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Avalanche Advisory

Turnagain Area Avalanche Advisory
Thursday, January 24th 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 HIGH above 1500’ due to strong winds and heavy snow this morning. In Girdwood and Portage Valley storm slabs 2-3+’ could release naturally. In Turnagain Pass where less snow has fallen triggering a storm slab up to 1.5’ deep is likely today on slopes greater than 30 degrees. Active wind loading, heavy precipitation and natural avalanche activity are redflag warnings to avoid avalanche terrain. The avalanche danger is CONSIDERABLE below 1500’ where wet loose snow avalanches are possible.

GIRDWOOD: Warming temperatures and rain on old snow = ROOF AVALANCHES. Pay attention to children and pets and where you park your car. 

PORTAGE and PLACER VALLEY:  Heavier rain and snowfall rates have occurred and large avalanches above treeline may send debris to sea level and over summer hiking trails such as Byron Glacier Trail.

SUMMIT LAKE / JOHNSON PASS:  A poor snowpack structure exists in this area, which is very different than Turnagain Pass. New snow/rain and wind may overload weak layers in the snowpack and triggering a larger avalanche is possible. Look for signs of instability and pay attention to changing conditions. 


 Show the Complete North American Avalanche Danger Scale
4 High Alpine / Above 2,500' Travel Advice: Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
4 High Treeline / 1,000'-2,500' Travel Advice: Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
3 Considerable Below Treeline / Below 1,000' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
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Avalanche Problem 1

Storm Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Over the last two days periods of heavy snow and strong winds have created storm slabs in the mid and upper elevations of our forecast zone. The size of these slabs depends on precipitation totals and proximity to coastal areas. Portage Valley and Girdwood have received the highest amounts of precipitation and storm slabs could range from 2-3+’ in these zones. In Turnagain Pass where less snow has fallen storm slabs are expected to range from 8-16” thick. Strong Easterly ridgetop winds have been loading leeward features including a gust to 98 mph at Sunburst Wx station at 6am. Strong Easterly winds are expected to decrease to Moderate and precipitation is also expected to back off. The avalanche danger in Turnagain may decrease to CONSIDERABLE as winds decrease. If you head to an area that received less snowfall please keep in mind that triggering slab today could still be large enough to bury or kill a person. This new snow has fallen on a widespread weak layer of surface hoar  that is sitting on a hard bed surface in many places. Signs of avalanche activity, shooting cracks and collapsing are expected today and will be reminders to avoid avalanche terrain. Be aware -  another storm will impact our region overnight with up to another 1.0” of snow water equivalent (~12” of snow) expected for Turnagian and higher amounts in Girdwood and Portage.

Shooting cracks and small skier triggered storms were observed yesterday on Tincan. 

 

 

A crust bed-surface exists to 2500' and buried surface hoar to ridgetops is also sitting under all of this new snow. This is a bad set-up for new snow to be falling on.  


Avalanche Problem 2

Wet Loose

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Below 2000’ where rain and wet snow have been falling the last two days natural wet loose avalanche are possible today. This avalanche hazard is most concerning in Portage Valley where a natural avalanches from above could run to valley bottoms in steep channeled terrain. Avoiding areas like Byron Glacier trail is recommended.


Additional Concern

Persistent Slabs

South of Turnagain - Johnson Pass/Summit Lake zone: poor snowpack structure exists in these areas.  Multiple mid-pack weak layers of facets and buried surface hoar have been found as well as a facet/crust combination in the bottom of the snowpack. Strong winds, rising temperatures and a few inches of snow over the last two days has added stress to older layers in this zone. The possibility of triggering a slab deeper in the snowpack is the primary concern in this area and a person’s weight may be enough to tip the balance. Look for signs of instability and snow and terrain carefully. 


Mountain Weather

Yesterday: Above freezing temperatures caused precipitation to fall as rain below 1000’. A mix of rain and snow was observed below 1500’ in Turnagian Pass. Girdwood and Portage received the highest precipitation totals with Girdwood at 1.16” SWE and Portage at 2.37” SWE in 24 hours. Turnagain Pass DOT lot recorded 0.6” slightly higher than the Turnagain Pass Snotel at 0.4” SWE. Strong Easterly ridgetop winds in the yesterday morning decreased to Moderate for most of the daylight hours. Overnight Easterly ridgetop winds increased to strong averaging 30-60mph’s with a few gusts in the 90mph’s. Temperatures at sea level reached 40F’s overnight. Rain/snow line may have reached 2000’.

Today: Expect temperatures to remain around 40F at sea level and mid 30F’s at 1000’. Rain/snow line may reach 2500’. Strong winds are expected to decrease this morning to Moderate for most of the day. Tonight another storm is lined up to impact our region. Expect another round of warm temps, heavy rain and strong winds overnight.

Tomorrow: Another low-pressure system will move through our region with heavy rain expected through the morning at lower elevations. Rain/snowline is expected to be around 2500’ which means heavy snow in the upper elevations. This storm will see another round of strong Easterly winds, but winds are expected to decrease in the afternoon as the storm front passes.

 *Seattle Ridge weather station was heavily rimed and the anemometer (wind sensor) was destroyed. We are currently working to replace it.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 34  0.4  53
Summit Lake (1400') 36  rain  0.1  20 
Alyeska Mid (1700') 33  3" wet snow  1.16  40 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 25 ENE  33  98 
Seattle Ridge(2400') 30  *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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