Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Fri, March 5th, 2021 - 7:00AM
Expires
Sat, March 6th, 2021 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger is MODERATE at all elevations. In the higher terrain and in exposed areas in the trees, watch for small newly formed wind slabs due to a bump in easterly winds last night. If found, new wind slabs will be possible trigger, yet expected to be in the 6-8″ deep range. Additionally, triggering an avalanche failing in buried weak layers 1-3’ deep is still possible on slopes 35° and steeper, including those under 1,000. Always remember to give cornices a wide berth and watch your sluff.

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Fri, March 5th, 2021
Alpine
Above 2,500'
Moderate (2)
Avalanche risk
Treeline
1,000'-2,500'
Moderate (2)
Avalanche risk
Below Treeline
Below 1,000'
Moderate (2)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
Moderate (2)
Treeline
1,000'-2,500'
Avalanche risk
Moderate (2)
Below Treeline
Below 1,000'
Avalanche risk
Moderate (2)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Avalanche Problem 1
  • Wind Slabs
    Wind Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    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.

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 hopes for a few inches of new snow in our forecast area today is dwindling fast… As seems to be the theme for the past 5 weeks, it is looking like more blow than snow. The front that was heading our way has stalled just to the west and stretching out along Cook Inlet currently. That said, only a few flurries are expected and maybe an inch in a favored location.

The winds on the other hand are a bit of a game changer. Ridgetop weather stations have been steady in the 15-20mph range from the east since 5pm last night with gusts near 30mph. These speeds are expected to decrease throughout the day. A report from the Magnum/Cornbiscuit area at Turnagain Pass described some ‘active wind loading’ beginning around 4pm yesterday. Although these speeds aren’t super impressive, they should be just enough to drift the 4-8″ of existing light surface snow into wind slabs. Slab thickness is likely to be in the 6-8″ range in general and up to a foot thick in the most windy zones.

Fresh Wind Slabs:  The good news is, new wind slabs should be on the smaller side and easy to identify. They are likely to be in the higher terrain above treeline. Watch for areas with recent wind deposited snow and/or active loading. Smooth rounded pillow like surfaces and stiffer snow over softer snow are tell-tale signs of wind slabs, along with any cracking in the snow around you. These should be on the softer side due to the moderate winds. Slabs may be sitting on a fresh batch of surface hoar from the past several days, or on a thin sun crust on steep south slopes, making them a bit easier to trigger in this case.

 

This table is from the Snow Weather and Avalanche Guidelines and tells us what wind speeds begin to move snow into wind slabs. 


Sluffs:
  Steep slopes that have been protected from the winds and the sun have 2-6” of soft snow on the surface and triggering a loose snow avalanche (sluff) is possible.  Remember sluffs can gain volume and speed in steep terrain and can be dangerous if they knock you off your feet and take you for a ride in a high consequence spot.

Soft surface snow over a thin sun crust on a steep south slope.

Avalanche Problem 2
  • Persistent Slabs
    Persistent Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    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.

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

We continue to track two weak layers of snow (surface hoar and facets) buried in the top three feet of the snowpack. The data continues to show triggering an avalanche in one of these layers remains possible. The layers are present in most areas and at all the elevation bands. The trick is, they are not reactive everywhere. They seem to be more of an issue below 2000′. However, a persistent slab avalanche in upper elevation terrain cannot be ruled out. Triggering a recently formed wind slab or cornice fall may step down to one of these buried weak layers. Additionally, there may be older hard wind slabs sitting on top of the weak layers, allowing a person to get well out onto the slope before an avalanche initiates or an avalanche may occur after other machines or skiers have already ridden the slope. Watch for signs of instability, follow safe travel protocol and evaluate terrain consequences.

Weather
Fri, March 5th, 2021
Yesterday:  It was a gorgeous bluebird day over the region yesterday. Ridgetop winds started light from the east then steadily climbed through the afternoon and have been blowing overnight in the 15-20mph range with gusts in the 30's. Temperatures were in the 20'sF at the lower elevations and teens at the higher. Today:  Partly cloudy skies, a chance for a few flurries and moderate east ridgetop winds is all this weather front looks to have in store today. The ridgetop winds are forecast to average 15-20mph from the east with stronger gusts before letting up this afternoon. Temperatures will be warmer today, climbing to the mid 30'sF at sea level and the low 20'sF in the higher terrain. Tomorrow:  Clouds are expected to linger to some degree tomorrow before skies clear up on Sunday. Ridgetop winds will swing back around to the NW and models are showing them pick up into the 15-20mph range along the ridgelines Saturday. Stronger NW outflow winds are expected down near Seward. Temperatures will remain mild, near 30F at sea level and 20F in the Alpine. PRECIPITATION 24-hour data (6am - 6am)
Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 24 0 0 112
Summit Lake (1400') 15 0 0 46
Alyeska Mid (1700') 22 0 0 116
RIDGETOP 24-hour data (6am - 6am)
Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 16 NE 11* 31
Seattle Ridge (2400') 20 SE 9 20
*Easterly winds have been averaging 15-20mph since 5pm.
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Riding Areas
Updated Tue, June 01st, 2021

Status of riding areas across the Chugach NF is managed by the Glacier and Seward Ranger Districts, not avalanche center staff. Riding area information is posted as a public service to our users and updated based on snow depth and snow density to prevent resource damage at trailhead locations. Riding area questions contact: mailroom_r10_chugach@fs.fed.us

Area Status Weather & Riding Conditions
Glacier District
Johnson Pass
Closed
Placer River
Closed
It is packrafting and jetboat season!
Skookum Drainage
Closed
The Skookum Valley is closed to snowmachines. This closure occurs annually on April 1 as per the CNF Forest Plan.
Turnagain Pass
Closed
Closed as of June 1. 188 day season, that\'s a wrap!
Twentymile
Closed
It is packrafting and jetboat season!
Seward District
Carter Lake
Closed
Closes May 1.
Lost Lake Trail
Closed
Closes May 1.
Primrose Trail
Closed
Closes May 1.
Resurrection Pass Trail
Closed
Closed for the 2020/21 winter season. Will be open for moto use in the 21/22\\\' winter season as per the CNF Forest plan.
Snug Harbor
Closed
Closes May 16th.
South Fork Snow River Corridor
Closed
Closes May 1.
Summit Lake
Closed
Closes May 1.

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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.