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Snow & Avalanche Weekly Summary

Summit Area
Forecaster:   Wendy Wagner  
Saturday, December 20th 2014
Created: Dec 20th 8:17 am
Summary and Current Conditions

If you have been reading the Turnagain Pass advisories during the past week then you have a good idea what is going on in the Summit Lake region; dangerous avalanche conditions exist. After a warm 3 day storm brought variable amounts of snow (5"-20") with strong Northeasterly winds to elevations above 2,000', a widespread natural avalanche cycle ensued. Although the natural avalanche activity ceased with the storm on Wednesday Dec 17th, human triggered avalanches did not. This is due to the new snow resting on a layer of buried surface hoar that sits roughly 10-18" below the surface. More on that below.

If you are getting out into the Summit Lake zone, watch your slope angles. Travel on slopes steeper than 35 degrees is not recommended. Slab depths are thin (10-18") which makes triggering an avalanche theoretically easier here than in the Turnagain Pass area. 


Recent Avalanche Activity:

Thursday, Dec 18th: Large remotely triggered avalanche on the Northern steep aspects of Manitoba Mountain. This avalanche was triggered from the lower angle terrain facing West (common westerly slope of Manitoba) by a skier causing a collapse that propagated around the ridge and subsequently pulled out three Northerly bowls. Photo below and a great write up was sent in and you can see it HERE.

North chutes of Manitoba remotely triggered avalanche (12/18/14, 3,400' on SW-NW slopes, 40 degrees to 40+)

 

Other avalanche activity associated with the storm consisted of large natural avalanches running to valley bottoms in some locations. See Alex's write ups HERE and HERE.


Primary Concern

Total snowpack depth in the Summit Lake area increases dramatically with elevation -  5-8" sits at 1,500' with up to 4' at 3,500'. The snow surface is soft settled powder and quality skiing and snowboarding has been reported.

At elevations above 2,500', sitting roughly 10-18" below the recent storm snow is a layer of buried surface hoar that has proven to be reactive. Though we have only a small amount of information for this region, we do have bull's eye data - the avalanche on Manitoba Thursday.

Buried surface hoar is one of those persistent weak layers that can take days, or weeks, to gain strength and give us confidence to venture onto the steeper slopes. With the consequences high in the event an avalanche is triggered, the risk vs. reward just isn't there for many of us. A fun day with good snow conditions can be found on lower angle slopes.


Secondary Concern

Winds on Thursday and Friday have been strong enough to move the new snow around and form wind slabs and drifts. This concern is trumped by the primary concern above, yet is worth noting for two reasons. One, it adds additional load to the slab resting on the buried surface hoar. And two, wind slabs may be found below 2,500' where triggering a larger slab is less likely.


Mountain Weather

Over the past week, the Summit Lake area has seen a warm and windy storm that deposited roughly 5-15" of snow above 2,000' from Dec 14th through Dec 17th. Snow depths with this storm were quite variable and winds were strong from the Northeast. The rain/snow line was ~1,500'.

Thursday and Friday skies cleared up and temperatures remained warm (low 30's at 1,200' and mid 20's at 3,000'). Winds toward the end of the week have been moderate to strong from the Northeast.

For Saturday we should see partly cloudy skies with moderate NE winds. Temperatures should be in the mid 20's F.

Sunday, there is a chance for snow, it is too early to say how much, along with moderate Easterly winds. 

As always, check our Weather Page for the most up to date conditions.  Fresno Ridge and Summit Lake SNOTEL sites are the most pertinent stations to check before heading out for the day.

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 20, 2014 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: Closed
Placer River: Closed
Skookum Drainage: Closed
Turnagain Pass: ClosedWe are still lacking sufficent snow at highway elevations. Continue to check back here for the latest info on motorized openings on the Chugach National Forest.
Twentymile: Closed
Seward District
Carter Lake: Closed
Lost Lake Trail: Closed
Primrose Trail: Closed
Resurrection Pass Trail: Closed
Snug Harbor: Closed
South Fork Snow River Corridor: Closed
Summit Lake: Closed

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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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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