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ARCHIVED - Forecasts expire after 24 hours.
Issued
Wed, February 28th, 2024 - 7:00AM
Expires
Thu, February 29th, 2024 - 7:00AM
Forecaster
Daniel Krueger
Avalanche risk The Bottom Line

The avalanche danger is CONSIDERABLE above 2,500′ due to strong northwest winds yesterday and forecast for today that will be creating fresh wind slabs. These can be 1 to 2′ deep and easy to trigger on slopes that are loaded by the wind. Although an avalanche is less likely, evaluate wind loaded slopes at mid elevations as well. Additionally, give cornices a wide berth and look out for wet loose avalanche activity on sunny, steep, south facing slopes.

SUMMIT PASS: Wind slab avalanches are a concern in the Summit area as well as strong northwest winds are expected to pick up throughout the day. There is also a buried weak layer 1-2′ deep that is still a problem to be aware of. If a wind slab is triggered it has the potential to step down into this layer, creating a larger slide. Extra caution is recommended.

SEWARD/LOST LAKE:  Strong northwest outflow winds are expected through today and into the remainder of the week. Natural wind slab avalanches remain likely in this area.

Wed, February 28th, 2024
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
1 - Low
Avalanche risk
Thu, February 29th, 2024
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
1 - Low
Avalanche risk
Thu, February 29th, 2024
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
1 - Low
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

Although no avalanches were reported yesterday it is still likely that small wind slab avalanches did release on wind loaded features at higher elevations. The last known avalanches were natural wind slab avalanches caused by strong westerly winds at higher elevations over the weekend. These are similar conditions to what we are expecting today. If you see an avalanche, it would be awesome if you snap a photo and send it to us.

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

Fresh wind slabs will be our main concern today as ridgetop winds form the northwest picked up yesterday afternoon and are forecast to gust 30+ mph today. These winds are coming from the opposite direction as the east winds that arrived with Monday’s storm. This is important to keep in mind as fresh wind slabs will likely be on different slopes that were not loaded by Monday’s easterly storm winds. Blowing snow, stiff snow over soft snow, and cracks shooting from beneath you are all good indicators you are traveling on a wind loaded slope. Areas that typically get loaded are below ridges, rollovers, and in cross loaded gullies. At mid elevations the snow may be spared by the winds making them a good choice to reduce the likelihood of triggering a wind slab avalanche.

Cornices: There was a large avalanche triggered by a cornice fall near Kickstep in Turnagain Pass. Although it is uncertain when this occurred, nature is telling us that in some place’s cornices are reaching there breaking point. If you are traveling in cornice country give them an extra wide berth as they may need just a little more weight to break off, potentially triggering a slab below.

Sun Effect: The sun is back and with that wet loose avalanches will be possible, especially on steep south facing slopes near rocks and vegetation. These also have the potential to trigger a wind slab below. The sun warming the snow can also make wind slabs easier to trigger. Although temperatures are supposed to be cold today, we are approaching the season where solar triggered avalanches will become more common.

Winds transporting snow over ridges and across gullies on the south end of Seattle Ridge. Photo 2.27.2024

Small rollerballs on steep south facing slopes seen here just above the snowmachiners helmet. Photo 2.27.2024

 

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

A layer of faceted snow buried 1.5′ to 3′ deep has been showing signs of gaining strength in snowpits in the Turnagain Pass area.  We are still keeping track of this layer because it is hard to predict how unstable a facet layer is across our forecast zone. Elevations between 2,000′ to 3,000′ have been the most concerning. The most concerning areas for this weak layer are around Summit Pass and the central Kenai Mountains, south of our forecast zone. Although it is unlikely, keep in mind that persistent layers may offer no red flags or warning signs until they have fractured into a large avalanche.

 

 

Weather
Wed, February 28th, 2024

Yesterday: Mostly sunny skies with valley fog in the morning. Moderate winds at mid elevations with gusty northwest winds (20+ mph) on the ridgetops. Temperatures remained in the mid-teens.

Today: Partly cloudy skies with valley fog are forecast for Turnagain. Ridgetop winds from the northwest will remain steady (10 to 20 mph) with 30+ mph gusts. Northwest gusts (45+mph) are expected near Seward and Whittier as gap winds increase near the coast. Temperatures are trending colder with a high of 10 F to -5 F.

Tomorrow: A few clouds with valley fog breaking up in the afternoon. Winds from the west averaging 10 mph with 20+ mph gusts are forecast around Turnagain. Gap winds are expected to bring twice as much wind from the west near Seward and Whittier. Temperatures will remain between 5 F and -10 F.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 6 0 0 91
Summit Lake (1400′) 9 0 0 47
Alyeska Mid (1700′) 8 0 0 92
Bear Valley – Portage (132′) 17 0 0
Grouse Ck (700′) 9 0 0 67

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) -3 NW 5 21
Seattle Ridge (2400′) 3 NW 3 12
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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.