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Issued
Wed, March 31st, 2021 - 7:00AM
Expires
Thu, April 1st, 2021 - 7:00AM
Forecaster
Aleph Johnston-Bloom
Avalanche risk The Bottom Line

The avalanche danger is MODERATE at all elevations. Triggering a slab avalanche 1-3′ deep is possible on slopes 35° and steeper on buried layers of weak snow. With NW winds in the forecast today, watch for wind transport and fresh wind slabs developing at upper elevations. Assess the snowpack as you travel, identify areas of concern and evaluate terrain consequences. Avoid travel under glide cracks.

SUMMIT LAKE/SNUG/LOST LAKE/SEWARD:  Stronger NW winds are forecast for these zones and natural wind slab avalanches are possible. Additionally, slabs may step down into buried weak layers and create a larger avalanche.

Special Announcements
  • As of this morning the road to Hatcher Pass is still closed at Mile 14 due to avalanche danger. Please follow Hatcher Pass Avalanche Center’s social media updates and Alaska 511.
  • There was a partial burial on Harp Mountain in the South Fork of Eagle river on Monday.
Wed, March 31st, 2021
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. 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
  • 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

After a little new snow and a couple days of temperatures climbing above freezing, we are seeing a cooling trend this morning. The snow that became moist or wet yesterday should have a delightful crust today…  Cooler temperatures, cloudy skies and WNW winds should keep the crust locked up and prevent any wet loose avalanches or warming issues in the snowpack. Our main avalanche concern continues to be persistent slabs due to layers of weak snow buried in the top 1-3′ of the snowpack. The natural avalanches in Summit Lake on Monday likely failed on these buried weak layers, as well as the most recent human triggered avalanches last week. These layers are still easy to find in snow pits and observers report variable results with snowpack tests. Some test results are pointing towards the potential for avalanches to be initiated on these layers. We have not been seeing widespread avalanches but we know these weak layers exist in the snowpack across the forecast area and south from Summit Lake to Seward. With wind loading today, triggering a wind slab avalanche (see Problem 2) could add stress to the layers below and result in a larger avalanche. Previously wind loaded slopes also harbor deeper slabs over the weak layers. Be on the lookout for areas that were previously wind loaded and those with any new wind loading. As always, use good travel protocol, and think about terrain consequences. This type of avalanche issue might allow you to get well out on the slope before the avalanche releases and it might not be the first person that triggers the avalanche.

Despite the weather forecast, because it is springtime and due the reality that we have dynamic weather, pay attention to cloud cover, temperature, and surface conditions. If the sun pokes out and/or temperatures shoot above freezing and you see signs of surface snow warming, move to shadier aspects/drier snow.

It was easy to see the line of buried surface hoar in a snow pit on Eddies yesterday, 3.30.21, at 2000′ on a N aspect. This weak layer was propagating in Extended Column Tests.

 

Avalanche Problem 2
  • Wind Slabs
    Wind Slabs
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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 moderate WNW winds in the forecast today and soft snow available for transport, watch for new small wind slabs to develop in the 6-8″ range. These are most likely to be found in the higher terrain along ridgelines. Watch for active wind loading and avoid any slope or cross-loaded gully with fresh wind deposited snow. Shooting cracks are a good indicator as well areas with stiffer snow over softer snow. As mentioned above, wind loading could overload buried weak layers and make it easier to trigger a larger avalanche. As we have said before, this wind flow direction is tricky for Turnagain Pass. It can funnel through the Pass from the south and load north aspects on the non-motorized side, while at the same time load the SE face of Seattle Ridge. It can also split around the Pass and not affect much of the terrain in the heart of Turnagain at all. This wind direction often has a greater impact near Crow Pass, through Portage, and south of the forecast area from Summit Lake to Seward.

Loose snow avalanches: Steep slopes are that sheltered from the wind have loose snow sitting on top of firm surfaces. It will be easy to trigger dry loose avalanches (sluffs) in that terrain today, and they can pick up enough volume and speed to carry a person. While it is unlikely they will be big enough to bury you, they can be dangerous if they drag you into terrain traps like cliffs, trees, rocks, or gullies.

 

Weather
Wed, March 31st, 2021

Yesterday: Partly cloudy skies with brief snow showers around noon. Light winds and temperatures in the high 20°Fs to mid 30°Fs. Increasing clouds overnight with light winds and temperatures in the teens to mid 20°Fs.

Today: Mostly cloudy skies with a chance of snow. Winds will be WNW 5-15 mph with gusts into the 20s. Temperatures will be in the teens to high 20°Fs. Overnight skies remain cloudy with a chance of snow. Winds will continue from the WNW 5-15 mph with gusts into the 20s and temperatures will be in the teens and single digits.

Tomorrow: Cloudy skies to start the day, gradually becoming mostly sunny. Northwest winds 15-20 mph with gusts into the 30s and temperatures in the 20°Fs.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 27 0 0 112
Summit Lake (1400′) 29 0 0 50
Alyeska Mid (1700′) 28 0 0 118

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 19 W 5 25
Seattle Ridge (2400′) 25 E-W* 4 11

*Wind shift at 5 pm yesterday.

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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.