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ARCHIVED - Forecasts expire after 24 hours.
Issued
Mon, November 27th, 2023 - 7:00AM
Expires
Tue, November 28th, 2023 - 7:00AM
Forecaster
John Sykes
Avalanche risk The Bottom Line

Today’s avalanche danger is CONSIDERABLE above 2500′. Strong winds will form wind slabs that could cause natural or human triggered avalanches 1-2′ deep. We have little information about the alpine snowpack over the past week and recommend a cautious approach if you venture into higher elevation terrain. Below 2500′ the avalanche danger is MODERATE. Wet loose and glide avalanches are possible due to the warm temperatures and rain.

Roof Avalanches: Until the temperatures drop below freezing we continue to be concerned about the potential for roof avalanches.

Special Announcements

Hatcher Pass: The SW flow direction of our current storm system will favor the Talkeetna’s today. Up to a foot of new snow could fall at Hatcher Pass, which will rapidly increase avalanche danger. Check out hpavlanche.org for more information!

New weekend outlook products:  Starting Friday, Dec. 1, we will begin issuing Weekend Avalanche Outlooks for Chugach State Park, the Summit Lake/Central Kenai zone, and the Seward/Southern Kenai zone. These Outlook products will be published Friday evenings and will provide avalanche information for these three new areas for us.

Mon, November 27th, 2023
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
Avalanche risk
Tue, November 28th, 2023
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
Avalanche risk
Tue, November 28th, 2023
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
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

No recent avalanches were reported yesterday. Widespread wet loose and glide avalanches have been observed since the onset of this wet weather pattern last Wednesday, especially in the Girdwood and Portage areas where the precipitation has been heaviest.

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

Since the start of this series of wet and warm storm systems last Wednesday Turnagain Pass has received a total of 1.4″ of water, with Girdwood receiving 2.5″, and Portage 10.7″. Unfortunately that precipitation fell as mostly rain below 2000 – 2500′. However, in the alpine that means anywhere from 1.5′ of new snow in Turnagain to 11′ of new snow in Portage within the past week! Today rain line will gradually drop to sea level throughout the day with snow showers possible through the afternoon and the potential for clearing skies in the evening.

Strong SW winds will continue to impact the forecast area today with averages of 20-35 mph and gusts to 50 mph. Above 2000 – 2500′ where the recent precipitation fell as snow, we will see fresh wind slabs 1-2+’ deep forming along exposed ridgelines and convex terrain features. Using small test slopes can be an effective method to check how reactive wind slabs are before committing to more consequential terrain. If you venture into the alpine today be aware that we have very little information from the past week, and we recommend careful evaluation of how the new storm snow is bonding with the existing snowpack.

Recent storms brought rain to low elevations, but new snow above 2500′. We have no information about how well the snowpack is adjusting to the new load at upper elevations. Photo 11.25.23

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

The colder temperatures and clearing skies this evening should help lock up the wet snowpack at lower elevations and decrease the likelihood of wet loose avalanches. However, it will probably take some time for the wet snow on the surface to gain strength and wet loose avalanche will still be possible on steep terrain features today. These can become destructive in larger terrain, so it is important to be aware of your surroundings if you see signs of wet loose avalanches. The typical signs are roller balls or pin wheels that are releasing naturally or triggered by a skier.

Melt water runnels and a naturally released pinwheel on a steep rollover near treeline on Tincan. 11.25.23

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

Glide cracks have been opening up across the forecast area and many glide avalanches have released in the past few days. These can produce large and destructive avalanches, so we recommend avoiding spending time underneath glide cracks. With the limited visibility over the past few days it can be difficult to see whether there is a glide crack above you, so we recommend sticking to familiar routes and minimizing the amount of steep terrain overhead.

Weather
Mon, November 27th, 2023

Yesterday: Another day of warm temperatures across the forecast area, averaging in the high 30s F at sea level, around 32 F around 1500′, and 25 F at ridgetop elevations around 3500′. Girdwood and Portage again saw much more precipitation with 0.8″ of water and 2.0″ of water respectively. Turnagain and Summit Lake only received 0.2″ of water yesterday. Rain line was approximately 2000′. Wind speeds averaging 10-20 mph with gusts to 35 mph yesteray morning, then calmed down in the afternoon with averages around 10 mph and gusts of 15-20 mph. Overnight winds picked back up again with averages of 20-30 mph and gusts to 50 mph from 10pm onwards.

Today: Temperatures are expected to drop today as a colder air mass moves into our area. Rain line should move down to sea level as we see a roughly 10 degree drop in temperatures throughout the day today. Precipitation should also taper off this morning with snow showers expected for most of the day amounting to 0.1-0.3″ of water expected during the daylight hours today. We should see moderate to strong SW winds today with averages of 20-35 mph and gusts up to 50 mph throughout the day. Winds speeds will shift to the south and decrease slightly this evening as another storm system enters the area. Cloud cover should decrease throughout the day with a brief period of clearing skies this evening.

Tomorrow: Another storm system should move into the area Tuesday morning with temperatures increasing again, but rain line is expected to remain below 1000′ for the duration of this next storm system. We expect another 0.5-1.0″ of water from Tuesday morning through Wednesday morning in our forecast area. SW winds will increase on Tuesday afternoon and evening averaging 30-45 mph and gusting 60+mph.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 32 0 0.2 28
Summit Lake (1400′) 32 1 0.2 16
Alyeska Mid (1700′) 33 0 0.8 21
Bear Valley – Portage (132′) 38 0 2.0

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 26 ENE 16 51
Seattle Ridge (2400′) 29 SE 8 26
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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.