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Avalanche Advisory

Turnagain Area Avalanche Advisory
Friday, April 12th 2019 7:00 am by Heather Thamm
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
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The Bottom Line

The avalanche danger is CONSIDERABLE today above 2500' where strong winds and new snow have created touchy slabs 1-3' thick. In the Treeline zone (1000'-2500') the avalanche danger is MODERATE where the snowpack transitions from wet snow to dry snow. Within this zone triggering a wet loose avalanche or storm slab is possible. Any sign of sun or thin cloud cover today could quickly heat up this new snow and increase the potential for wet loose avalanches. Evaluate terrain and snow as you travel and keep your slopes angles below 35 degrees until this new snow has time re-freeze. Additionally - identify cornices and glide cracks and avoid travel below these unpredictable features.

PORTAGE VALLEY: Very little snow exists below 1000', but summer trails with large steep slopes directly overhead, such as the Byron Glacier Trail, provide easy access for accidentally being in a dangerous place. Cornice fall or an avalanche from above has the potential to run to valley bottom. Travel in these areas is not recommended.


 Show the Complete North American Avalanche Danger Scale
3 Considerable Alpine / Above 2,500' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
2 Moderate Treeline / 1,000'-2,500' Travel Advice: Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
0 NO RATING Below Treeline / Below 1,000'
Avalanche Problem 1

Wind Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
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Size

A powerful storm yesterday dumped 1-3’ of new snow in the upper elevations, rain below 1000’, and blasted our region with very strong wind. Easterly ridgetop winds averaged in the 40s with gusts reaching 80-90 mph. A variety of storm related avalanche problem exist today and will require careful snowpack evaluation and cautious route finding and a flexible plan if the sun comes out. Snow totals could range from 1-2’ thick in Girdwood and Turnagain Pass, and 3’ in the upper elevations of Portage Valley. Rain/snow line fluctuated between 2000’ and 1000’ yesterday which means you will encounter wet heavy snow transitioning to drier snow with elevation. Keep the following in mind today:

WIND SLABS: In the alpine where strong winds have drifted new snow, slabs could be up to 2’ thick in heart of Turnagain Pass. Look for wind loaded features and avoid slopes steeper than 35 degrees. Larger and more connected slopes will have higher consequences if you trigger a slab. Look for obvious clues like shooting cracks and recent avalanches. Any additional blowing snow or radiation from the sun will make these slabs more touchy today.

STORM SLABS: Areas less affected by strong winds that are harboring dry snow - triggering a storm slab is possible. As you travel pay attention to where wet snow transitions to drier snow and how thick the slab becomes with elevation. Avoid steep features and terrain traps that could get a skier or rider in trouble.

CORNICES: Expect cornices to be large and unstable. Give these features lots of space - they often break further onto a ridge than expected. Natural cornice fall could trigger a slab below. 

Rain/snow line dropped to 1000' yesterday afternoon at Turnagain Pass with 1cm of wet slushy snow accumulation. The upper elevations likely have 1-2' of new snow.

 


Avalanche Problem 2

Wet Loose

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
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Small

Size

Below 2000’ where wet snow and rain fell yesterday, triggering a wet avalanche will be possible on steep terrain features. The more saturated the snow, the more potential for a small point release to entrain snow and build momentum. Daily warming and any sign of sun or thin cloud cover could increase the potential for wet loose avalanches. If you find your skis or machine sinking into wet saturated snow avoid slopes steeper than 35 degrees. Pay close attention to how the snow changes throughout the day and with elevation, and be prepared to avoid all South facing slopes later in the day if you feel heat from the sun. This includes all South facing slopes and all elevations.

**Tomorrow looks like our first sunny day following the storm with very little wind. Be aware that warming from the sun will elevate the avalanche danger and potential for triggering both wet loose and storm slabs in the alpine.

Rain and wet snow was falling along Turnagain Pass road level yesterday. Expect the snow surfaces at this elevation to be wet and punchy today. Note how quickly the snow is disappearing! There is little to no snow below 1000'.


Additional Concern

Glide Avalanches

Rain and new snow has added weight to the snowpack and a glide avalanche today would not be suprising. This is the entire snowpack gliding downhill and spontaneously releasing. Our last known glide avalanche was on Sunday near the Hope Wye. Cracks are present in a lot of popular terrain and require a keen eye - to locate and avoid travel below them. They can release at anytime, are completely unpredictable and can be very destructive.


Mountain Weather

Yesterday: A powerful storm yesterday brought a mix of rain, snow and strong wind. Heavy rain fell below 1000’ across the region and heavy snow to the alpine. Precipitation totals ranged from 5-10" of wet snow (0.76"-1.0" SWE) for Alyeska Midway and Turnagain Pass SNOTEL, and 2" of rain for Bear Valley in Portage. Easterly winds averaged in the 40-50s mph with gusts to 80-90mph during the middle of the day. Temperatures at sea level were in the low-40Fs, temps at 1000’ were mid-30Fs and upper elevations were mid-20Fs. Rain/snow line fluctuated between 2000' and 1000'. Overnight Easterly winds diminished to 10-20s mph.

Today: Expect overcast skies and a mix of rain showers below 1500' and snow showers above, with 2-3" (0.2" SWE) of new snow possible. Areas further from the coast may experience broken skies later in the afternoon. Easterly ridgetop winds are expected to be 5-25mph, with gusty winds near Turnagain Arm in the afternoon. Temperatures at sea level will be in the mid-40Fs, temps in the mid elevations upper-30Fs, temps along ridge tops may reach the upper-20Fs.

Tomorrow: Partly cloudy skies are expected as high pressure moves into Southcentral AK. Winds are expected to be light and variable. Temperatures during the day will reach the 40-50Fs at sea level, 40Fs at 1000' and low to mid 30Fs in the upper elevations.

*Seattle Ridge weather station was under-reporting wind data yesterday and stopped recorded at 9pm last night. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 33 10  70 
Summit Lake (1400') 36  rain  0.1  18 
Alyeska Mid (1700') 33  0.76  59 

 

RIDGETOP 24-hour data (6am - 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 24  ENE  36  90 
Seattle Ridge(2400') 29  *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 06, 2019 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: ClosedClosed as of 4.3.19
Placer River: ClosedClosed as of 3.20.19 due to lack of snow.
Skookum Drainage: ClosedPlacer access closed as of 3.20.19 due to lack of snow.
Turnagain Pass: ClosedClosed as of 5/6. Thanks for a great season all, see you next winter!
Twentymile: ClosedClosed as of 3.20.19 due to lack of snow.
Seward District
Carter Lake: Closed
Lost Lake Trail: ClosedClosed as of 3.22.19 due to lack of snow
Primrose Trail: ClosedClosed as of 4.3.19 due to lack of snow
Resurrection Pass Trail: ClosedClosed for the 2018/19 season. Next season will be open to motorized use.
Snug Harbor: ClosedClose as of 5.1.2019
South Fork Snow River Corridor: ClosedClosed as of 3.20.19 due to lack of snow.
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
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