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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sun, March 22nd, 2020 - 7:00AM
Expires
Mon, March 23rd, 2020 - 7:00AM
Forecaster
Ryan Van Luit
Avalanche risk The Bottom Line

Today the avalanche danger is MODERATE.  2-6 inches of snow yesterday and 15-30mph northwest winds today are likely to create new wind slabs on leeward terrain.  Small sluffs in the new snow are expected in steeper terrain. Wet loose avalanches will be possible to trigger in lower elevations where winds are calm.

SUMMIT LAKE:  Increased wind and active loading could tip the balance today in this area. A shallower snowpack exists from the Johnson Pass and Silvertip trailheads south to Summit Lake. In this area, there remains a chance a person could still trigger a larger slab avalanche due to weak snow in the mid and base of the pack. Extra caution is advised.

PORTAGE VALLEY/Byron Glacier Trail: Strong wind will increase the avalanche danger in this zone. Avoid avalanche runout zones such as the Byron Glacier hiking trail up to the ice caves.

*Roof Avalanches:  Roofs may still shed remaining snow!

Special Announcements
  • Heading to Hatcher Pass? Please check the Hatcher Pass Avalanche Center’s Sunday Forecast HERE.
  • Check out a recent Chugach State Park avalanche observation HERE.
  • The CNFAIC is grateful for all those who have been submitting observations! Let us know what you see if you’re getting out in the mountains. You can submit on our website HERE or shoot us an email at staff@chugachavalanche.org. Thank you!!
Sun, March 22nd, 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
  • 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

Winds have picked up to 15-30mph from the northwest and are expected to continue through today as clouds part way to sunny skies this morning.  Temperatures are expected to range from the mid 30’s °F at sea level to the teens °F at upper elevations.

The northwest winds that built overnight are expected to continue throughout the day and are strong enough to move the  2-6″ of snow that fell throughout the region yesterday.  So, wind slabs are likely to continue forming on leeward aspects today, which could add to small wind slabs that formed yesterday.  Although they’re expected to be relatively small, 12-18″ thick, they could be easier to human trigger if they’ve formed on aspects with a sun crust or firm wind pressed snow.  If you see shooting cracks or feel a significant hardness difference at the new/old snow interface, it could be worth reconsidering your route.  Triggering this size of wind slab could take a person off their feet, so remain mindful while traveling in steeper terrain above cliffs and rocky outcrops, and in channelled terrain.

Breaking trail in 2-6″ of new snow yesterday under obscured skies.  3.21.20. Photo: A. Moderow

 

Winds have picked up over the past two days!

 

Dry Loose Snow avalanches:  Sluffs in the drier new snow at the higher elevations will be likely. These should be on the small side and composed of up to 6″ of yesterdays storm snow.

Cornices:  Cornices should grow a bit today with the sticky new snow and strong winds. As always, give them a wide berth and limit exposure underneath them.

Avalanche Problem 2
  • 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

Cloud cover and warmer temperatures yesterday have warmed the snow at lower elevations. As the clouds clear out this morning, it’s expected that the surface snow refroze in many locations, especially where the wind is blowing.  However, where conditions are just right – the temperature is near freezing, winds are calm and the sun is beating down, triggering a wet loose avalanche on saturated slopes will be possible. Keep this in mind in small creek beds and terrain traps in the trees.

Additional Concern
  • Persistent Slabs
    Persistent Slabs
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.
More info at Avalanche.org

Triggering a large slab avalanche that breaks in weak old faceted snow deeper in the snowpack remains a concern in areas that have a shallow overall snow depth. These areas are south of Turnagain Pass and include Johnson Pass to Silvertip area, Summit Lake and Palmer Creek. Watch for areas that have a harder wind packed layer of snow over weak sugary snow.

Weather
Sun, March 22nd, 2020

Yesterday:  2-6″ of snow fell throughout the day throughout the region. Ridgetop winds were easterly in the 15-25mph range. Temperatures were in the mid 20’s°F at the higher elevations and the mid 30’s°F at sea level.

Today:  Clearing skies are expected with a high near 35°F and lows in the teens °F.  Ridgetop winds are expected from the northwest ranging from 15-30 mph.  No precipitation is expected.

Tomorrow:  Mostly sunny skies are forecast with a high near 37°F and lows in the teens °F.  Moderate northwest winds are expected through the day trending to light by the evening.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 30 4 0.2 69
Summit Lake (1400′) 31 2 0.1 32
Alyeska Mid (1700′) 30 4.9 0.46 79.5

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 18 WNW 13 33
Seattle Ridge (2400′) 24 NW 13 29
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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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