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ARCHIVED - Forecasts expire after 24 hours.
Issued
Wed, February 21st, 2024 - 7:00AM
Expires
Thu, February 22nd, 2024 - 7:00AM
Forecaster
Mik Dalpes
Avalanche risk The Bottom Line

The avalanche danger is CONSIDERABLE at all elevations today. Large amounts of new and windblown snow in the upper elevations and rain falling on snow in the lower elevations will make natural avalanches possible and human triggered avalanches likely. Avalanches will be more likely in places that received greater amounts of snow like Girdwood, Portage, and Placer Valleys. Wet avalanches are possible in lower elevations where the snowpack hasn’t frozen in several days, and there is still a chance that a larger avalanche may fail on a weak layer of snow buried deeper in the snowpack. With multiple avalanche problems at different elevations, we recommend careful snowpack evaluation and choosing sheltered terrain in the treeline elevation band today.

SEWARD:  The Seward mountains received a large amount of rain (1-2″) up to at least 1,500′ yesterday and 1-2′ of snow above snow line. Dangerous avalanche conditions exist in this area.

Roof Avalanches: Watch for roofs with snow/ice remaining on them to continue shedding with the rain and warm temperatures.

Special Announcements

Chugach State Park: The National Weather Service has issued a Special Weather Statement for the Anchorage area and the mountains in the Western Chugach in our Chugach State Park advisory zone. Expect to see avalanche danger rise as winds, rain, and snow impact the area today.

AKDOT&PF  Avalanche Closure Notification: There will be intermittent traffic delays Wednesday February 21, 2024 on the Seward Highway and Portage Glacier Highway for Avalanche Hazard Reduction work from mileposts 88 to 82 on the Seward Highway, South of Girdwood and near milepost 5 and Bear Valley on the Portage Glacier Highway. Motorists should expect delays of up to 45 minutes between 09:00 AM and 1:00 PM. Updates will be posted on the 511 system at http://511.alaska.gov/.

Friday night in Seward!
Forecaster Chat, 5-6 pm at the Community Library and Museum room
. For our friends in Seward and Moose Pass, come chat with us about the product we are producing called the “Weekend Avalanche Outlook”. We’ll also be talking about the state of the snowpack in Summit and Seward, and any other questions you have. More info Here.

Wed, February 21st, 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
Thu, February 22nd, 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
Thu, February 22nd, 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

There was very low visibility yesterday, but we saw widespread natural wet avalanche activity on our drive south from Turnagain Pass in the avalanche acres area south of the Sterling Wye. We also saw a small new glide avalanche at about 1,700′ on a southwest aspect of John Mountain in Summit Lake. On Tuesday, February 19 a motorized Level 2 course saw a recent natural slab avalanche on the frontside of Seattle Ridge, north of the common uptrack with a crown at about 1,200′. If you get out today and see any new avalanches send us a photo here!

Fresh glide avalanche at about 1,700′ on a southwest aspect of John Mountain in Summit Lake. Photo 2.20.2024

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

Wind slab and storm slab natural avalanches are possible and human triggered are likely today in the treeline and above elevations due to strong wind and new snow. Wind slab avalanches are the main concern with sustained ridgetop winds yesterday of 30 mph and plenty of new snow, wind slabs will be large and dangerous. Winds today are forecast to be 20 to 30 mph gusting to 50 mph or more so a new round of wind slabs will be forming. Storm slabs are more likely in places like Girdwood, Placer, and Portage Valleys where the mountains received at least 12″ of new snow. These new snow avalanches will be less likely in the sheltered areas of Turnagain Pass that received less than 12″ of snow. If you are seeking out these sheltered areas today during the brief break in storms careful snowpack evaluation will be required. Watch for smooth “pillows” of snow that may feel firm beneath you, dig a hand pit, and ride or jump on a small wind loaded test slope to see how the new snow is bonding to the old snow and crust that formed Monday night.

Persistent Slab Avalanches:  The January facet layer is gaining strength in places like Turnagain Pass. It’s been just a week since the avalanche accident on John Mountain in Summit Lake and there was an avalanche in the Placer area, we believe failed on the facets on February 14 so we know there are places where this layer is still weak, but we think it is unlikely a person would trigger an avalanche on this layer in Turnagain Pass. The only way to assess this problem is to dig a snowpit. Look for weak sugary snow 1-3′ below the surface, which indicates poor structure regardless of test results. Stable test results don’t always mean you won’t trigger an avalanche, but unstable results are clear signs that the weak layer needs more time to strengthen. This is a tricky problem, and you can avoid it entirely by sticking to slopes less than 30 degrees.

Shooting cracks on a fresh wind slab yesterday on Tincan around treeline, a clear sign of unstable snow. 2.20.2024

 

Avalanche Problem 2
  • Wet Slab
    Wet Slab
  • Aspect/Elevation
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
Wet Slab
Wet Slab avalanches are the release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slabs can be very unpredictable and destructive.

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

With a large amount of rain falling to at least 1,500′ recently (1.8″ of water in Girdwood in the last 2 days) natural wet loose and wet slab avalanches will be possible in places that didn’t freeze up last night. The lower to mid elevations of Girdwood haven’t had a hard freeze in over three days, which makes these dangerous avalanches more likely. We recommend avoiding this problem and bad riding conditions entirely and choosing terrain in the treeline elevation band during this stormy weather. The storm arriving today looks to finish cold which will likely make the wet avalanche problem go away in the coming days, stay tuned.

The visibility was limited yesterday, but you can see the wet debris at the bottom of this steep gully in avalanche acres south of the Sterling Wye. Wet debris was widespread in this area. Photo  2.20.2024

Weather
Wed, February 21st, 2024

Yesterday: A large warm storm impacted the region yesterday bringing almost 2″ of water and 18-24″ of snow to the upper elevations of Girdwood and Seward accompanied by strong easterly winds region wide. Turnagain Pass and Summit received closer to 1″ of water which amounted to 8″ of snow at the Center Ridge weather station. It rained to at least 1,500′ although the snow line fluctuated throughout the storm. Temperatures cooled as the precipitation tapered off in the evening.

Today: There is currently a short-lived break between storms. The next front is approaching and luckily this one is cooler. Clouds should build this morning and precipitation could begin as early as noon. Girdwood and Turnagain Pass could see 1-2″ of new snow, Summit 4-6″, and Seward as much as 1′ by this evening. Ridgetop easterly winds calmed into the teens overnight and look to build to 20 to 40 mph gusting to 60 mph or more throughout the day.

Tomorrow: The bulk of the precipitation with this front will arrive overnight and tomorrow. Snow line should remain below 500′ except in Seward where it may reach 800′ overnight before cooling as the storm moves out. Snow totals by the end of Thursday look to be just 4-6″ in Turnagain, 6-18″ in Girdwood, 8-10″ in Summit, and 10-30″ in Seward where precipitation accumulation looks the highest. The higher amounts will be in the upper elevations. Winds are forecast to shift to the south and southwest and calm to the teens by Thursday.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 31 8 0.9 89
Summit Lake (1400′) 33 rain 0.6 39
Alyeska Mid (1700′) 34 2 1.1 79
Bear Valley – Portage (132′) 37 rain 2.64
Grouse Ck (700′) 35 2 1.2 60

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 23 ENE 30 77
Seattle Ridge (2400′) 26 ESE 11 32
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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.