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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sun, February 4th, 2024 - 7:00AM
Expires
Mon, February 5th, 2024 - 7:00AM
Forecaster
Andrew Schauer
Avalanche risk The Bottom Line

The avalanche danger is CONSIDERABLE above 2500′. New snow and strong winds overnight will make it easier to trigger an avalanche where another round of wind slabs have formed. There is also still a chance that you could trigger a deeper avalanche on the older wind slabs that formed near the end of last week, which buried a weak layer of snow. The danger is MODERATE below 2500. You may still encounter reactive wind slabs, but they should be smaller and harder to find at and below treeline. We’re also still paying close attention to the ongoing glide cycle and avoiding spending time below open glide cracks.

Special Announcements

Chugach State Park: The National Weather Service has issued a Winter Weather Advisory through noon today for areas including the Chugach Front Range because of the new snow and gusty northerly winds.

SnowBall 2024:  Mark your calendars for Valentine’s Day, Feb 14 (7-11pm @ 49th St Brewing). The evening promises costumes, finger food, a rocking band, silent auction, and of course plenty of great company. Join us in supporting Chugach Avy as well as our friends at the Alaska Avalanche School. Details and tickets HERE.

Sun, February 4th, 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
Mon, February 5th, 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
Mon, February 5th, 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
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

There were no new avalanches reported yesterday, but we did receive more information about an avalanche a snowboarder triggered in the Library on Tincan Ridge on Friday. The avalanche was roughly 100 feet wide and 12″ deep, and it failed on a slope that had been recently loaded by strong winds the previous day. The person was caught and carried, but was able to ride away uninjured. Thank you to the person involved for sharing details in this observation.

POV moments after the avalanche was triggered. Photo shared anonymously, 02.02.2024.

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

We’ve received around 2-6″ new  snow with strong easterly winds over the past 24 hours, and we are once again concerned with the good chance that a person will be able trigger an avalanche on wind-loaded slopes. Today’s wind slab problem may be trickier than other days when wind slabs are the main concern, since there have been multiple wind events out of different directions that formed slabs over the past week that may still be reactive today. The most sensitive snow will be the new snow that fell and blew around in the past 24 hours, and that is expected to produce avalanches up to a foot deep in the alpine. In addition to these fresh slabs, we are also still thinking about the aftermath of last week’s outflow event, which formed slabs on a weak layer of faceted snow that may still be reactive today. Check out the video of Friday’s snowboard-triggered avalanche in the Library included below for a sense of the size and potential consequences of triggering one of these avalanches.

The layering of these problems may be a little tricky to identify, but the terrain that harbors them should be consistent. Be extra cautions around steep terrain just below ridgelines, convexities, or steep gullies. The older slabs that formed at the end of the week may be a little harder to identify now that they have a few inches of fresh snow on top, so the best bet is to treat any of those pieces of terrain with caution. With strong winds out of multiple directions over the past three days, we should be paying attention to these terrain features on all sides of the compass. Pay close attention to signs like shooting cracks or collapsing as clear indications that the snowpack is unstable and capable of producing an avalanche. Even in the absence of these signs, the combination of stiff snow sitting on top of softer snow is the recipe we are expecting to produce avalanches today.

Shooting cracks like this are a clear sign that the snowpack could produce an avalanche in steep enough terrain. Photo from the Crow Creek area 02.03.2024

 

Avalanche Problem 2
  • Glide Avalanches
    Glide Avalanches
  • Aspect/Elevation
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
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.

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’re still concerned with the possibility of encountering a large and destructive glide avalanche. It has been a few days since the last glide avalanche was reported, but the behavior of this type of avalanche is really hard to predict and we have seen an unusually active cycle for over a month now. Luckily it can be easy to manage this problem by looking for and avoiding slopes with open glide cracks on them. Now that we have seen a few storm events, an active glide crack may be a little harder to recognize. It may look like a brown frown where the snowpack has moved enough to expose bare ground, or it may look like a rumpled or cracked surface if the crack has been buried by new or windblown snow.

Multiple glide cracks on the front side of Eddie’s ridge. Photo taken ahead of last week’s storm, 01.27.2024.

Weather
Sun, February 4th, 2024

Yesterday: We saw clear skies and light westerly winds yesterday morning, with increasing cloud cover through the day and light snow in the afternoon. Winds and snow picked up overnight, and we’ve received 2 to 6” snow with east winds averaging 10 to 25 mph with gusts of 25 to 35 mph. Temperatures remained cold for most of the day with lows in the negative teens F to right around 0 F, but the cold snap has ended and stations are currently showing temperatures in the mid teens to low 20s F. The weather station on the west end of the Whittier tunnel has seen a temperature swing of 51 degrees F in just 24 hours, warming from -27 F yesterday morning to 24 F at 5 am today!

Today: Light snow is expected to continue this morning before tapering off this afternoon, with another 1 to 3” new snow expected before the system passes. We should see snow to sea level for the rest of this round of precipitation. Strong easterly winds around 20 to 30 mph should quickly back down and are expected to switch to the west at around 5 mph by this afternoon. High temperatures are expected in the upper teens to 20 F, with lows tonight in the mid teens F.

Tomorrow: Another round of snow showers is expected tomorrow, with another 2 to 3” expected through the day. We may see some rain up to around 300 feet or even a little higher closer to the coast for tomorrow’s storm. Winds will pick up again out of the east with average speeds of 15-25 mph and gusts of 20 to 30 mph. High temperatures are expected in the low 20s F with lows in the high teens to low 20s F.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 6 2 0.2 80
Summit Lake (1400′) -1 3 0.3 N/A
Alyeska Mid (1700′) 7 6 0.3 85
Bear Valley – Portage (132′) -2 3 0.3
Grouse Ck – Seward (700′) 6 1 0.2 56

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 13 ENE 12 36
Seattle Ridge (2400′) 7 SE 12 22
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.