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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Aleph Johnston-Bloom  
Wednesday, April 5th 2017
Created: Apr 5th 4:18 am
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.
4 High Below Treeline / Below 1,000' Travel Advice: Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
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Special Announcement

Roof avalanches have been occurring over the past week in Girdwood due to warm temperatures and rain. Be aware that roofs will continue to shed today and into this coming week.


The Bottom Line

Rising temperatures, additional rain, snow, and wind will keep the avalanche danger at HIGH again today for the Turnagain Pass area and surrounding mountains. Natural avalanches are still likely at all elevations and human triggered avalanches are very likely. Travel is not recommended in avalanche terrain. If choosing to play in the flats, make sure to steer well clear of gullies and the bottom of steep slopes in the event an avalanche releases above you.

Hiking in Portage Valley:  Avalanches occurring at the higher elevations can send large amounts of debris well into valley bottoms and cover snow-free hiking trails. Avoid trails that cross under avalanche paths. 

Summit Lake:  Travel in avalanche terrain is not recommended. Read the Saturday Summit Summary HERE.


Primary Concern

Due to periods of heavy snow, rain and strong winds, yesterday was the most active day for avalanches yet in this series of storms. A majority of the avalanche terrain that was visible below 2500' had avalanched. Much of the activity observed was wet avalanches at lower elevations. It was hard to get a good look into the Alpine. For today it is important to remember that conditions remain touchy and travel in avalanche terrain is not recommended. Avalanches may also step down into weak older layers in the pack, creating an even larger slide.

WIND SLABS and CORNICES:
Strong winds yesterday combined with heavy snow will have created large wind slabs and cornices on leeward slopes. With temperatures rising to above freezing in the Alpine these may release naturally and could entrain enough snow to run quite far. Any additional wind today will also add stress.

STORM SLAB AVALANCHES:
In areas out of the wind, expect the recent storm snow to still be reactive. Human triggered slab avalanches 2-4' thick are very likely.  

How much load is on the old weak surface from March? Storm totals (March 27 - 6am April 5th):

Turnagain Pass:     4" of H2O, 45+" of snow at upper elevations
Girdwood Valley:    5" of H2O,  55+" of snow at upper elevations
Summit Lake:         1.5" of H2O,  15+" of snow at upper elevations   

 AKRR/DOT Avalanche Hazard Reduction triggered slide in the Centerline path on the Seward Highway yesterday. 

Avalanche on Seattle Ridge across from the Sunburst parking lot.

 


Secondary Concern

Yesterday periods of heavy rain, rising temperatures and strong winds initiated a widespread wet avalanche cycle below 2500'. The rain/snow line climbed to approximately 1,500', possibly higher in places.  Many slopes across the advisory area had piles of wet debris at the bottom. Artillery triggered slabs caused long running slides that gouged into wet snow and weak deeper layers in the snowpack. Slopes that did not slide may still today as temperatures climb above freezing in the Alpine and dry snow at upper elevations becomes wet. Additional rain to 2300' will also add load and contribute to instability. In the event that the sun makes an appearance wet activity may also be exacerbated by more heat.

 

 

Avalanches along Seattle Ridge towards the uptrack.

 


Additional Concern

The balance was finally tipped and avalanches yesterday were observed stepping down into old weak layers. Dirty debris in places indicted that some avalanches were running to the ground. Prior to this storm cycle the snowpack consisted of many weak layers of facets and buried surface hoar. We may continue to see avalanches today breaking in the mid-pack or near the ground, with crown depths over 6' and running the entire length of a slide path.  

 

 

Multiple layers of buried surface hoar and facets exist within the snowpack. These layers are overloaded and avalanches are breaking into them.

 


Mountain Weather

Yesterday was cloudy and the ceiling was low for most of the day. Heavy rain and snow fell on and off throughout the day totaling around an inch of water. 6-12" of snow fell at upper elevations. Rain/snow line was approximately 1500'. Winds were Easterly blowing 20-40 with gusts into the 70s. Temperatures were in the high 30Fs to low 40Fs at sea level, 30s at mid elevations and mid to high 20s at ridgetops. Winds tapered off overnight and temperatures rose slightly. 

Today is a small lull in the system. Temperatures are forecasted to rise with temperatures at 3000' reaching 36F. The skies will be mostly cloudy with rain/snow showers throughout the day with little to no accumulation expected. Winds will be Easterly 20-30 mph with gusts into the 40s increasing in the afternoon/evening. Precipitation will pick up overnight. 

Tomorrow temperatures are forecasted to cool a little. Snow and rain showers will continue into remainder of the week with a chance for some clearer skies and sun this weekend.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 37  rain .8  85 
Summit Lake (1400') 36 rain  .2 29 
Alyeska Mid (1700') 34 rain  .65   74

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812')  26 ENE   30 71 
Seattle Ridge(2400')  29 sensor rimed  sensor rimed  sensor rimed 

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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