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ARCHIVED - Forecasts expire after 24 hours.
Issued
Tue, January 17th, 2023 - 7:00AM
Expires
Wed, January 18th, 2023 - 7:00AM
Forecaster
Andrew Schauer
Avalanche risk The Bottom Line

The avalanche danger is CONSIDERABLE at all elevations. Last night’s storm brought around a foot of new snow along with strong easterly winds, forming touchy slabs on top of a snowpack with multiple weak layers. It is likely a person can trigger an avalanche in the upper 1-2′ of the snowpack, and possible to trigger a very large avalanche on a weak layer buried 3-6′ deep or deeper. Cautious route finding is essential, which means avoiding traveling on or below steep avalanche terrain.

If this storm continues longer than expected into today, be aware of continued increasing avalanche danger, with the potential for conditions to approach HIGH danger if we continue to see strong winds and heavy snowfall through the day.

Special Announcements

There will be intermittent traffic delays for avalanche hazard reduction on Tuesday January 17, 2023 (today), on the Seward Highway from mile post 88 to 85 South of Girdwood from 9:00 am to 400 pm. Motorists should expect delays of 45 minutes or longer. Updates will be posted on the 511 system.  http://511.alaska.gov/

Forecaster Chat #2:  Join us at the Girdwood Brewing Co. from 5:30-7:00 p.m. on Thursday, Jan. 19! CNFAIC forecaster Andrew Schauer will open the night with an overview of the state of the snowpack, followed by a discussion on how safe terrain management changes depending on the type of avalanche problem at hand. More details here.

Tue, January 17th, 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. 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

Multiple groups reported small avalanches yesterday, with activity noted in the Seattle Ridge flats, Eddie’s, and Tincan. Two of the avalanches were human-triggered (one skier, one snowmachine), and all of them appear to be failing on the layer of surface hoar that was buried on 1/10. These avalanches were small; the size seems to be limited to the small but steep terrain features where they are occurring. At least one avalanche was triggered remotely from low-angle terrain adjacent to the slope that slid.

Remote-triggered avalanche in the Tincan Trees yesterday. Photo: Jeff Levin

Avalanche Problem 1
  • Storm Slabs
    Storm Slabs
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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

Last night’s storm came in stronger than expected, bringing around a foot or more of snow equaling 1-1.5″ of snow water equivalent (SWE). This came along with strong easterly winds blowing 15-30 mph and gusting 30-45 mph at upper elevations. The storm is expected to taper off by late this morning, but the danger will remain elevated through the day. This new snow is loading a snowpack with two known weak layers, making for dangerous avalanche conditions.

The most likely avalanches will be failing within new and wind-loaded snow, or on the layer of surface hoar that is buried just below the old snow surface. This layer has produced avalanches the past two days, and will remain reactive today with the new load of snow from last night. So far, the avalanches triggered on this layer have been small, but after last night the layer is now buried 1-2′ deep in sheltered terrain, and up to 2-4′ deep on wind loaded slopes, making it capable of producing larger and more dangerous avalanches. For today, it is likely a person could trigger an avalanche large enough to get fully buried and cautious terrain use is really important. Avoid travelling on or below steep terrain. It is possible to trigger an avalanche remotely (as seen from the skier-triggered avalanche on Tincan yesterday), so be aware of the potential for triggering an avalanche on steeper slopes that are connected to lower-angle terrain. An avalanche triggered within the new snow or on that layer of buried surface hoar may step down to the deeper crust/facet weak layer that is now 3-7′ deep. More on this in problem 2 below.

This round of snow and wind should start wrapping up later this morning. If the active weather continues later into the day, and we continue to see storm totals stacking up with winds blowing the snow around, we can expect to see the danger continue to rise. As always, pay attention to changing conditions, and be prepared to seriously dial back your terrain exposure if the storm continues longer than expected.

 

Snowmachine-triggered avalanche 6-12″ deep in the Seattle Ridge flats yesterday. This layer now has another foot of snow on top of it, and will remain a concern today. 01.17.2023

 

Avalanche Problem 2
  • Deep Persistent Slabs
    Deep Persistent Slabs
  • 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.

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

It’s been 10 days since the last avalanche was triggered on the Thanksgiving crust/facet layer, but it still remains a concern. This most recent loading event is adding some stress to the snowpack, but it is really uncertain whether it will be a big enough load to make that deep weak layer more reactive today. Deep slab problems are notoriously hard to predict, and this layer has shown its potential for making really big avalanches. When the uncertainty is high and the consequences are even higher, the only option to manage the problem is by staying really conservative with your terrain choices. With the combination of this deeper weak layer and the surface problems mentioned in Problem 1 above, we should be avoiding steep slopes for now.

That’s a setup that I don’t want to mess with. Sticking to low-angle terrain for now. Snowpit from Eddie’s, 01.15.2023.

Weather
Tue, January 17th, 2023

Yesterday: Skies were mostly cloudy with temperatures in the mid 20’s to low 30’s F. Winds backed off slightly during the day, but have been blowing 15-30 mph with gusts of 30-45 mph since yesterday afternoon. As of 6:00 a.m. we’ve received around 1″ snow water equivalent, equal to about a foot of snow. The snow line has been around 500′.

Today: We should see another 1-3″ of snow before things shut down later this morning. Winds are expected to back off as the precipitation tapers down, with average speeds around 20-25 mph this morning calming to 5-10 mph by later in the afternoon. Temperatures are slowly dropping and should be in the upper 20’s F during the day, with overnight lows in the upper teens to low 20’s F.

Tomorrow: It is looking like a quiet day weather-wise tomorrow, with mostly cloudy skies and high temperatures in the mid 20’s F. Winds should be around 5-15mph with gusts of 10-25 mph out of the east. The next round of precipitation should begin tomorrow night, with 2-4″ possible by Thursday morning. The weather has been challenging to predict the past two weeks, so be sure to stay tuned for more.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 31 12 (est.) 1.0 66 (est.)
Summit Lake (1400′) 29 1 0.1 32
Alyeska Mid (1700′) 31 15 0.97 68
Bear Valley – Portage (132′) 36 rain 1.09

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 22 ENE 21 42
Seattle Ridge (2400′) 26 SE 7 19
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.