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Snow & Avalanche Weekly Summary

Summit Area
Forecaster:   CNFAIC Staff  
Saturday, April 1st 2017
Created: Mar 30th 22:55 pm
Summary and Current Conditions

*Dangerous avalanche conditions exist in the Summit Lake zone.*
Up to a foot of new snow with strong winds are creating an unstable snowpack - natural avalanches have been occurring since Thursday night, March 30th. Expect natural and human triggered avalanches to be likely while the storm cycle continues - possibly into early next week. Travel in avalanche terrain is not recommended.

UPDATE: Saturday April 2nd:  One human triggered avalanche (Manitoba) and two natural avalanches. Photos below and report HERE.

Skier triggered slab avalanche on the Southerly aspect of Manitoba while making a turn along the ridgeline and dippin a bit on the Southerly face.

Below are two natural slab avalanches that occured sometime on April 1st or 2nd. Butch Mt slide below.

Fresno slab that pulled out deeper layers.

 

Original Summit Summary:

Images below are of natural avalanche activity on Friday, March 31st in the Summit Lake area. These slabs are likely composed of the recent storm snow and 1-2' thick. Photos: Alex McLain

          

 

SNOWPACK SUMMARY:

Springtime change is in the air throughout the Summit Lake area. After another warm sunny weekend, storm cycles began to hit the area by mid-week leaving 10" of new snow by Friday, March 31st. This was accompanied by winds strong enough to transport the new snow and keep ridgelines in the alpine bare. Warming temperatures were also present, climbing to the mid-30s F. Two avalanches were noted last week; one skier triggered sluff on Tuesday off the West aspect of Butch as well as an avalanche off the South aspect of Tenderfoot, likely from the mid-week storm. 

Even with the new snowfall, Summit Lake continues to have a very thin and poorly structured snowpack. The recent warm snowy weather, paired with the poor structure, is adding significant strain to the snowpack. With more storm systems lined up in the coming week, extra attention and caution is warranted. For humans traveling in the backcountry, it will be important to stack the odds in your favor by making conservative terrain choices (slopes under 35 degrees) and being extra observant of changes in the weather and snowpack - as these are signs that avalanche potential may be increasing. Additional snowfall, rain, wet saturated surface snow, or continued high winds are likely to keep the scales tipped as natural avalanche are occurring currently. So far activity has been composed of just the storm snow, but far propagating avalanches that have the potential to step down into weak layers at the base of the snowpack may occur, creating a much larger avalanche. 

*During the week, stay tuned on the most current up to date avalanche and weather conditions on the Turnagain Pass daily advisory and the Summit Lake Observations Page! Also, Please help us keep tabs on the Summit area - if you see any avalanche activity send us an observation HERE

Wind scoured ridges in the alpine even after the recent mid-week snowfall

 

Large depth hoar crystals (3-5mm) from the bottom of the snowpack


Primary Concern

Summit Lake has already seen 10" of new snow by Friday, March 31st, with this weekend looking to bring continued snow, warm temperatures, and strong winds. The surface before this recent storm varied from surface hoar, to near surface facets, to slick sun crust on solar aspects. It will take some time for the new snow to bond to these older weak layers. With more snow on the way, any of the below 'storm snow instabilities' are likely to be easily triggered:                                   

      • Wind slabs - slopes that are being loaded by winds
      • Soft slabs - slopes out of the wind but where enough new snow piles up to create a 'slab'  
      • Loose snow avalanches (aka, sluffs) - areas where a slab has not formed in the new snow
      • Rain? Wet snow? If this week's weather is warm enough we could see wet snow avalanches
      • Cornices - strong winds and warm temperatures will increase the likelihood of cornice falls
      • First sunny day after the storms: daytime warming can reactivate the storm snow and trigger slabs and sluffs on Southerly slopes

The above issues will become more pronounced depending on how much more snow falls and how warm temperatures get. Keep in mind, these types of avalanches could also trigger a much larger slide breaking near the ground resulting in a slab 2-4' in thickness.

Shovel tilt test showing the storm snow failing on a layer of buried surface hoar

Shooting crack from a large whumph at 1400' on Tenderfoot, Friday March 31.

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Secondary Concern

The new snow has buried yet another persistent weak layer within the Summit Lake snowpack; a widespread layer of surface hoar and near surface facets. This is in addition to the generally poor snowpack structure throughout Summit Lake. The Feb 9th buried surface hoar is still reactive and being found in pockets. Additionally, large depth hoar (3-5mm) is still present at the base of the snowpack in most locations. These weak layers may have been dormant in the past few weeks but the added load from the storm snow and increased temperatures could very easily reactivate these layers leading to avalanches that could propagate across slopes and step down to the bottom of the snowpack. 

If you are considering the Summit Lake zone when the skies clear and storms are over, remember to keep your eyes open for any signs of instability such as whumphing, shooting cracks and recent avalanches. It is also possible that little to no signs of instability may be present until an avalanche is triggered. These are all good reasons to keep your slope angles mellow, less than 35 degrees, and managing terrain you are directly on as well as the terrain above you. It may be possible to trigger a persistent slab remotely from the side or below, or once you are well onto a slope. Trigger spots will be thinner areas of the snowpack near rocks or scoured features. An avalanche occurring on one of these layers has the potential to run a long ways and take the whole slope with it.

Buried surface hoar in the pit wall at 2000' on the NW aspect of Tenderfoot.

Pit profile from 2000' on the NW aspect of Tenderfoot, March 31st.

 


Mountain Weather

Last weekend brought sunny skies and moderate temperatures to the mountains; in the 20s F during the daytime and dipping down to the teens in the evenings. By Tuesday evening the first in a long series of low-pressure systems had rolled into the area leaving 7" of new snow at Summit Lake by Wednesday morning. This snowfall was accompanied by temperatures warming to near freezing during the daytime as well as Easterly winds in the alpine strong enough to transport the newly fallen snow. Light snow continued through Thursday with another ~1" of accumulation and increased Easterly winds. Thursday evening through Friday saw another pulse of stormy weather with very strong Easterly winds along with an additional ~2" of accumulation. The winds extended down to road level with this pulse and temperatures remained just above freezing during the daytime bringing light rain to 1,200'.

Looking towards the weekend the current storm system is expected to remain in the area with temperatures increasing into the low to mid 30s Fahrenheit - rain to the parking lots at 1,400' and snow above 1,500'. Snow amounts are tough to forecast but Summit could see anywhere from a few new inches to a foot. As the weekend draws to a close, precipitation is expected to taper off though temperatures are expected stay warm; daytime temperatures in the mid-30sF. By late next week there is potential for another system to move into the area. We are beginning to feel the warmth and changing conditions brought on by spring. After the recent nearly month long spell of quiet weather and no snow it will be important to get in the habit of keeping an eye on the weather as changes brought on will play a big role in determining snowpack stability. 

For the most current weather information visit the CNFAIC weather page HERE.

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: 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

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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