CNFAIC LogoCNFAIC Logo

Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   John Fitzgerald  
Saturday, April 11th 2015
Created: Apr 11th 6:12 am
2 Moderate Alpine / Above 2,500' Travel Advice: Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
2 Moderate Treeline / 1,000'-2,500' Travel Advice: Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
0 NO RATING Below Treeline / Below 1,000'
 Show the Complete North American Avalanche Danger Scale
Charlie\
Special Announcement

Beginning next week, we will be issuing advisories 5 days a week.  Advisories will be posted at 7 am on all days of the week except Mondays and Wednesdays.  The final advisory of the season will be posted on Thursday April 30th.


The Bottom Line

The danger is MODERATE in the Alpine.  Areas of CONSIDERABLE danger exist on steep North facing slopes where slabs up to 3-5’ thick, while difficult to trigger, have the potential to be large and carry severe consequences.  Elsewhere it will be possible for slabs 1-2’ thick to be triggered by skiers and riders on steep slopes during the heat of the day.  Wet loose avalanches and cornices are additional hazards to avoid today.

The danger is also MODERATE in the Treeline elevations where wet slabs 1’ thick could release on steep previously wind loaded slopes.  These slabs have the potential to pull out deeper layers of weak wet snow and produce enough volume to injure or bury a person.


Primary Concern

A storm that deposited 2 feet of snow in the higher elevations 2 days ago has left slabs that are generally well bonded to underlying surfaces.  While this bonding has been good in recent tests, we saw natural slab activity after the storm had subsided.  Yesterday this occurred mainly on steep slopes that were receiving direct sun.  More of the same can be anticipated today.  Factors that will increase the likelihood of triggering will be slopes over 35º and approaching 40º, heating from direct sunlight and large triggers such as groups.  

We have limited data from North facing terrain.  As such it will be important keep slope angles 35 or lower if you find yourself on terrain facing the North half of the compass.

Natural slab activity on Seattle Ridge on steep sunlit slopes observed yesterday, April 10th.

2' Slab with a close up of the crown.  Starting zone ~2,300' SE aspect

Slab post storm Seattle 4-10-15

A view of the debris of the avalanche pictured above.  Avalanche ran ~1,000' vertical.

debris


Secondary Concern

Both wet loose and wet slab activity can be expected on steep sunlit slopes.  In the higher elevations, sun will impact slopes and “grease” the interfaces between the slab and bed surfaces.  Those bed surfaces are crusts on East, South and West aspects.
In the lower elevations, a warm and weak snowpack will allow for the chance of medium to high volume wet loose avalanches during the heat of the day.  Volume will be dictated by terrain; more sustained steep slopes will produce more debris.  
Pay attention to the temps and sun today.  Dial back your slope angles if and when you notice rollerballs, wet loose avalanches or the snow surface becomes damp and sloppy...

...or when you sink into your waist after stepping out of your skis or board:

isothermal sloppiness


Additional Concern

Weak layers of faceted snow buried as deep as 5’ sit on some slopes on North facing terrain in the Alpine.  This set up will not be found everywhere.  Because of this variability, it is especially important to treat this terrain with suspicion.  Assessment of this issue is very difficult.  The best strategy for “managing” this problem is to avoid this terrain for the time being and give those underlying weak layers ample time to adjust to the large loads (3’+ snow/3”+ H20 over the last week) that have been placed on them.  This is a low likelihood/high consequence scenario that requires patience and time.


Mountain Weather

The last 24 hours has seen the beginning of a slow and gradual exit of a large low pressure system from our area.  That system is in fact still circulating around the Gulf of Alaska.  Precipitation, winds, and temps have all diminished.  Just a trace of snow fell in the morning hours yesterday.  Winds have slowed and temps have cooled slightly overnight.

Today expect showery conditions, with occasional clouds and mostly sunny skies as that system continues to weaken and spin slowly around the Gulf.  Temperatures at 1,000’ will climb into the mid 30s F.  Winds will be calm and just a trace of precipitation will fall.  Snow showers could produce greater amounts in some areas.

The extended outlook is showing a continuation of this pattern over the next several days, as we remain under the influence of broad and weak circulation around the Gulf.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 30 trace .1 72
Summit Lake (1400') 29 0 0 12
Alyeska Mid (1700') 32 trace 0 42

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 22 ENE 7 24
Seattle Ridge(2400') 26 sensor is rimed

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: Nov 18, 2017 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: Closed
Placer River: Closed
Skookum Drainage: Closed
Turnagain Pass: ClosedOnly a few inches of snow sits at the motorized lot, not enough to open for snowmachining at this time. Updated Nov. 18, 2017
Twentymile: Closed
Seward District
Carter Lake: Closed
Lost Lake Trail: Closed
Primrose Trail: Closed
Resurrection Pass Trail: ClosedResurrection Pass trail is expected to open to snowmachine use during the 2017/18 winter season.
Snug Harbor: Closed
South Fork Snow River Corridor: Closed
Summit Lake: Closed

Subscribe to the Turnagain Area Avalanche Advisory:

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
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