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ARCHIVED - Forecasts expire after 24 hours.
Issued
Thu, November 23rd, 2023 - 7:00AM
Expires
Fri, November 24th, 2023 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger is MODERATE at all elevations. Due to the warm weather and rain, wet snow avalanches will be possible to trigger on slopes from sea level up to around 2,500′. Watch for soggy wet snow on steep terrain features. In the high elevations where dry snow exists, it will be possibly to trigger a slab avalanche 1-3′ deep. This could be a wind slab from yesterday’s winds, or a slab breaking on an older weak layer.

Roof Avalanches:  Snow has been sliding off roofs during this warm weather. Be cautious of people, kids and animals straying under snow laden roofs.

Special Announcements

Happy Thanksgiving Everyone!
We are incredibly thankful for your longstanding support that keeps our center operating and growing.

 

Chugach State Park:  Strong winds impacted the Anchorage Front Range yesterday. There was a report from Flattop of a skier triggered wind slab that caught the skier; they are OK. The new Weekend Avalanche Outlook for this area will start Dec. 1.

Hatcher Pass;  Check out HPAC’s Thursday’s avalanche report here:  hpavalache.org.

Thu, November 23rd, 2023
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
Fri, November 24th, 2023
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
3 - Considerable
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
Avalanche risk
Fri, November 24th, 2023
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
3 - Considerable
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.
Recent Avalanches

No new avalanches have been reported in our forecast area. The last known avalanche was skier triggered in Goldpan on Nov 18th. During the cold snap several glide avalanches released in the Girdwood Valley, Turnagain Pass, and Summit Lake area.

Avalanche Problem 1
  • Wet Loose
    Wet Loose
  • Aspect/Elevation
  • 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.

Aspect/Elevation of the Avalanche Problem
Specialists develop a graphic representation of the potential distribution of a particular avalanche problem across the topography. This aspect/elevation rose is used to indicate where the particular avalanche problem is thought to exist on all elevation aspects. Areas where the avalanche problem is thought to exist are colored grey, and it is less likely to be encountered in areas colored white.

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 cold and snowy start to November, the tide has turned. Yesterday a warm storm impacted our region with rain up to 2,000′ and east winds gusting in the 60’s mph. That storm moved out last night, but lingering showers will continue today along with the warm temperatures. We are expecting 1-3″ of wet snow above 2,000′ today and .1-.5 of rain below. Another pulse of rain, wet snow, and wind is slated for tonight and into tomorrow.

That all said, wet snow avalanches will be our main concern from sea level up to around 2,500′ in elevation. With no visibility yesterday it’s hard to say how the slopes reacted to the first punch of rain on snow. If anyone ventures out today, triggering an avalanche composed of wet soggy snow is definitely possible. Even small terrain features, in the Tincan Trees for example, can be dangerous if heavy wet snow pushes a person into a tree well or depression. Additionally, if we start a small wet snow avalanche on top of a larger steep slope, it could generate a significant amount of debris and run further than expected.

 

A snapshot of the Turnagain Pass weather forecast (1,000′ in elevation) from our ‘current weather page‘ provided by the National Weather Service. 

 

Turnagain Pass ‘North View’ midday yesterday. This is from the AK DOT&PF Road Weather Information System camera that sits near the top of the Pass. 11.22.23.

Avalanche Problem 2
  • Persistent Slabs
    Persistent Slabs
  • Aspect/Elevation
  • 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.

Aspect/Elevation of the Avalanche Problem
Specialists develop a graphic representation of the potential distribution of a particular avalanche problem across the topography. This aspect/elevation rose is used to indicate where the particular avalanche problem is thought to exist on all elevation aspects. Areas where the avalanche problem is thought to exist are colored grey, and it is less likely to be encountered in areas colored white.

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

At the higher elevations where the snow is drier, two types of dry snow avalanches could be possible to trigger. These are wind slabs and persistent slabs.

Wind Slabs – above 2,500′:  It’s a sure bet that wind slabs formed yesterday with winds in the 40-60mph range. These slabs should ‘heal’ quickly with the warm temperatures, but some could still be reactive today. Watch for the classic signs of wind deposited snow, stiffer snow over softer snow and cracks that may shoot out from you.

Persistent Slabs – above 3,000′:  At the even higher elevations we are still keeping in mind the chance a person could trigger a large avalanche up to 3 feet deep. There was a layer of weak snow at the base of the snowpack that caused a large avalanche 11 days ago in Goldpan bowl and a layer of buried surface hoar that created a foot deep but spooky avalanche 5 days ago in Goldpan. These layers should be becoming less likely to create avalanches as time goes on, but we still want to have them in our minds if we make it to the high elevations.

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

Glide avalanches have been occurring in the region during the cold snap, so far in areas that are not often traveled. Once the skies clear, it will be interesting to see if any glide avalanches released during the warm weather. As always, avoid being under glide cracks in case they spontaneously release.

Weather
Thu, November 23rd, 2023

Yesterday:  Warm, wet, and wind weather was over the region. Between 3-6″ of wet snow fell at the mid elevations with up to 2″ of rain at sea level in the Portage Valley. Rain snow line hovered around 1,500′. Ridgetop winds were 25-45mph with gusts in the 60’s from an easterly direction. Temperatures climbed to 40F at sea level at 36F at 1,500′ overnight where they are sitting this morning.

Today:  The main storm has moved out with decreasing precipitation and winds but temperatures are still warm. The rain snow line looks to remain close to 2,000′. Light showers are expected today (.1 – .5″ rain below 2,000′ and 1-4″ snow above) before another pulse of moisture is expected tonight (.3-1″ rain and 3-10″ wet snow above 2,000). Winds today should remain easterly 10-20mph with gusts in the 30’s, increasing again tonight (20-30mph gusts to 50).

Tomorrow:  Warm weather continues on Friday with light rain showers up to 2,000′ and snowfall above that. Ridgetop winds look to stay in the 10-20mph Friday from the east. More stormy weather is forecast for Sunday but this event looks a bit cooler and will hopefully bring the snow levels down.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 33 3 0.3 33
Summit Lake (1400′) 32 0 0 19
Alyeska Mid (1700′) 33 5 0.62 31
Bear Valley – Portage (132′) 39 rain 2.4

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 26 NE 30 68
Seattle Ridge (2400′) 28 SE 15 33
Observations
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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.