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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Fri, December 8th, 2017 - 7:00AM
Expires
Sat, December 9th, 2017 - 7:00AM
Forecaster
Heather Thamm
The Bottom Line

The avalanche danger is  CONSIDERABLE where triggering an avalanche 2-4+ feet thick will be likely above 1500′. Remote triggered avalanches are also likely and could run further than expected. Small slopes and large slopes are all suspect and it will be very important to avoid slopes steeper than 35 degrees, terrain traps and runout zones.  Triggering a wet avalanche is also possible today below 2000′.  Cautious route-finding, conservative decision-making are essential.    

Below 1000′ the avalanche danger is MODERATE where a wet avalanche from above could run into this elevation band.  

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Fri, December 8th, 2017
Alpine
Above 2,500'
Considerable (3)
Avalanche risk
Treeline
1,000'-2,500'
Considerable (3)
Avalanche risk
Below Treeline
Below 1,000'
Moderate (2)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
Considerable (3)
Treeline
1,000'-2,500'
Avalanche risk
Considerable (3)
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
  • Persistent Slabs
    Persistent Slabs
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.
More info at Avalanche.org

Was yesterday’s rain and snow enough to tip the balance for a widespread natural cycle? Or is our scary snowpack still lingering in place? 

Yesterday’s potent storm brought heavy rain to 2000’ and strong Easterly winds averaging in the 30’s with gusts in the 70’s. Precipitation amounts varied across our region favoring Girdwood with 1.5” of rain and Turnagain Pass seeing around .5” of rain. New snow totals in the upper elevations could range from 1-2+ feet. Visibility yesterday was poor and its unknown how much natural avalanche activity may have occurred. The Northern end of Turnagain Pass is likely to have higher snow totals similar to Girdwood. 

Incremental loading from multiple storms over the last two weeks in the Kenai Mountains have buried a reactive layer of weak faceted snow near the ground. Numerous human triggered avalanches have occurred almost daily since November 28th and today will be similar. The only difference is the slab is thicker and the consequences of getting caught are greater. Triggering an avalanche could propagate an entire slope releasing on the ground and running the entire slide path. Remotely triggering an avalanche from far away is also likely today, as seen two days ago at Tincan. See photos below. This is not an avalanche problem that can be out smarted or easily managed. Avoiding all runout zones and avalanche terrain steeper than 35 degrees is essential. Obvious signs of instability have been present all week including recent avalanches, collapsing ’whumpfing’, temperatures above freezing, heavy precipitation, and strong winds. Remember these red flags are evidence the snowpack is unstable. Today there will be a break between storms and if the visiblity improves be careful to not get tempted into avalanche terrain including small features with terrain traps. 

The avalanche on the left side of this photo was triggered remotely from 100’s of feet away by a party that re-grouped below Common bowl, Tincan SW aspect on Wed. Dec.6. A second avalanche also released on the opposite side of the ridge, a Northern aspect, at the same time. See photo below. This is a really scary snowpack set-up: A dense slab sitting on top of a persistent weak layer of facets connected by a slick bed-surface. Expect this problem to persist through the weekend.     

 

Remote triggered avalanche on a Northen aspect of Tincan, opposite side of the ridge from the avalanche in the above photo. The starting zone of these two avalanches is around 2500′.  

Avalanche Problem 2
  • Wind Slabs
    Wind Slabs
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.
More info at Avalanche.org

Strong Easterly winds have loaded leeward aspects, cross loaded many gullies and loaded corniced ridges. Human triggered wind slab avalanches or cornice falls are likely, but what is more of a concern is the potential for one of these to trigger a much larger and dangerous persistent slab avalanche as discussed above.  AGAIN today is not the day to be pushing into avalanche terrain! 

Additional Concern
  • Wet Loose
    Wet Loose
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.
More info at Avalanche.org

Rain on snow has occurred in the mid elevations (1000′ – 2000′) and wet loose avalanches are possible today. Above freezing temperatures may keep this avalanche problem lingering throughout the day and is an additional reason to avoid being on or underneath steep slopes. Although not much snow exists below 1000’ a wet avalanche from above could run into this zone. 

A view of Magnum’s West face from yesterday around 3:30pm. Several small slabs released below 2000′. This area is on the Southern end of Turnagain Pass and has recieved lower rain and snow amounts. 

Weather
Fri, December 8th, 2017

Yesterday a warm and potent storm impacted our region bringing varying amounts of rain and snow to our forecast zone. Strong Easterly winds averaged in the 30’s with gusts in the 70’s. Girdwood was favored receiving 1.55 € of rain at Alyeska mid-way weather station, an estimated 15-24 € in the alpine. Center Ridge Snotel in Turnagain Pass picked up 0.5 € of rain, an estimated 6-12 € of snow in the alpine.   Rain/snow line likely fluctuated between 1500′ and 2000′. Temperatures remained above freezing yesterday and overnight in the mid and lower elevations.  

A break between storms is expected today into Saturday. Light precipitation in the form of rain below 2000′ may fall through out the day with a possibility of patches of clear skies. Temperatures should remain warm in the mid 30F’s and may keep freezing level as high as 2000′. Light Easterly winds should be in the 5-15mph range.    

Tomorrow East winds are expected increase to Moderate in the morning as another front moves into our region. The exact timing of this storm and precipitation amounts are uncertain, but temperatures are expected remain above freezing bringing more rain to the mid and lower elevations.   Our current South to North jet stream has another warm, wet and windy storm on tap for our region Sunday evening into Monday.  

*Center Ridge SNOTEL is reporting erroneous temperature data. See  Turnagain Pass DOT weather station  for accurate temperature at 1000′.

**Seattle Ridge anemometer has been covered with rime and started working yesterday. The reported winds don’t reflect the overall impact of winds to this region.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) *36   0   0.5 27  
Summit Lake (1400′) 34   0   0.4   11  
Alyeska Mid (1700′) 34 5   1.55 19  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 27   ENE   25   74  
Seattle Ridge (2400′) 30   **ESE   **4     **32  
Observations
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Riding Areas
Updated Mon, December 02nd, 2019

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
Closed.
Placer River
Closed
Closed.
Skookum Drainage
Closed
Closed.
Turnagain Pass
Closed
Closed.
Twentymile
Closed
Closed.
Seward District
Carter Lake
Closed
Closed.
Lost Lake Trail
Closed
Closed.
Primrose Trail
Closed
Closed.
Resurrection Pass Trail
Closed
Closed. Will be open for the 2019/20 season pending adequate snow cover.
Snug Harbor
Closed
Closed.
South Fork Snow River Corridor
Closed
Closed.
Summit Lake
Closed
Closed.

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