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Snow & Avalanche Weekly Summary

Summit Area
Forecaster:   Aleph Johnston-Bloom  
Saturday, December 3rd 2016
Created: Dec 3rd 5:27 am
Summary and Current Conditions

Overall the snowpack in the Summit area is shallow with only 4 inches on the Summit Lake SNOTEL at 1400'. Snowfall in late October was followed by rain all the way to upper ridgeline elevations and then a few small snow storms in early November. The avalanche season got started with a storm on November 17th that brought 6-10" to the area and landed on a widespread layer of surface hoar that developed on the cold, moist, clear nights that preceded the storm. This combination was the catalyst for a series of human triggered avalanches including two on Manitoba (more on this below in the Secondary Concern). There have been a few small weather systems that have added a few more inches of snow and/or brought sustained winds to the zone. Cold temperatures and clear weather between storms has been weakening (faceting) the shallow snowpack and will be the theme this week as the temperatures dip even more. The shallow snowpack doesn't mean there isn't enough snow to avalanche. There is definitely enough at higher elevations and weak layers that have the potential to be triggered. There was one reported glide avalanche north of Manitoba on November 25th and a few in the Turnagain area. This is a good reminder to steer clear of terrain with existing glide cracks. 

Here is a summary of surface and snowpack conditions from Wednesday, November 30th on Manitoba. Add 3-4" of new snow on top that fell Wednesday night and both an ESE wind event and strong North winds to your overall picture. 

Snow surface

Trace of new snow over soft settled snow
Above treeline the snow was wind effected and a variable mix of hard wind crust, stiff drifts and soft snow

Snowpack

1100' - 2000': 3"-1' of loose faceting snow over a melt freeze crust on the ground
2000' - 2500' 1-2' of loose faceting snow over a melt freeze crust with larger grain facets/melt forms on a melt freeze crust at ground some area have pockets of wind crust
2500' - 3400' 2-3' of snow. Buried surface hoar was found 20 cm down. There is a stout melt freeze layer 45 cm above the ground from the rain event and there is moist snow on the ground. This may have something to do with the glide avalanches.

Manitoba uptrack below 2000' and snow pit at 3100'

 

Primary Concern

Any soft snow available to transport has been blown around in the last few days. Expect hard drifted snow and scoured ridgelines at higher elevations. Leeward areas may harbor wind slabs that are initially easy to trigger or but over time be more stubborn and let you travel out onto them before breaking as the week progresses. In most cases the wind slabs are resting on older weak snow or even buried surface hoar and maybe more connected and reactive than expected. Watch out for areas that are deeper, pillowed/drifted, stiff and/or sound or feel hollow. The winds have shifted directions in the past couple days and may have loaded multiple aspects. There is a chance of more snow later in the week and this may cover up the evidence of wind loading and make it a bit harder to discern where the slabs are. 


Secondary Concern

If you have been following the advisory on Turnagain since November 19th you are well aware that buried surface hoar has been the weak layer in a series of human triggered avalanches. This same persistent weak layer is also in Summit and should be on your radar as the winter progresses and the snowpack builds. This was the weak layer in a two human triggered avalanches on Manitoba. 

 

 

Crown face of human triggered avalanche,  Manitoba November 19th.      

 Manitoba snow pit on November 30th shows the same buried surface hoar layer.


Mountain Weather

An Arctic air mass in place over the region will bring some of the coldest temperatures of the season to the area. Expect temperatures to be in the single digits and then drop down around 0F and below with the wind chill making it even colder. North winds will continue today into Sunday. There is chance for scattered light snow showers today and then clearing into the beginning of the week. Clouds will roll back in later week with a chance for snow but the forecast is uncertain. Very cold and mostly dry will be the overall theme this week. 

We are currently working on getting the Fresno weather station back online. Check the Summit Lake SNOTEL for current low elevation conditions.

Keep tabs on the Turnagain Pass advisory page as well as the Summit Lake area observations. If you get out in the Summit area we would love to hear about what you are seeing. Thanks to everyone who has already submitted observations this season!

 

This is a general backcountry avalanche advisory issued for Summit Lake Area 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: Dec 04, 2016 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: ClosedClosure order in effect due to insufficient snow cover.
Placer River: ClosedClosure order in effect due to insufficient snow cover.
Skookum Drainage: ClosedClosure order in effect due to insufficient snow cover.
Turnagain Pass: ClosedClosure order in effect due to insufficient snow cover. Conditions will be monitored daily. As of Dec 3rd 20". Cross your fingers for snow!!
Twentymile: ClosedClosure order in effect due to insufficient snow cover.
Seward District
Carter Lake: ClosedClosure order in effect due to insufficient snow cover.
Lost Lake Trail: ClosedClosure order in effect due to insufficient snow cover.
Primrose Trail: ClosedClosure order in effect due to insufficient snow cover.
Resurrection Pass Trail: ClosedClosure order in effect due to insufficient snow cover.
Snug Harbor: ClosedClosure order in effect due to insufficient snow cover.
South Fork Snow River Corridor: ClosedClosure order in effect due to insufficient snow cover.
Summit Lake: ClosedClosure order in effect due to insufficient snow cover.

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.

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If you have comments or questions regarding CNFAIC operations or winter recreation management, please email staff@chugachavalanche.org
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