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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Heather Thamm  
Tuesday, March 28th 2017
Created: Mar 28th 6:14 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.
3 Considerable Below Treeline / Below 1,000' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
 Show the Complete North American Avalanche Danger Scale
The Bottom Line

The avalanche danger will start at MODERATE at all elevations this morning, and will increase to CONSIDERABLE by early afternoon. The forecast is calling for 6-12” of snow and ridge top winds as of 7am have increased into the 15-25mph range, (higher than originally forecasted.) Triggering a fresh storm slab 1-2’ thick or fast moving surface snow will be likely on slopes steeper than 35 degrees, but the size will be proportional to todays total accumulation. There is also a possibility that today’s snow could be adding stress to an older layer within the snowpack, increasing the possibility of triggering a larger slab avalanche. Also should the sun appear today be prepared for natural wet loose avalanches on solar aspects. 

Conservative decision making and cautious route finding will be essential today and keep an eye out for obovious clues like recent avalanches, whumpfing and shooting cracks. 

Headed to the Summit Lake area? Read the Saturday Summit Summary HERE.


Primary Concern

A series of small low-pressure systems are circulating through the Gulf and into Prince William Sound bringing snow showers to our region. Overnight 3-6” fell between Turnagain Pass and Girdwood and another 6-12” is possible today. Its also possible that parts of our forecast zone may only see a few more inches. Unfortunately these types of weak systems make for a challenging snow forecast. Yet, as we saw last week, a system such as this one turned out to produce feet of snow in the Placer Valley. This may be the case again today and the avalanche danger will depend on how much snow falls and how much the winds build today. UPDATED: As of 7am ridgetop winds have increased into the 15-25mph range and are expected to remain elevated through mid day.

Snow surface prior to this storm consisted of surface hoar with loose faceted snow underneath on shaded aspects, and a sun crust on solar aspects (SW - SE). Both of these surfaces will be hard for any decent amount of new snow to stick to. Storm related wind slabs and loose snow avalanches will be the most likely avalanche problems and are expected to be easy to initiate. 

STORM/WIND SLABS: Today's new snow and ridge top winds 15-25mph could form slabs 1-2' thick. The size of these will depend on the total amount of snow and how much the wind blows. Remember that larger terrain features could produce larger slabs and if winds stay elevated above 15mph slabs could be more conected than expected. Keep slope angles below 35 degrees and avoid terrain traps like being at the bottom of gully.

DRY LOOSE SNOW AVALANCHES (SLUFFS): Today’s snow is expected to be very loose and unconsolidated making to really easy to trigger dry loose snow avalanches on steeper terrain features protected from any wind.  Expect sluff to be fast moving and if snow totals are closer to 12” they could easily be larger and run further than expected. 

WET LOOSE AVALANCHES:  If for some reason the sun pokes out and begins to warm the snow surface to the point of melting, it will be important to watch for wet loose avalanche activity on Southerly slopes. Avoiding these areas at times of melting is recommended.

Old surfaces vary depending on aspect and elevation. On Southerly slopes a sun crust is present and in some places this crust has near surface facets on top as was the case on Lips South face yesterday.

 

 

Surface hoar ranging from small (4-6mm) to very large (1-2cm) has been well documented at all elevations on W - N - E aspects. Poor bonding is expected on these surfaces.


Additional Concern

Yesterday a skier triggering a small slab avalanche on a steep Northern chute on Orca, near Girdwood. The avalanche was actually triggered by their fast moving sluff below them, as they were stopped, letting the loose snow pass by. The slab was small, 12” deep and 20’ wide, but ran the full length of the avalanche path. This is a good reminder that some slopes harboring old slabs 1-2' thick are sitting on weak faceted snow. These slabs are composed of last week's storm snow and have mostly been eaten away with the cold temperatures - faceting to the point they are now a weak layer themselves. Yet, there are places where the slab is more consolidated, thus another reason to avoid steep slopes today if we see heavy snowfall.

 

 

Skier triggered slab on Northern chute of Orca, near Girdwood, yesterday. No one was caught in this avalanche. 


Mountain Weather

Yesterday skies were partly cloudy becoming overcast by late afternoon. Light flurries were observed during the day and scattered snow showers started late evening. Temperatures  bumped up in the afternoon into the mid 20F’s and reached 30F at road level. Ridgetop winds were light, averaging 2 mph and as of 5am have bumped up slightly from the East at Sunburst and Seattle Ridge (5-10 mph gusting to 15mph.) Overnight 6” of new snow was recorded in Girdwood and 3" in Turngain Pass.   

Today snow showers will continue and snow totals could range from 6-12” likely favoring the Portage, Placer and Girdwood. Intensity is expected to increase late morning and into the afternoon. There is also a possibility for the sun to pop out at times. Temperatures at lower elevations could fluctuate from 20F to low 30F’s with daily warming. Ridge top winds are expected to be in the 15-25mph from the East with gust in the 30's mph. 

An active weather pattern is in store for Southcentral through the next week. Snow showers are in the forecast for the next two days as a series of small lows move through the Gulf. By Thursday into a Friday a deep Pacific Low will move into our region causing heavier precipitation and warming temperatures. This will likely be rain near coastal areas and snow inland.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 24   .2 63 
Summit Lake (1400')  24 29 
Alyeska Mid (1700') 25   .22  63

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812')  20 variable 15 
Seattle Ridge(2400') 21  variable  17 

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
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