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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Tue, March 1st, 2016 - 7:00AM
Expires
Wed, March 2nd, 2016 - 7:00AM
Forecaster
Graham Predeger
The Bottom Line

Avalanche Danger in the Alpine and treeline elevations (above 1,000′) is CONSIDERABLE today given a multitude of different avalanche problems currently present.   As this 9-day storm begins to wrap up today we have very little data from the alpine.   What data we do have, points toward a snowpack with some potential mid-storm weaknesses that needs time to adapt to an enormous load of snow and water weight (11 €+ water over 9 days).   Very cautious route finding and conservative decision-making will be essential today if venturing into the mountains.  The sun is expected to make an appearance today and its worth noting that direct sun and warming temperatures will compound these avalanche problems listed below.

The danger is  MODERATE  below 1,000′ where debris from an avalanche above could run in steep terrain.

Elevated caution and a conservative mindset is recommended in the Summit Lake area where a variety of avalanche concerns also exist. See Saturday’s  Summit Lake Summary  and click  HERE  for recent observations.

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Tue, March 1st, 2016
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
  • Storm Slabs
    Storm Slabs
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.
More info at Avalanche.org

With just a few short breaks in weather over the last 9 days, we appear to be on the verge of a pattern change as it looks like we’ll be under at least a couple of days of high pressure starting this afternoon.  Storm snow issues listed below are of concern today and may prove more reactive if we get a spike in ambient temperatures, or a period of unobstructed sunshine.

Storm slabs:  Yesterday we found reactive storm slabs at 2500’ in our snow pit that consistently failed and propagated about 2 feet below the surface.  Granted, this is only one data point, but it happens to be on arguably the most heavily traveled piece of terrain in the Turnagain zone (Seattle ridge uptrack).  This may have been the same weak layer responsible for a Sunday afternoon natural storm slab on Tincan.  More data will help us understand if this weakness is widespread, but for today, keeping slope angles mellow and picking very conservative travel routes will be key.

Pit results yesterday identified a concerning mid-storm crust at 2500′ on Seattle ridge that proved reactive.  See video here.

Wind slabs:  There is ample snow available in the alpine for transport.  Winds have been primarily from the E and NE over the last several days loading any slope with a westerly tilt.  Last night, winds kicked back up into the 40’s, gusting to 70mph on Sunburst.  As with their cornice brethren, wind slabs have the potential to be large and dangerous today.  Avoid steep, wind loaded slopes and recognize that any direct sun today could act to weaken these wind slabs.

Cornices: These continue to grow large and unruly with the addition of more wind and snow.  Give cornices a wide berth if travelling on or below a corniced ridge.  Any significant cornice fall today is likely to trigger an avalanche on the slope below.

Avalanche Problem 2
  • 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

The wild card…. Glide cracks have continued to release during this storm cycle, still with no real discernable pattern.  Many cracks continue to litter the slopes above well-travelled terrain on both the motorized and non-motorized side of the highway.  Simply avoid exposure time spent below existing cracks to minimize your risk.  The photo below is a good reminder that if a skier or snowmachiner were to tangle with one of these full-depth glide avalanches, odds of survival are slim to none.

Snowmachine for scale next to the toe of a glide avalanche.  This released Thursday night/ Friday morning on the East face of Seattle ridge depositing 15-20′ of debris on a well-traveled snowmachine route.

Weather
Tue, March 1st, 2016

Temperatures at 1,000′ were slightly cooler yesterday (32F) than they have been for several days.   This promoted a discernable rain/ snow line at about 500′ with a few short bursts of snow at sea level before turning to all rain.   New snow accumulation added up to 4-6 € at 1,000′.   Winds were in the teens and gusting to the 30’s mph at ridgetop locations as clouds funneled in and out of the Pass.

A pattern change is underway today as stormy weather gives way to clearing skies, calming winds and cooler temperatures overnight tonight.   Today winds are expected to start out in the 15-30mph range from the East, dropping off to single digits by this afternoon.   Temperatures at 1,000′ will be in the low to mid-30’s F before cooling off overnight and we may see 1-2 € of snow squeezed out this morning before skies break apart.

High pressure will dominate through Thursday before our next chance of snow arrives prior to the weekend.

A quick snapshot of SWE data at the Turnagain Pass SNOTEL thru February.  Red is current water year.  Green is the long-term average and blue is the year we’d all like to forget (last year).

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 30   4-6″  .6 146  
Summit Lake (1400′) 32   0   .1   41  
Alyeska Mid (1700′)  32  2 .2   106  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 21   ENE   26   70  
Seattle Ridge (2400′) 24    n/a n/a   n/a  
Observations
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Riding Areas
Updated Wed, December 11th, 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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