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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Graham Predeger  
Tuesday, March 1st 2016
Created: Mar 1st 6:22 am
3 Considerable Alpine / Above 2,500' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
3 Considerable Treeline / 1,000'-2,500' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
2 Moderate Below Treeline / Below 1,000' Travel Advice: Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
 Show the Complete North American Avalanche Danger Scale
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.


Primary Concern

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.


Secondary Concern

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.


Mountain Weather

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  .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 

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).

Winter snowmachine use open/closed status and riding conditions updates

Riding status is not associated with avalanche danger. An area will be open to motorized use in accordance to the Forest Management Plan when snow coverage is adequate to protect underlying vegetation. Backcountry hazards including avalanche hazard are always present regardless of the open status of motorized use areas.

(Updated: May 16, 2017 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: Closed
Placer River: Closed
Skookum Drainage: Closed
Turnagain Pass: ClosedThanks all for a safe and fun season on the Chugach NF! Stay tuned for the 2017/18 season. #playsafe #snowtosealevel
Twentymile: Closed
Seward District
Carter Lake: Closed
Lost Lake Trail: Closed
Primrose Trail: Closed
Resurrection Pass Trail: ClosedResurrection Pass trail will be open to snowmachine use during the 2017/18 winter season.
Snug Harbor: Closed
South Fork Snow River Corridor: Closed
Summit Lake: Closed

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The information in this advisory is from the U.S. Forest Service, which is solely responsible for its content. This advisory describes general avalanche conditions and local variations always occur. This advisory provided by the Chugach National Forest, in partnership with Friends of the Chugach National Forest Avalanche Information Center.


USFS SNOW AND AVALANCHE HOTLINE (907) 754-2369
If you have comments or questions regarding CNFAIC operations or winter recreation management, please email staff@chugachavalanche.org
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