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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sun, February 25th, 2024 - 7:00AM
Expires
Mon, February 26th, 2024 - 7:00AM
Forecaster
Andrew Schauer
Avalanche risk The Bottom Line

The avalanche danger is CONSIDERABLE above 2500′ and MODERATE above 1000′. Northwest outflow winds increased last night and are expected to continue this morning, making natural avalanches possible and human-triggered avalanches likely where the wind is loading snow into steep terrain. There is also a smaller chance that you may be able to trigger a bigger avalanche on a weak layer of snow buried 1-3′ deep. The danger is LOW below 1000′.

 

SNUG HARBOR/LOST LAKE/SEWARD: These southern areas have received the most snow over the past week, and are expected to see the strongest outflow winds today. Expect dangerous avalanche conditions with large natural and human-triggered avalanches likely in wind-loaded terrain in these areas today.

Special Announcements

Chugach State Park: Dangerous conditions also exist in CSP. This area was favored by this most recent storm, and that new snow is not expected to bond well to old surfaces. Natural and human-triggered avalanches are likely today, and we recommend a cautious mindset if you plan on getting out in this area.

The National Weather Service has issued a Winter Storm Watch that covers our advisory zones for a storm that is expected to impact us tomorrow.

John Mtn Avalanche Accident Report: The full accident report for the recent avalanche fatality on John Mtn is now posted on our accidents page.

Sun, February 25th, 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
Mon, February 26th, 2024
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
Mon, February 26th, 2024
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

We watched a natural avalanche in steep northeast-facing terrain that was being actively wind-loaded yesterday afternoon on Bench Peak.  Visibility was limited, so we don’t have a great idea of the extent of natural activity from the past 24 hours but we can expect there was other similar activity across the forecast area yesterday.

We watched an avalanche run through this steep northeast-facing terrain as the wind was blowing just after this photo was taken. 02.24.2024

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

Today is the kind of day where avalanche accidents happen. After a week of mostly stormy or cloudy weather, clouds are expected to break up and we will finally be able to get up into the alpine. The low-density snow that we’ve gotten this week is being blown into sensitive wind slabs right now, and it will be easy to trigger an avalanche in steep, wind-loaded terrain today. The winds are expected to die down through the day, but the recently formed wind slabs will remain reactive all day. So despite benign weather, it will remain likely that a person will be able to trigger an avalanche especially above treeline.

If you are getting out to enjoy this break in the stormy weather – and we hope a lot of people are – remember that there is still a good chance that you will be able to trigger an avalanche on wind-loaded slopes. The most likely places to run into trouble will be in steep terrain just below ridgelines, convex rolls, or in wind-loaded gullies. For slopes that are sheltered from the outflow winds, loose snow avalanches (sluffs) will be easy to trigger and may pick up a large volume of snow. These protected slopes will have the best surface conditions and the safest avalanche conditions, as long as you avoid getting caught in your sluff.

Now that it is already late February, the sun will start to have a noticeable effect on snow surfaces. With cooler temperatures and moderate winds expected, snow surfaces should remain dry for most slopes. But keep an eye out for natural loose avalanches in steep southerly terrain that is heating up in the sun through the day.

The most recent storm snow fell on a stout crust up to around 1800′ elevation. Wind slabs and dry loose avalanches will slide easily on this smooth bed surface. 02.24.2024

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

The weak layer of faceted snow that formed during January’s dry spell is still on our radar. It is now buried anywhere from 1-3′ deep, and is most concerning at elevations between 2000′ and 2500′. The good news is that we are seeing signs that it is gaining strength across the advisory area, and we think at this point it is unlikely a person will be able to trigger an avalanche on this layer. That said, we are still paying close attention to it. The layer is tricky to assess since it is now buried deep enough that travel tests like hand pits and test slopes won’t give you reliable feedback. The only way to truly assess the layer is to take the time to dig a pit and look for a weak layer of sugary snow in the upper 3′ of the snowpack. This layer is becoming harder to find, which is a good thing. But it might still be reactive on isolated slopes, and is worth keeping in mind while choosing where you want to travel today.

 

Weather
Sun, February 25th, 2024

Yesterday: We received 2-4” low density snow equaling 0.1-0.3” snow water equivalent (SWE), and snow to sea level. Skies were cloudy with westerly winds of 5 to 15 mph and gusts of 25 to 35 mph. High temperatures were in the upper teens to upper 20s F and lows were in the mid teens to mid 20s F.

Today: We should see mostly sunny skies with cool temperatures in the mid to upper teens F today, dropping into the single digits F tonight. Outflow winds picked up last night and are expected to slowly taper off through the day, with average speeds of 10 to 30 mph and gusts of 20 to 40 mph. We may see some lingering valley clouds, but no precipitation is expected today.

Tomorrow: A quick but strong system is on the way tomorrow. Easterly winds will pick up ahead of the snow, with average speeds of 30 to 50 mph and gusts of 40 to 60 mph. The snow isn’t expected to arrive until late afternoon, with only a trace to 3” likely for most places during the day, but 8-18” possible Monday night into Tuesday morning and snow to sea level likely. Stay tuned to see how it develops.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 21 1 0.1 89
Summit Lake (1400′) 22 3 0.3 49
Alyeska Mid (1700′) 21 4 0.2 96
Bear Valley – Portage (132′) 28 2 0.25
Grouse Ck (700′) 26 3 0.2 70

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 11 WNW 9 34
Seattle Ridge (2400′) 15 NNW 10 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.