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ARCHIVED - Forecasts expire after 24 hours.
Issued
Mon, February 19th, 2024 - 7:00AM
Expires
Tue, February 20th, 2024 - 7:00AM
Forecaster
Andrew Schauer
Avalanche risk The Bottom Line

The danger remains CONSIDERABLE above 2500′. A storm is expected to arrive this afternoon, with increasing east winds making wind slab avalanches likely through the day. This storm will start adding stress to a deeper weak layer of snow that may produce bigger avalanches. Pay attention to changing conditions, and be prepared to adjust your travel plans if the storm arrives sooner than expected. The danger is MODERATE below 2500′, but will rise to CONSIDERABLE overnight as the snow starts to accumulate and natural and human-triggered avalanches failing within new and windblown snow become more likely.

SNUG HARBOR/LOST LAKE/SEWARD: The Seward area is expected to see the most intense precipitation with the approaching storm, with close to a foot of snow possible during the day today, and more on the way tonight. Expect to see very dangerous avalanche conditions as the storm picks up through the day, and be prepared to get out of avalanche terrain as the snow starts to accumulate.

Special Announcements

Chugach State Park: The National Weather Service has issued a Special Weather Statement for strong winds expected to impact the Front Range during stormy weather the beginning of this week.

Forecaster chat Friday, February 23 from 5-6 pm at the Seward Community Library and Museum community room. For our friends down on in Seward and Moose Pass, come chat with us about the product we are producing called the “Weekend Avalanche Outlook”. We’ll also be talking about the state of the snowpack in Summit and Seward, and any other questions you have. More info Here.

Mon, February 19th, 2024
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
Avalanche risk
Tue, February 20th, 2024
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
3 - Considerable
Avalanche risk
Below Treeline
Below 1,000'
3 - Considerable
Avalanche risk
Tue, February 20th, 2024
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
3 - Considerable
Avalanche risk
Below Treeline
Below 1,000'
3 - Considerable
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

It has been 5 days since the last known human-triggered avalanche, which was a large wind slab in the Placer Valley. We have seen natural wet loose and wind slab avalanches during the past week of warm and windy weather, but no new activity was reported yesterday.

Avalanche Problem 1
  • Wind Slabs
    Wind Slabs
  • Aspect/Elevation
  • 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.

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

It is looking like a much-needed refresh is on the way, and stormy weather is expected to pick up today through tomorrow. For today, most of our advisory area is only expected to receive a trace to 3″ new snow which is not really enough to increase the avalanche danger on its own. However, with strong easterly winds picking up through the day, it is likely a person will be able to trigger a wind slab avalanche in the upper elevations and we may see some small wind slabs forming near our treeline elevation band. The most likely places to encounter sensitive wind slabs will be just below ridgelines, on convex rollovers, and in steep gullies. Watch out for red flags like shooting cracks, collapsing, or fresh avalanches as clear signs of dangerous conditions. Safe travel today will require careful snowpack assessment, avoiding slopes that have been recently loaded. Avalanche danger is expected to increase as the storm unfolds, so be prepared to adjust your travel plans if the storm arrives early. Keep in mind, this round of snow and wind is adding weight on top of a deeper weak layer which may make bigger avalanches.

 

Predicted snow totals for the next 24 hours. Graphic courtesy of NWS Anchorage. 02.19.2024

An older wind slab in the Lynx Creek drainage, likely from last week’s strong winds. The chances for similar activity will increase today as the wind picks up again. Photo: Thomas Lees/AAS Moto Rec. 2. 02.18.2024

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

We are still concerned about the weak layer of facets that formed during the January dry spell and is now buried 1-2 feet deep. As mentioned above, the approaching storm is expected to add stress to this weak layer, increasing the likelihood of a bigger avalanche. These deeper weak layers can be difficult to assess, and our normal travel tests like hand pits and test slopes do not give reliable feedback. You’ll have to take the time to dig a pit and test the weak layer of concern if you want to gain a little more information on how reactive it is in the are you are traveling. This week’s warm weather is helping the layer to heal, and we’ve been seeing encouraging signs in the Turnagain Pass area. However, it may be more concerning in the Crow Creek, Placer, and Summit areas. You can avoid the problem entirely by simply sticking to lower angle terrain until the layer has a little more time to heal.

A week of warm weather is helping the weak layer to heal. Those test codes on top of the January facet layer are encouraging test results, suggesting the weak layer is gaining strength. That said, it is still down there and still worth paying attention to. Photo: Andy Moderow, 02.18.2024

Weather
Mon, February 19th, 2024

Yesterday: Weather was fairly quiet yesterday, with overcast skies, warm temperatures, and light easterly winds around 5 to 15 mph. We received 0.1” precipitation in the past 24 hours, with light rain up to around 2000 to 2300’. High temperatures were in the upper 20s to upper 30s F, with lows in the mid 20s to mid 30s F.

Today: A storm is expected to begin to impact our area today, starting with increased easterly winds around 20 to 30 mph with gusts of 30 to 45 mph. Most areas will see a trace to 3” snow during the day, with the exception of the Seward zone, which could see closer to 4” to 10” by sunset. The rain line is expected to start to drop today from 2000’ down to 1500’, with high temperatures in the mid to upper 30s F and lows in the low to mid 30s F.

Tomorrow: Tomorrow should be the peak of the approaching storm, with 8-12” snow expected in Turnagain Pass, 12-18” expected in Girdwood and Summit Lake, and 2-3 feet in the Seward zone. East winds are expected to ramp up to 25-45 mph with gusts of 30-60 mph. The rain level should keep dropping, making it down to around 300-500 feet as the storm continues into Tuesday night.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 33 0 0.1 83
Summit Lake (1400′) 34 0 0 41
Alyeska Mid (1700′) 35 tr 0.08 90
Bear Valley – Portage (132′) 37 0 0.32
Grouse Ck (700′) 37 0 0 60

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 26 ENE 10 26
Seattle Ridge (2400′) 29 SE 10 20
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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.