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ARCHIVED - Forecasts expire after 24 hours.
Issued
Fri, March 24th, 2023 - 7:00AM
Expires
Sat, March 25th, 2023 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger is CONSIDERABLE above 1,000′. Dangerous avalanche conditions remain. Gusty northwest winds should be strong enough to create new wind slabs on top of the 3-6+ feet of snow from the past 8 day storm cycle. New wind slabs should be in the 1-2′ deep range and could release naturally. They could  also trigger a much larger slab that breaks under all that storm snow (3-6+’ deep). Additionally, that thick layer of storm snow is still adjusting to the weaker snow under it and human triggered large slabs remain possible. This would create a very large and potentially deadly avalanche. The danger is MODERATE below 1,000′ where several mid storm crusts are helping to stabilize these low elevation slopes.

We continue to recommend a cautious mindset and steering clear of steep large slopes. Sticking to mellow terrain, slopes 30 degrees or less and staying out from under steep slopes is a good way to enjoy the new snow.

SUMMIT LAKE:  Strong winds are forecast for this zone as well, adding to the dangerous avalanche conditions that currently exist. Only around 2′ of snow fell over the past 8 days, yet this is sitting on various layers of buried weak snow and large human triggered avalanches can still happen, as did last week on Templeton.

SEWARD / LOST LAKE / SNUG HARBOR:  Similar to Turnagain, this area has seen several feet of snow and dangerous avalanche conditions are expected. Strong winds will add to this issue today and natural avalanches are possible.

Special Announcements

Turnagain Pass Avy Awareness Day – Rescheduled for tomorrow.
We will be assessing parking lot conditions today to be sure adequate and safe parking is available. Cross your fingers!! This event is for everyone, skiers, boarders, snowmachiners, etc – test your beacon skills, eat some hotdogs, and shoot the breeze with us! Details: Turnagain Pass Avalanche Awareness Day – March 25th! Check back today (Mar 24) after 5pm in case we need to cancel.

Fri, March 24th, 2023
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. Dangerous avalanche conditions. 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

Skies cleared just enough yesterday to see some of the aftermath of Wednesday’s storm. It was no surprise to see many small to very large slabs in the region. The largest avalanches seen so far in Turnagain Pass were in the upper Pete’s drainage (released during the storm) and one reported late in the day yesterday on the NW shoulder of Magnum that sent debris between Magnum and Sunburst and possibly triggered other slabs (no photos). This avalanche on Magnum is thought to have occurred during the hot evening hours due to sunshine. We will try to get a look at it today; big thanks to Amanda for sending us that info. Other areas with big slabs were in Portage and Placer valleys. Otherwise, many of your garden variety storm snow avalanches were seen, some photos below. Note: many areas remain a mystery.

Mid-slope storm slabs on the northern face of Sunburst. Likely released at the tail end of Wednesday’s storm. Photo from day after on 3.23.23 by Travis Smith. 

 

Large slab on corner of Portage and Placer Valleys. 3.23.23

 

Moist to wet loose snow avalanches in the afternoon due to solar warming yesterday, Thursday, 3.23.23. This is south facing terrain across from Silvertip on the south side of Turnagain Pass.

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

After all that snow fell from the 8 day storm cycle, it looks like the northwest outflow winds will follow up today. We are expecting ridgetops to see winds in the 20-30mph range with stronger gusts. As is often the case, Turnagain Pass (especially the non-motorized east side) can be somewhat sheltered. The non-motorized side can see southerly winds below 3,500′ in these events interestingly enough. That’s because the terrain forces the wind back around to Turnagain Arm. The strongest northwest winds however should be in the usual areas like Crow Pass, Portage Valley and down to Summit Lake and Lost Lake.

With so much loose snow on the surface, wind slabs should form quickly and may release on their own. Watch for pluming in the mountains from the road and avoiding any area seeing active wind loading is a good idea. Because there is also a less likely but more concerning issue deeper in the snowpack, under all the storm snow (see Problem 2 below), we are advising folks to stick to mellow terrain. This would be slopes 30 degrees or less and staying out from under large steep slopes.

Avalanche Problem 2
  • 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

Final snowfall totals from March 15 (after the 2 week dry spell in early March) until the end of the storm cycles on March 22nd, were 70-100″ of snowfall depending on what side of the Pass (more on the north end, less on the south end). Wow! The Turnagain Pass SNOTEL station reported 7.8″ of SWE (water weight). This is a lot of load for those old early March surfaces. As we’ve been talking about, those were sun crusts on solar aspects and facets with wind hardened snow on shady aspects. We have some evidence that those old surfaces are not completely bonding like we want them to; both at the mid elevations as well as the higher elevations. This is concerning.

The big question is how likely is it really that a person, a wind slab, or solar loading (daytime heating by the sun), can trigger a huge avalanche, 3-6+ feet deep, that breaks on those old early March surfaces. We know this happened at Summit Lake last Monday where only 2′ of storm snow fell. We are also keen to know what that reported NW shoulder of Magnum looks like as we know from a photo there was no avalanche there as of 1pm yesterday. This would mean that the slope was so close to failure that it only took some warming by the sun to trigger it – scary. Because we still have very limited information and a high degree of uncertainty we continue to recommend playing it safe and avoiding large terrain and steep slopes.

Weather
Fri, March 24th, 2023

Yesterday:  Broken skies, with some sunshine poking through, were over the region post storm. Ridgetop winds were light from the northwest (~5mph) with a few stronger gusts. A few snow flurries were seen that didn’t amount to anything measurable. Temperatures warmed to the mid 30’s at the mid and lower elevations with the ridgetops staying in the mid 20’sF.

Today:  Mostly cloudy skies with a few snow flurries are expected. At most an inch could fall. Temperatures have cooled overnight to near 20F (teens along the high terrain) and ridgetop winds are bumping up. The winds are forecast to blow 20-30mph from the northwest through the day and into tomorrow morning.

Tomorrow:  Mostly clear skies, cooler temperatures, and continued northwest winds are expected tomorrow. The winds may start dying down midday – but we’ll have to see. Mostly sunny skies are forecast for Sunday as well with lighter northwest winds and a bit warmer temeratures.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 27 0 0 109
Summit Lake (1400′) 22 0 0 50
Alyeska Mid (1700′) 27 trace trace 99
Bear Valley – Portage (132′) 30 trace trace

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 19 W 7 21
Seattle Ridge (2400′) 25 N 4 10
Observations
Recent Observations for Turnagain Pass
Date Region Location
11/16/23 Turnagain Observation: Tincan Common
11/14/23 Turnagain Observation: Sunburst/Magnum
11/14/23 Turnagain Observation: Seattle Ridge
11/13/23 Turnagain Avalanche: Tincan Trees
11/12/23 Turnagain Observation: Sunburst
11/12/23 Turnagain Avalanche: Goldpan – avalanche
11/11/23 Turnagain Observation: Tincan Common
11/11/23 Turnagain Observation: Taylor Pass – Sunburst
11/10/23 Turnagain Observation: Tincan
11/10/23 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.