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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sun, March 26th, 2023 - 7:00AM
Expires
Mon, March 27th, 2023 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger remains CONSIDERABLE due to the possibility of triggering large and deadly avalanches. These are slabs 3-6+ feet deep and generally give no prior signs of instability. Several were triggered remotely yesterday by people from the bottom of slopes and adjacent to them (no one caught). Warmer weather today may make these easier to trigger. Additionally, wet loose avalanches are likely to occur naturally in the heat of the day on sunlit slopes. Wet sluffs could trigger small to very large slabs below. We continue to recommend a cautious mindset and sticking to slopes 30 degrees or less with nothing steeper above. 

Low elevations near sea level:  Avoid being under steep slopes where a large avalanche occurring above could send debris. This occurred yesterday in the Skookum drainage, popular for XC skiers, fat bikers, and snowmachiners.

SUMMIT LAKE / SEWARD / LOST LAKE / SNUG HARBOR:  Dangerous avalanche conditions are suspected in these areas as well.

*Special Avalanche Bulletin*
Issued through the NWS due to these dangerous avalanche conditions.

Special Announcements

Support the avalanche forecast with Pick.Click.Give! 
Our Friends group funds 50% of our operating budget, forecaster salaries, and safety equipment to ensure professional, daily avalanche advisories all winter for the Chugach National Forest. The deadline is March 31, so follow these instructions today to support your daily avalanche forecast with your PFD!

Chugach State Park:  Dangerous avalanche conditions may exist here as well after the strong winds on Saturday. We received a report of a natural large avalanche in the South Fork of Eagle River area.

Sun, March 26th, 2023
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 was a fairly busy day in the backcountry with many folks doing their best to play it safe. Despite this, there were still many large and scary avalanches triggered. They were all remotely triggered and luckily the debris did not wash over anyone that we know of. Most of these were in Seattle Ck drainage (map). The other was in Skookum drainage near Placer Valley. We will be compiling additional photos and information today. Basic info here:

Seattle Creek (3rd Bowl):  Two snowmachiners near the bottom of the drainage triggered a collapse that then triggered two large slabs on the N and NW faces, shortly after another slab released on a SW aspect.

Seattle Creek (-3 Bowl, Triangle Bowl):  One snowmachiner lower on the slope in lower angle terrain also triggered a collapse (and small slab on a small terrain feature) that then triggered two larger slabs above and to the side, with another larger slab releasing out of view. These were on W to NW aspects.

Skookum lower drainage:  Possibly skier triggered – preliminary report here. Slab was extremely wide. Debris ran over snowmachine and possibly fat bike and xc tracks below. See photo below.

 

3rd Bowl. Northerly facing slab that was one of three slabs releasing in 3rd Bowl. Crown up to 8′ deep, maybe more in wind loaded areas. Photo by riders involved, 3.25.23.

 

3rd Bowl. The lower slab, which was the largest, that released behind the riders lower in the drainage and wrapped around to a more westerly aspect. Photo by riders involved, 3.25.23.

 

3rd Bowl: The smallest of the three slabs triggered (SW aspect). This one released last, likely sympathetically by the debris washing down from one on the other side. The debris from both slides ran together in the bottom on the drainage forming a ridge. Photo by riders involved, 3.25.23.

 

-3 Bowl/Triangle Bowl. These two slabs pulled out shortly after a rider dipped into a small terrain feature and triggered a collapse. Note the much larger slab (crown barely seen in the upper left of the photo) wraps around out of view. Tracks on slope were from another party earlier in the day. Photo by riders involved, 3.25.23.

 

Skookum drainage. Several slabs released near the same time to generate a very large avalanche with debris covering many tracks in the valley below. Unknown exact trigger, possibly skier triggered remotely. Photo from Henry Munter, 3.25.23. 

Avalanche Problem 1
  • Deep Persistent Slabs
    Deep Persistent Slabs
  • Aspect/Elevation
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and 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

The photos above say it all. We are again in a period of dangerous avalanche conditions. It’s that setup where everything seems fine until it is not. Some slopes may in fact be fine, but there is really no way to know this 100%.

All that snow from March is not bonding well in many places. There was anywhere from 5-10 feet that fell from March 15 to the 22nd, which has settled to around 3-6′, more where the winds have loaded it. These avalanches are releasing under this snow, on the old early March ‘dry spell’ surfaces (facets/hard wind packed snow on shady slopes and sun crusts with areas of facets below the crust on solar aspects). The weak layer collapsing and creating these slabs is the faceted snow. Sunshine and warming of the upper snowpack is expected today, which can make it easier for us to trigger these slabs, and even in some cases may cause them to release on their own. Wet loose avalanches or cornice falls could also trigger a big slab.

We had a lot of uncertainty with this setup the past several days, but that has changed with one clear sky day and people out testing the snowpack. It’s clear we have a problem unfortunately. This layer is too deep to test, but we have all the evidence we need at this point to be conservative. Hence, staying away from large steep slopes and paying close attention to your location under slopes is recommended.

Avalanche Problem 2
  • Wet Loose
    Wet Loose
  • Aspect/Elevation
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
Wet Loose
Wet Loose avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

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

A warm day is on tap with light westerly winds (in fact temps have been warming overnight already). We are expecting to see rollerballs and moist to wet sluffs releasing through the day. Some could be large enough to run to the bottom of slopes. As is the case this time of year, the easterly slopes will see the first warm up and by 5pm the westerly slopes will be quite warm. Wet sluffs should be easy for people to trigger once the surface becomes moist and sticky.

Sunshine may also make the wind slabs that formed yesterday more reactive. Yesterday’s NW winds formed slabs on all aspects due to terrain channeling. It’s common for a wet sluff to trigger small pockets of slabs on its way down. The more concerning issue of course is if one of these triggers a deep slab discussed above.

Cornices may start warming and becoming closer to their breaking point. Not only is a cornice fall dangerous, but it could trigger a large slab below. Give these an extra wide berth along ridgelines.

Small wet loose sluffs releasing midday yesterday in Jr’s Bowl (2nd Bowl) on the backside of Settle Ridge. 3.25.23.

 

A quick THANK YOU to everyone who stopped by the motorized parking lot yesterday for our Turnagain Pass Avy Awareness Day!!

Weather
Sun, March 26th, 2023

Yesterday:  Sunny skies with moderate to strong west to north winds were over the region. Temperatures bumped into the 30’sF at the mid elevations but stayed cool, in the teens in the Alpine.

Today:  Sunny skies are forecast again with some high clouds overhead at times. Ridgetop winds should be light, 5-10mph, from the northwest. Temperatures look to warm to near 40F at 1,000′ and to near 30F along ridgelines.

Tomorrow:  Partly to sunny skies are expected for Monday. The westerly winds look to bump back up into the 10-20mph range along the ridgelines. Warmer springtime temperatures look to remain through Monday and into Tuesday.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 19 0 0 103
Summit Lake (1400′) 19 0 0 51
Alyeska Mid (1700′) 21 0 0 95
Bear Valley – Portage (132′) 25 0 0

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 15 W 8 22
Seattle Ridge (2400′) 19 NW 8 24
Observations
Recent Observations for Turnagain Pass
Date Region Location
02/24/24 Turnagain Observation: TinCan Backdoor/ Center Ridge
02/22/24 Turnagain Avalanche: Lynx Creek
02/22/24 Turnagain Observation: Turnagain, Seattle, Mt Ascension
02/21/24 Turnagain Observation: Tincan Trees
02/21/24 Turnagain Observation: Sunburst
02/20/24 Turnagain Avalanche: Tincan
02/20/24 Turnagain Observation: Seward Highway across from Johnson Pass TH
02/19/24 Turnagain Avalanche: Base of Seattle Ridge
02/18/24 Turnagain Observation: Lynx creek
02/18/24 Turnagain Observation: Tincan Trees
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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.