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Issued
Fri, April 9th, 2010 - 7:00AM
Expires
Sat, April 10th, 2010 - 7:00AM
Forecaster
CNFAIC Staff
Avalanche risk The Bottom Line

Good morning backcountry travelers this is Carl Skustad with the Chugach National Forest Avalanche Information Center on Friday April 9th, 2010 at 7 am. This will serve as 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).

ANNOUNCEMENTS

Skookum Valley and Skookum Glacier are closed to motorized vehicles (snowmachines, helicopters, ATVs) except for subsistence uses.. This closure is directed in the current Chugach National Forest Land and Resource Management Plan. Placer River Drainage remains open for motorized use to Spencer Glacier.

WEATHER ROUNDUP

Sunshine and daydreams! Expect anCNFAIC Staff clear sky day. A 1012 mb low has moved off to the east while a ridge of high pressure pushes into the area from the NW. A large low is setting up on the end of the Aluetians and will likely change our weather pattern mid weekend. The important weather note today is the lack of high temperatures yesterday. Temperatures only reached 36 degrees and below in most areas yesterday. This allowed our avalanche danger and activity to remain manageable. That means the snowpack was not truely tested.

AVALANCHE DISCUSSION

Today’s avalanche danger will start out as MODERATE, but will rapidly increase to HIGH and become VERY DANGEROUS on any sunny slopes when temperatures go above freezing.

Indications that the sun and warming are increasing the avalanche danger include: point release loose snow avalanches on the slopes you are on or adjacent to, sticky or sun effected surface snow under ski, board, or sled, and the softening of any previous surface crusts. These along with that feeling in your gut that this slope is sunny and hot should tell you to get off of avalanche terrain.

The current surface snow has not yet been tested by warm temperatures. We will see increased avalanche activity whenever the temperatures reach the high 30’s and direct sun is on the slope. We did see lots of point release avalanches yesterday and some small slabs pop out as a result of the clear skies.

The primary snowpack concern today is: intense sun and/or warm temps triggering the top 1-3 feet of new snow on top of a buried sun crust on southern aspects. We have 2 out of 3 ingredients necessary for an avalanche:

-A slab (new storm snow)

-A bed surface (slippery sun crust)

The weak layer is the missing ingredient, but that buried sun crust is smooth enough to act as both a bed surface and a weak layer especially if the sun heats up the slab on top.

Examining the new storm snow and sun crust interface on Tincan and Sunburst, we found hard failures with relatively clean but not completely smooth shear planes (for example-CTH29Q2/Q3@120cm on Tincan) on top of the most recent sun crust. There is anCNFAIC Staff shear plane about a foot deeper down with a smoCNFAIC Staff surface. CNFAIC Staff than a small collapse on a 31 degree slope when the third person stepped on to that slope, we have not been observing any obvious signs of instability.

The sun is the critical “watch out” situation this time of year. April sun and temps can change the snowpack much more drastically than January or February sun. Avalanche danger can increase rapidly to HIGH during periods of rapidly warming temps and direct sunlight especially when the sun hits fresh snow like we have right now.

Glide cracks are secondary concern today. These crevasse like features are those cracks that go all the way to the ground. Avoid traveling underneath these cracks. Glide cracks and full depth release avalanches have been occurring on warm sunny days. The most recent one occurred yesterday (Wednesday 4/7/2010).

WEATHER FORECAST (National Weather Service)

WESTERN PRINCE WILLIAM SOUND-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKDT FRI APR 9 2010

.TODAY…SUNNY. HIGHS IN THE UPPER 30S TO MID 40S. NORTH TO WEST

WIND TO 15 MPH…EXCEPT NORTH 15 TO 25 MPH NEAR SEWARD AND WEST

25 TO 40 MPH NEAR WHITTIER. WINDS DIMINISHING IN THE AFTERNOON.

.TONIGHT…CLEAR. LOWS 15 TO 25. VARIABLE WIND 10 MPH.

.SATURDAY…PARTLY CLOUDY IN THE MORNING…THEN MOSTLY CLOUDY

WITH A SLIGHT CHANCE OF SNOW IN THE AFTERNOON. HIGHS IN THE

MID 30S TO LOWER 40S. SOUTH TO EAST WIND TO 15 MPH.

.SATURDAY NIGHT…SNOW. LOWS IN THE UPPER 20S TO MID 30S.

SOUTH TO EAST WIND 15 TO 30 MPH.

.SUNDAY…RAIN AND SNOW. HIGHS IN THE 30S. SOUTH TO EAST

WIND 20 TO 35 MPH.

.SUNDAY NIGHT…RAIN AND SNOW. LOWS 25 TO 35.

.MONDAY…MOSTLY CLOUDY WITH A CHANCE OF RAIN. HIGHS IN THE 40S.

TEMPERATURE / PRECIPITATION

SEWARD 41 23 41 / 0 0 20

GIRDWOOD 38 22 39 / 0 0 0

WEATHER STATION SUMMARY for last 24 hours at TURNAGAIN PASS

3800′-Sunburst Wx Station

Temp (5am): 15 degrees F with light NW winds.

2600′-Seattle Ridge Wx Station

Temp (5am): 18 degrees F with light NW winds.

1800′-Center Ridge Wx Station

Temp (5am): 21 degrees F, yesterdays high was only 36 degrees F at 1pm. Total snowpack is 144 after 3 inches of settlement.

Thanks for checking today’s avalanche advisory. I will update this advisory by 0700 tomorrow morning, April 10th.

Fri, April 9th, 2010
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
Avalanche risk
0 - No Rating
1 - Low
2 - Moderate
3 - Considerable
4 - High
5 - Extreme
Avalanche risk Avalanche risk Avalanche risk Avalanche risk Avalanche risk
Travel Advice Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern. Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding, and conservative decision-making essential. Very dangerous avalanche conditions. Travel in avalanche terrain not recommended. Extraordinarily dangerous avalanche conditions. Avoid all avalanche terrain.
Likelihood of Avalanches Natural and human-triggered avalanches unlikely. Natural avalanches unlikely; human-triggered avalanches possible. Natural avalanches possible; human-triggered avalanches likely. Natural avalanches likely; human-triggered avalanches very likely. Natural and human-triggered avalanches certain.
Avalanche Size and Distribution Small avalanches in isolated areas or extreme terrain. Small avalanches in specific areas; or large avalanches in isolated areas. Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas. Large avalanches in many areas; or very large avalanches in specific areas. Very large avalanches in many areas.
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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.