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ARCHIVED - Forecasts expire after 24 hours.
Issued
Mon, February 12th, 2024 - 7:00AM
Expires
Tue, February 13th, 2024 - 7:00AM
Forecaster
Andrew Schauer
Avalanche risk The Bottom Line

The avalanche danger is CONSIDERABLE above 1000′. Very strong easterly winds will increase the chances of triggering a large avalanche where snow is being blown into sensitive slabs, and we will most likely see some  natural avalanches as the winds pick up. This will be adding stress to a deeper layer of weak snow that has the potential to make larger avalanches. Another day of dangerous avalanche conditions will mean another day of cautious route finding, sticking to low angle terrain for now until things can settle out. The danger is MODERATE below 1000′, where you may find the same avalanche problems but triggering an avalanche will be a bit less likely.

ROOF AVALANCHES: Be on the lookout for increased chances of roof avalanches with rain expected in town today and tonight. Be mindful of where you park vehicles, keep your eyes up when you are entering and exiting buildings, and keep an eye on kids and pets.

Special Announcements

Chugach State Park:  The National Weather Service has issued a High Wind Watch for the Anchorage Hillside, in effect this afternoon through tomorrow morning.

SnowBall 2024 is almost here! This 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. Join us in supporting Chugach Avy as well as the Alaska Avalanche School. Details and tickets HERE.

Mon, February 12th, 2024
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
Tue, February 13th, 2024
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
Tue, February 13th, 2024
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. 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

The most recent avalanches that we know of were a skier-triggered avalanche on Eddie’s Ridge and two snowmachine-triggered avalanches on the back side of Seattle Ridge Saturday. These look to have failed roughly 2 to 3 feet deep, likely on the January facet layer that we are concerned about.

The crown of this skier-triggered avalanche was roughly 2-3’deep and 80′ wide. Heavy wind loading today will increase the chances of triggering a similar avalanche today. Photo: Rafael Pease, 02.10.2024.

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

Stormy weather returns today, but unfortunately it’s looking like the wind will be the main event. Easterly winds are expected to quickly increase to 30 to 50 mph with gusts of 40 to 60 mph through tonight. Along with the winds we could see another 1 to 3″ snow in most parts of our advisory area during the day, with the exception of the more coastal areas like Portage, Placer, and Seward, which will likely see more like 3 to 6″ during the day and over a foot of snow by tomorrow morning. Warming temperatures will bring the rain line up to around 1400′ this evening.

That active weather will increase the chances of natural and human-triggered avalanches today. Several hours of winds near 50 mph would have us concerned regardless of the snowpack, and that weak layer that formed back in January is going to make things even worse (more on that in Problem 2). Expect to find dangerous avalanche conditions in the mountains today, and be aware of the potential for overhead hazard as the likelihood of natural avalanches increases through the day. For now, we are still planning on sticking to low-angle terrain and trying to limit time spent in runout zones below steeper avalanche paths.

Cornice Fall: Warmer temps and strong winds will likely make giant cornices over the next couple days. These may fail without notice, and can be a very efficient trigger for a large avalanche. Be aware of this additional hazard, and avoid spending time under them.

The wind was already at work blowing snow yesterday, and it will be picking up today. Photo of Raven Ridge in the Summit Pass area by Heather Thamm, 02.11.2024

Avalanche Problem 2
  • Persistent Slabs
    Persistent Slabs
  • Aspect/Elevation
  • 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.

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

As mentioned above, we’re still concerned with the potential for triggering a larger avalanche failing on weak snow buried about 2 to 3 feet deep. This weak layer formed during the three-week dry spell in January, and it is slow to heal. We’ve seen it in all of our snowpits in Girdwood, Placer, Turnagain, Summit, and Seward, and we have found it to be the weakest and most developed between around 1000 to 2000′ elevation. This layer will likely heal with time but another major loading event on the way today will be adding stress and pushing it closer to making avalanches. Keep this dangerous setup in mind if you are trying to find sheltered snow at lower elevations today– the terrain with the best snow on the surface may also be the most likely place to trigger an avalanche on that deeper weak layer. This was likely the culprit for Saturday’s skier-triggered avalanche on Eddie’s Ridge, and we think it will still produce more avalanches before it heals.

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

It has been a little over two weeks since we last saw a glide avalanche, and we’re starting to think the glide cycle may have gone dormant for now. However, we don’t have any way to predict these massive avalanches so the best practice is still to avoid spending any time under open glide cracks. The series of storms over the past week has made these harder to recognize, which also adds the hazard of falling into a concealed glide crack. Pay careful attention the snow surface, and avoid traveling on or below slopes with exposed cracks or an unusually wrinkled texture.

Weather
Mon, February 12th, 2024

Yesterday: We saw a brief break in the active weather during the first part of the day, with partly cloudy skies and light easterly winds. The weather picked up in the afternoon with winds out of the east at 15 to 25 mph gusting to 35 to 50 mph and most stations showing 2 to 4” snow with mixed precipitation at sea level. High temperatures were in the low 20s to low 30s F with lows in the upper teens to upper 20s F.

Today: Easterly winds are expected to pick up this morning, with sustained speeds of 30 to 50 mph and gusts of 40 to 70 mph likely through tonight and into tomorrow. Most areas are expected to see only 1 to 3” snow today, with the exception of coastal areas like Portage and Seward which will likely see double those totals today and possibly over a foot of snow by tomorrow morning. Temperatures are expected to rise into the upper 20s to mid 30s F during the day and stay there through the night. With those rising temperatures we may see rain up to 1400’.

Tomorrow: Strong easterly winds are expected to continue tomorrow, with sustained speeds of 25 to 40 mph and gusts of 30 to 50 mph. Precipitation should finish tomorrow morning for most zones, although it is looking like it may stick around longer in the Portage and Placer valleys with another 2 to 5” snow during the day. The rain line should drop back down to around 600 to 800’ as precipitation tapers off, with daytime temperatures in the mid 20s to low 30s F and lows in the md to upper 20s F overnight.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 26 4 0.3 89
Summit Lake (1400′) 31 0 0 43
Alyeska Mid (1700′) 27 2 0.18 92
Bear Valley – Portage (132′) 34 2 0.43
Grouse Ck (700′) 31 1 0.2 62

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 18 ENE 15 51
Seattle Ridge (2400′) 22 N/A N/A N/A

Seattle Ridge anemometer has not been reporting wind data in the past 24 hours.

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.