Turnagain Pass RSS

Archives
ARCHIVED - Forecasts expire after 24 hours.
Issued
Wed, December 20th, 2023 - 7:00AM
Expires
Thu, December 21st, 2023 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger is MODERATE at all elevations. Triggering an avalanche in the new 6-12″ of snow from last night is possible. Watch for shallow storm slabs and wind slabs that could be 1-2′ deep along the ridgelines. Dry loose snow sluffs will also be possible. The higher the new snow amounts are, the better chance we’ll have at triggering an avalanche. Additionally, there is rare chance a person could trigger a large avalanche on weak snow forming near a crust 3-5′ below the snow surface.

GIRDWOOD/PLACER VALLEYS:  If new snow amounts are more than 12″ these new snow avalanches issues will be larger and the avalanche danger may be closer to CONSIDERABLE.

SUMMIT/LOST LAKE/SEWARD:  Snowfall in these areas overnight will make for similar new snow avalanche concerns for areas on the Kenai.

Special Announcements

Looking for that perfect stoking stuffer? Consider singing someone up to be a Member in December! The Friends of the Chugach Avalanche Center, our non-profit arm, needs your help to keep us operational. Everyone who donates during the month of December will be entered to win some awesome prizes given out at Andrew’s Girdwood Brewery Forecaster Chat on January 19.

Wed, December 20th, 2023
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
Avalanche risk
Thu, December 21st, 2023
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
Avalanche risk
Thu, December 21st, 2023
Alpine
Above 2,500'
2 - Moderate
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

The last known avalanche activity was associated with the warm storm Saturday night that brought 8-12″ of new snow across the region. Widespread storm snow avalanches were seen once the skies cleared on Monday from Girdwood, Turnagain Pass, to Seward.

Avalanche Problem 1
  • Storm Slabs
    Storm Slabs
  • Aspect/Elevation
  • 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.

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 light snow fell during the daylight hours yesterday (5 hours and 34 minutes worth of daylight), snowfall rates picked up overnight. Highest amounts were seen in the upper elevations of Girdwood Valley, Portage/Placer, and Seward. Ridgetop winds were easterly with the snowfall, 10-20mph with gusts near 40, but the good news is, those winds died off overnight as most of the snow fell. That said, today will be day to suss out how much new snow is in the area you are traveling and did it get hit by any winds. The primary avalanche issues will be related to those new snow amounts. Here are some snowfall totals-

Snowfall totals from yesterday (estimated at mid elevations):
Girdwood Valley: 8-12″
Turnagain Pass:  4-6″
Summit Lake:  4-6″
Lost Lake/Seward:  8-12″

New Snow Avalanches:  These could be storm slabs, wind slabs, and dry loose snow sluffs. All of them could be found today, especially in areas that saw 10″ or more of new snow such as in Girdwood and Placer Valleys. Storm slabs will be the depth of the new snow (ish) and found in areas that did not see any wind effect. Wind slabs could be up to 2′ deep along ridgelines where any wind did occur. As always, keep a close eye out for Red Flags – Recent Avalanche, Cracking in the snow around you, and whumpfing sounds/collapsing of the snowpack. The good news is, all these new snow avalanche types should be on the smaller side and easy to identify if we are paying attention.

In areas with only 4-6″ of new snow, avalanches in the new snow will be less of a concern except for wind slabs that may have formed in the higher terrain.

 

Conditions yesterday on Tincan at Turnagain Pass. Light snowfall, temps in 20’sF, and low light/short days. Photo from Hamer/ Asher 12/19/23.

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

Last night’s snow was not quite enough to put much added weight on the snowpack and the buried weak layer we keep talking about. This is the faceted snow that is forming near the Thanksgiving Crust, now buried around 3-5′ deep. We’ve been tracking this layer for almost a month and so far the layer has been unreactive. There have been two known avalanches failing on this layer since the crust was buried, around a week ago.

This issue is notoriously difficult to deal with. The short story is we don’t want anyone to be caught off guard; even though the snowpack can seem bomber under the new snow, it may not be. The likelihood of triggering an avalanche on this layer is low, but if you were to trigger something it could be very large. All slopes above 1000′ should be considered suspect, since we’ve seen the same suspicious structure in virtually every snowpit that has been dug over the past two weeks.

Snowpack at the lower elevations of Turnagain Pass. Snow pit tests here showed the weak snow was sandwiched in between the Thanksgiving Crust but was not failing in tests (meaning a strong pack unlikely for a person to trigger a big avalanche here). 12/17/23.

Weather
Wed, December 20th, 2023

Yesterday:  Cloudy skies and light snowfall was seen over the region yesterday. Precipitation picked up overnight and between 4-12″ of snow (to sea level) was reported. Highest amounts in Girdwood, Portage, and Seward. Ridgetop winds were easterly, 10-20mph with gusts near 40mph, before quieting overnight. Temperatures were in the 20’sF at the mid elevations and 30-14F at sea level.

Today:  Clearing skies with valley fog is forecast as the storm moves out. Ridgetop winds are calm this morning and expected to be light from the west later today (5-10mph). Temperatures will be dropping into the teens through the day. No precipitation is expected.

Tomorrow:  Weather models are showing a break in weather for tomorrow, Thursday, into Friday. Partly cloudy to clear skies are shaping up for Thursday along with cold temperatures (5-15F). Ridgetop winds should remain light from the west and north. A stronger storm with warmer temperatures arrives on Saturday into Christmas Eve.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 26 5 0.4 76
Summit Lake (1400′) 24 5 0.4 42
Alyeska Mid (1700′) 27 6 0.62 73
Bear Valley – Portage (132′) 31 5-7″ 1 (estimated)
Grouse Ck – Seward (700′) 29 9 0.6 48

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 19 NE 18 40
Seattle Ridge (2400′) 23 SE 8 15
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
Riding Areas

The riding areas page has moved. Please click here & update your bookmarks.


Subscribe to Turnagain Pass
Avalanche Forecast by Email

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.