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ARCHIVED - Forecasts expire after 24 hours.
Issued
Thu, December 11th, 2008 - 7:00AM
Expires
Fri, December 12th, 2008 - 7:00AM
Forecaster
CNFAIC Staff
Avalanche risk The Bottom Line

GENERAL ANNOUNCEMENTS

Good morning backcountry travelers, this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Thursday, December 11, 2008 at 7am. This will serve as a general backcountry avalanche advisory issued for the Turnagain Arm (Turnagain Pass is the core advisory area). Local variations always occur. Note: We are now issuing regular advisories 5 days a week Wednesday-Sunday.

INTERAGENCY AVALANCHE RESCUE TRAINING

On the weekend of December 13-14, there will be an avalanche rescue training taking place this weekend at Turnagain Pass. Please be aware of rescue workers, helicopters, rescue snowmachines and areas set up for rescue training drills. Thanks.

MOUNTAIN WEATHER ROUND UP

In the last 24 hours…

-The Center Ridge weather station at 1800 feet in Turnagain Pass-

Recorded .1 inch of water and 1 inch of new snow. Current temperature is 18 degrees F (3 degrees colder than yesterday morning). Total snowpack depth is 64 inches, with a total of 5 inches of settlement since yesterday.

-Sunburst weather station at 3800 feet in Turnagain Pass-

Recorded light winds averaging 3-11 mph from variable directions with a moderate gust of 22 mph. Current temperature is 11 degrees F (10 degrees colder than yesterday)

-Surface Analysis Maps-

From 3 am Wednesday to 9pm last night, showed that same storm that dumped on us is still hanging around. It continued to stall out in some sort of eddy just south of Prince William Sound. It has gotten very weak (991Mb-1014Mb). There are a couple of new storms by Russia.

-Jet Stream-

The analysis from 9pm last night showed the main flow streaming from west to east and heading right towards Juneau. The forecast predicts shift in the next 24 hours and start flowing from north to south.

-Satellite-

As of 6:00 am this morning… it looks pretty boring. It does not look like there is anything over us worth talking about.

-Radar-

The Middleton radar is working again. It shows a wall of light precip from Valdez past Cordova. Its moving east

-General Weather Observations-

Ridge top temperatures are colder this morning than yesterday by 7-10 degrees. Sea-level temps are warming today than yesterday by 2-5 degrees. Winds have been very calm in the past 24 hours.

PRIMARY AVALANCHE CONCERNS

-Terrain Management

AVALANCHE AND SNOWPACK DISCUSSION

Carl and I had some grey-bird visibility yesterday and saw natural avalanches that appeared to rip out during the storm because they were filled in with some new snow. The biggest one was on Todd’s Run on the north side of Tincan (see photo gallery). The next biggest natural avalanche was on the eastern aspect of Sunnyside accross from the motorized parking lot (see photo gallery). We also saw numerous small to medium natural avalanches on Sunburst, Magnum, Cornbiscuit and Lipps. Plus, a good sized glide crack has formed on the southwest aspect of Lipps right in the middle of my favorite ski run on that mountain (see photo gallery). The south and southwest aspects of Magnum had numerous natural avalanches on steep rollovers at mid elevations. Plus, I’m not 100% sure, but it looked like there was a very deep crown face on the Southwest aspect of Magnum under the cornice. It was really filled in, but I’ll bet that was a large natural avalanche.

DOT triggered a good sized class 3 avalanche with artillery yesterday along Bird Flats yesterday that left a large debris pile at the bottom.

Here’s the facts…

-Those week October facets failed on multiple aspects during this past storm.

-Big terrain with large bowls near wind scoured ridges seemed to produce the largest avalanches.

-Artillery was able to trigger some large avalanches yesterday afternoon.

-The snowpack has settle 5 inches in the past 24 hours, temps have cooled down, winds have been light, and there has been no additional loading.

It appears that the right kind of trigger, like a big storm or artillery can still create avalanches on those October facets. Here is the big question, “Can a human trigger an avalanche today?” Well, I’ll bet that there are still some dangerous avalanche conditions on some terrain features; so, it will be important to evaluate your snow an terrain carefully and use good travel habits. Let’s slowly ease back into the mountains, stay away from big lines, and watch our slope angles today.

WATCH OUT SITUATIONS

-Rocky terrain with shallow snow connected to deeper snow

-Steep rollovers (check out the photo gallery picture of Mangum)

WEATHER FORECAST

WESTERN PRINCE WILLIAM SOUND-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKST THU DEC 11 2008

.TODAY…MOSTLY CLOUDY WITH SCATTERED SNOW SHOWERS. HIGHS IN THE

20S. NORTH TO WEST WINDS 10 TO 20 MPH. GUSTS TO 30 MPH NEAR SEWARD

AND WHITTIER.

.TONIGHT…PARTLY CLOUDY. LOWS IN THE MID TEENS TO LOWER 20S.

WEST TO NORTH WINDS 10 TO 20 MPH. GUSTS TO 40 MPH NEAR SEWARD AND

WHITTIER.

.FRIDAY…INCREASING CLOUDS. HIGHS IN THE UPPER TEENS TO MID 20S.

NORTH TO WEST WINDS 10 TO 20 MPH. GUSTS TO 40 MPH NEAR SEWARD AND

WHITTIER IN THE MORNING.

TEMPERATURE / PRECIPITATION

SEWARD 25 18 24 / 20 0 0

GIRDWOOD 24 15 21 / 40 0 0

Thu, December 11th, 2008
Alpine
Above 2,500'
0 - No Rating
Avalanche risk
Treeline
1,000'-2,500'
0 - No Rating
Avalanche risk
Below Treeline
Below 1,000'
0 - No Rating
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.