: Cornice fall and/or avalanches from above have the potential to send debris to valley bottoms and into snow-free zones. Traveling along hiking trails, such as the Byron Glacier Trail with steep slopes overhead, is not recommended this afternoon/evening during the heat of the day.

LOST LAKE / SEWARD:  Similar to Turnagain, wet loose avalanches on sunny slopes are possible with the heat of the day. Dry slab avalanches could be a concern on high elevation northerly slopes.

MONDAY AVALANCHE OUTLOOK: No avalanche forecast will be issued tomorrow. Similar avalanche conditions are expected on Monday, Apr 15th. Watch for increased surface heating by the sun and wet loose avalanches on slopes with wet, mushy snow.

Special Announcements

Daily advisories end today  (Sunday, Apr 14th). For the remainder of April, advisories will be posted 4 days/week (on Tues, Thur, Sat and Sun). The avalanche center will close for the season on Saturday, April 27th when we will post our springtime tips. Thank you everyone for tuning in!

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Sun, April 14th, 2019
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
1 - Low
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. 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
  • Wet Loose
    Wet Loose
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
Wet Loose
Wet Loose avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
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

A couple sunny days are in the forecast and we are generally back into a springtime avalanche regime. Meaning, low hazard in the morning (frozen snow surface) transitioning to a moderate hazard in the afternoon on solar aspects (melting snow surface). Wet loose sluffs should be easy to trigger once sunny slopes warm enough to melt the top 2-3″ of frozen snow. If the surface becomes even more sloppy (6″ or more of wet/mushy snow) then sluffs could become larger and more dangerous, especially in larger terrain. Paying attention to surface warming/melting will be key for the next several days.

Other springtime concerns are cornice falls. Cornices heat up and can destabilize rapidly during daytime warming; making them easier to trigger.

 

Cornice along the Sunburst ridge yesterday.

Avalanche Problem 2
  • 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

In the dry snow that sits on shaded aspects generally above 3,000′, even over 3,500′ in places, a questionable weak layer exists 1-2′ below the surface. The layer is composed of facets and buried surface hoar and was found at 3,300′ on Tincan. It is suspect to be lurking on other high elevation northerly slopes. We had a good look around yesterday and did not see signs of natural avalanches breaking in the layer during last Thursday’s storm, which is good news, but we still need to tread cautiously. Listening for whumpfing and digging a test pit to look for and test the layer are good ways to gather information. Sticking to safe travel protocol is also wise; exposing one person a time, watching our partners and having escape routes planned.

Taylor Pass and Basketball Chute on the right. Many higher elevation northerly aspects remain intact. The only evidence of avalanche activity from Thursday’s storm were old wind slabs; no signs of avalanches breaking in deeper weak layers.

Additional Concern
  • Glide Avalanches
    Glide Avalanches
Glide Avalanches
Glide Avalanches are the release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. They are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.
More info at Avalanche.org

A few glide cracks that were filled with new snow on Thursday are slowly opening up again. This tells us some movement is still taking place. A chance remains that a crack could release into an avalanche. It has been a week since the last known glide released (Hope Wye area south of Turnagain). Being suspect of cracks and limiting/avoiding time spend under them is always a good idea as they can avalanche at any time.

Seattle Ridge with the up-track on the looker’s right of photo. After many glide avalanches turned this ridge brown, new snow has brightened it up a bit. It has been over a week now since any glide avalanches have occurred on this slope – that doesn’t mean one can’t occur today however. 

Weather
Sun, April 14th, 2019

Yesterday:   Partly cloudy skies were over the region as high pressure slowly built in. Ridgetop winds have been light over the past 24-hours, blowing 5-10mph from the east. Temperatures climbed to 30F at 4,000′ and to 40F at 2,000′. Clear skies have allowed overnight temperatures to cool to the upper 20’sF below 2,500′.

Today:   Mostly sunny skies with light and variable winds are expected. Temperatures should climb to 32F, or higher, at 4,000′ and to the mid 40’sF at 2,000′.

Tomorrow:   Monday we can expect another sunny day that could be slightly warmer than Sunday. Winds should remain light with an easterly push (~5mph). One more clear sky day for Tuesday before clouds and a chance for precipitation heads our way Wed/Thurs.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 34 0 0 64
Summit Lake (1400′) 32 0 0 18
Alyeska Mid (1700′) 34 0 0 58

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 26 NE 6 21
Seattle Ridge (2400′) 31 SE 4 10
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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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