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ARCHIVED - Forecasts expire after 24 hours.
Issued
Tue, February 13th, 2024 - 7:00AM
Expires
Wed, February 14th, 2024 - 7:00AM
Forecaster
Wendy Wagner
High Avalanche Danger
Travel in avalanche terrain is not recommended. Avoid being on or beneath all steep slopes.
Avalanche risk The Bottom Line

Very strong east winds are impacting the mountains and raising the avalanche danger to HIGH at the mid and upper elevations. Naturally occurring wind slab avalanches are likely and human triggered avalanches are very likely on any wind loaded slope. Travel in avalanche terrain is not recommended during this stormy and windy weather, including runout zones under large avalanche paths.

Although it’s raining below 1,000′, the danger is CONSIDERABLE in avalanche paths due to avalanches that may occur above.

ROOF AVALANCHES: Watch for snow to continue to slide off roofs due to rain and warm temperatures.

Special Announcements

Chugach State Park:  Dangerous avalanche conditions exist due to very strong easterly winds. A large natural avalanche occurred in the South Fork of Eagle River yesterday that deposited up to 7 feet of debris onto the Hiland Road around mile 7. No people, cars, or structures were reported to be involved. The CSP Avy Specialist happened to be in the area at the time and was able to get some photos and information.

The National Weather Service has issued a High Wind Watch for the Anchorage’s Front Range, in effect until 9pm tonight.

Tomorrow – SnowBall 2024!! Join us Wednesday- 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 while supporting Chugach Avy and the Alaska Avalanche School. Details and tickets HERE.

Tue, February 13th, 2024
Alpine
Above 2,500'
4 - High
Avalanche risk
Treeline
1,000'-2,500'
4 - High
Avalanche risk
Below Treeline
Below 1,000'
3 - Considerable
Avalanche risk
Wed, February 14th, 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
Wed, February 14th, 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

We are unaware of any confirmed natural or human triggered avalanches in our forecast area from yesterday. That said, behind the clouds there were probably several natural wind slabs that released due to the sustained strong east winds. We did get reports of collapsing in the snowpack in the mid elevations on Center Ridge and Tincan.

Avalanche Problem 1
  • Wind Slabs
    Wind Slabs
  • 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.

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

If you thought the winds were strong yesterday, wait for today. This weather event is producing significantly strong easterly winds region-wide with not a lot of snow, interestingly enough. Snowfall over the past 36 hours has added up to 4-8″ at Turnagain and 6-10″ in Girdwood, another 1-3″ is expected today. Sustained winds along the ridgetops are currently 25-40 mph with gusts between 50 and 90 mph. The peak in wind is expected midday today. That means even stronger winds could develop. Either way, the wind is by far the major contributor to the increase in avalanche danger.

Sunburst (Turnagain ):    Max gust 83 mph
Max’s Mtn (Girdwood):  Max gust 87 mph

Wind Slab Avalanches:  Naturally occurring wind slab avalanches are likely happening now and should continue through the day. These slabs could be several feet deep, break in older weak layers making the avalanche larger, and run further than expected. Also note, winds could be getting into the mid elevations and loading slopes that don’t usually see wind loading. It’s one of those days that the weather will most likely keep many of us out of the mountains or in sheltered areas outside of avalanche terrain. This is the best bet for today.

Cornices:  The warm(ish) temperatures and strong winds are likely forming new cornices and these are likely breaking off in pieces. This is a typical way wind slabs are triggered, from a piece of cornice falling onto a wind loaded slope.

Avalanche Problem 2
  • Persistent Slabs
    Persistent Slabs
  • 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.

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

Buried anywhere from 1 to 3 feet deep at this point is that old layer of sugary faceted snow that formed in January. This layer exists everywhere, but is variable as to how weak and concerning it is. It has shown to be the weakest at elevations between 1,000 and 2,000 feet. This is right in the treeline band where a lot of traffic can take place. Hence, the places we might seek out during windy weather could also produce an avalanche.

Hopefully we’ll get to see some of the aftermath of what kind of avalanches the winds were able to make. Until then, sticking to low angles well out of any avalanche path above is recommended.

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 are still a concern on any slope with glide cracks present. We have not seen or heard of one releasing into an avalanche for over two weeks now, but that doesn’t mean a crack can’t release today. Continuing to avoid time under glide cracks is prudent.

Weather
Tue, February 13th, 2024

Yesterday:  Strong winds, cloudy skies, and varying degrees of snow fell above 1,000′ yesterday. The rain/snow line hovered near 1,000′. Portage/Placer Valleys received around 12-18″ while Turnagain Pass only saw a few inches. Ridgetop winds have been very strong averaging 25-35 mph with gusts near 85 mph. Temperatures are still warm, 20s to upper 30s F.

Today:  Strong winds will continue today with another few inches of snow falling above 1,000′, rain below. Sustained winds should be 25-40 mph with gusts nearing 90 mph from the east/southeast. Temperatures look to cool slightly, bringing snow levels down to around 500′ by this evening.

Tomorrow:  A couple more days of this very strong east wind is expected with only minimal amounts of precipitation. Both Wednesday and Thursday are looking to be very windy, yet skies are forecast to clear a bit, which is unusual for this wind direction. Stay tuned!

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 33 2 0.3 88
Summit Lake (1400′) 37 0 0 44
Alyeska Mid (1700′) 31 6 0.7 98
Bear Valley – Portage (132′) 38 rain 1.4
Grouse Ck (700′) 34 tr 0.4 63

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 22 ENE 37 83
Seattle Ridge (2400′) 26 SE 18 37
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.