CNFAIC LogoCNFAIC Logo

Snow & Avalanche Weekly Summary

Summit Area
Forecaster:   Heather Thamm  
Saturday, April 8th 2017
Created: Apr 7th 23:41 pm
Summary and Current Conditions

Warm temperature, rain, snow, and strong winds associated with a series of low pressure systems impacted Southcentral, Alaska over the last week and a half. Similar to Turngain Pass, Summit Lake experienced a widespread natural avalanche cycle on all aspects and elevations. The storm total is around an 1.5" of H2O, and much of this falling as rain below 2000'.  Wednesday, April 5, was the warmest day of the cycle and temperatures reached 32F at 3800’ at MP 45 Weather Station.  Clearing skies combined with temps dipping below freezing have formed a crust in the lower elevations, but it is unknown where the snow pack transitions from a melt/freeze into dry snow. On Thursday, April 6th, strong winds were observed blowing large plumes of snow loading West and South aspects and cross loading North and East aspects - proof that dry snow was available for transport. As of Friday (4/7) there is limited information about how the new snow is adjusting to the snowpack. The most important thing to emphasize is that we are now in a spring cycle where solar radiation is impacting the snowpack during daily warming. This means the snowpack has the potential to be more dangerous in the afternoon and evening as the sun heats up the snow. 

Prior to this storm Summit Lake has had a notoriously thin snowpack with poor structure. This includes depth hoar near the ground in some areas, mid pack facets and several layers of buried surface hoar. The natural avalanches this week were likely releasing on one or all of these layers, including a human triggered avalanche on Manitoba on Sunday, April 2. Careful snowpack evaluation, caution route finding, and conservative decision making will be essential this weekend. Spring time red flag like sun triggered roller balls or wet loose avalanches will be indicators that snowpack is becoming more unstable during the heat of the day. Also be on the lookout for obvious clues like recent avalanches, whumpfing, and shooting cracks and avoid avalanche terrain should you observe any of these. 

*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

Natural avalanche in motion on West face of Tri-tip on Wednesday, April 5 at 2:30pm - of the warmest days of the storm cycle.

 

 

Slab avalanche on Manitoba, S face, triggered by skier on April 2. Luckily no one was caught. 

 

Every aspect of Moose Mountain had avalanche debris and long propagating crowns. Photo taken 4/5.

 


Primary Concern

PERSISTENT SLAB/WIND SLAB: We have been tracking advanced basal facets and depth hoar near the ground over the last few months. These layer have been the culprit in dozens of natural avalanches in the Summit Lake zone including this weeks avalanche cycle.  This is a good reason to keep your slope angles mellow and give the snowpack some to time adjust. Since this last storm arrived with strong Easterly winds, slabs thicknesses may range from 1-4’ deep. South and West aspects are likely more loaded, but East and North aspects are suspect of cross loading. It may be possible to trigger a persistent slab remotely or once you are well on to a slope. Trigger spots will be thinner areas of the snowpack near rocks or scoured features. Daily warming, direct sun light or even warm ambient air temperatures with clouds will increase the likelihood for triggering a slab. As the week progresses the likelihood of triggering a persistent slab will be decreasing, but the consiquences still remain high - should you find the right trigger spot. Remember any dramatic weather changes like rain, snow, winds, or 24 hours of above freezing temperatures could re-activate a natural avalanche cycle. 

CORNICES: Remember these unpredictable hazards can break farther back onto a ridge than expected and have the potential to trigger an avalanche in a deeper layer of the snowpack. Strong winds this week have made cornices larger and daily warming will make them more susceptible to triggering. Give cornices extra space and avoid being under them.

 

Natural avalanche on the South face of Moose Mountain - this looks to have released on deeper layers within the snowpack. 

 

Strong Easterly winds were observed throughout Summit Lake on Thurs, April 6th. The clouds sitting directly on the ridge of Raven's and Butch are actually plumes of blowing snow. 

 

Several Natural avalanches on SW face of Tenderfoot from over the last week. 

 

Snowpit at 2500' on Tenderfoot from March 31st near the beginning of the storm cycle. Note the depth hoar and buried surface hoar. 

 

 


Secondary Concern

An observer on Wednesday reported wet saturated snow up to 2500’ on Manitoba which coincided with very warm temps and light rain. On Thursday an observation from Tenderfoot reported the snow snowpack at 1600’ was completely saturated and isothermal. Since these observations there have been two nights of clear skies and below freezing temperatures which have formed a crust in the mid elevation band. In this zone it will be important to monitor this curst during the day as solar heating impacts the snow surface. If you find yourself wallowing through wet snow, avoid steep terrain. Also in the upper elevations as a sun crust begins to melt wet loose avalanches will be possible. Don’t forget that wet surface snow is a clue that the snowpack is becoming more unstable and it may be possible to trigger a larger slab deeper in the snowpack.

The snow on Tenderfoot on April 6th was wet and saturated. This was before a stout crust formed, and is a good example of dangerous wet snow conditions to avoid. Picture below is the snowpack in this location.

 

 

Although its hard to see in this picture the snowpack was wet all the way to the ground. A melt/freeze crust has now formed. Also note the weak snow at the ground and two layers of buried surface hoar. 

 


Mountain Weather

Over the last twelve days a total of 1.5” H20 fell in Summit Lake zone in the form of rain and snow. Rain/snow line fluctuated between road level and ~2500, with the warmest day occurring on April 5th. Temperatures at the road level fluctuated between upper 20F’s to mid 40F’s and in the alpine temperatures averaged in the mid 20F’s. Ridge top winds from the East have been moderate to strong, averaging 20-40mph with gusts in the 70’s at times. On Thursday, April 6th, blowing snow was observed along most ridge tops as skies were starting to clear. Overnight into Friday morning the winds had decreased and temperatures dropped to below freezing at road level. On Friday skies remained mostly clear with a daytime high of 43F and overnight temperatures remained in the upper 20F’s.  

Over the weekend scattered showers are possible and skies may vary from mostly cloudy to clear. No measurable amount of accumulation is expected. Daily temperature swings could fluctuate from low near 25F at night to highs in the mid 40F’s during the heat of the day. Ridge top winds are expected to be light, 5-10mph from the East becoming variable. This pattern is expected early into the week and possibly longer.

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.

Subscribe to this advisory:


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
© 2017 Chugach National Forest Avalanche Information Center. All rights reserved.
FCNFAIC