Turnagain Pass

GENERAL ANNOUNCEMENTS

Good morning backcountry travelers, this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Thursday, December 4, 2008 at 7am. This will serve as a general backcountry avalanche advisory issued for the Turnagain Arm. 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 at Turnagain Pass. Please be aware of rescue workers, helicopters, and areas set up for rescue training drills.

MOUNTAIN WEATHER ROUND UP

In the last 24 hours…

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

Recorded .2 inches of water and 2 inches of new snow. Current temperature is 28 degrees F (4 degrees warmer than yesterday morning). Total snowpack depth is 47 inches.

-Sunburst weather station at 3800 feet in Turnagain Pass-

Weather station is down. Sorry about that. We will troubleshoot and fix ASAP. In the meantime, we can use CNFAIC Staff weather stations.

-Max’s weather station at 3200 feet in Girdwood Valley-

Recorded light to moderate winds averaging 8-22 mph with a gale force gust of 64 mph.

-Surface Analysis Maps-

The same storm has been hanging around out in the Aluetians since Monday morning. It has gotten weaker by a little bit since 3am yesterday (960Mb-964Mb). The center of this storm barely moved since in the last 24 hours.

-Satelite-

As of 6:00 am today, the satellite image shows that the arm of this storm is still pulling a bunch of moisture up from the south (Hawaii). Yesterday that “firehose” was pointed directly at us, now its spraying to the east of Cordova.

-Radar-

The Middleton radar shows wall of light to moderate precip hitting the outer coast to the east of the Copper River. The Kenai radar shows a wall of light to moderate precip over the Anchorage Bowl and Chugach State Park.

-Jet Stream-

The analysis still shows the main flow going south to north from Hawaii to Alaska. The forecast predicts it will shift back to a west to east flow by tomorrow morning.

-General Weather Observations-

Temperatures are warmer this morning than yesterday by 1-7 degrees at all weather stations from sea-level to 3000 feet.

PRIMARY AVALANCHE CONCERNS

-Tapered slabs of deeper dense snow on top of shallow weaker less dense snow

-buried surface hoar (about 3 feet deep)

-Rapid loading of any kind (precip, wind, temperature)

AVALANCHE AND SNOWPACK DISCUSSION

We continue to generally find a weak shallow snowpack at Turnagain Pass with a dense slab (1 finger+) about 3 feet thick on top of a less dense (4 finger) weaker layer of facets about 1 foot thick (check out the photo gallery). Plus there is a distinct layer of buried surface hoar about 3 feet deep (90-95cm). Recent stability tests have shown fair to good stability (CTM19Q235cm, CTM22Q238cm,CTH22-23Q295cm @ 3500′ Sunburst), but that is not necessarily the best information to use when deciding what to snowmachine/ski/snowboard today. Remember that these stability tests are just one piece of the entire avalanche puzzle. I think we should focus that layer of buried surface hoar and the facets on the ground. Those facets are showing signs of healing, but there is still a change in density that could fail with the right trigger. You don’t even have to dig a pit to feel that “punchy” density change, just lean into your ski pole. That surface hoar does not fail easily, but it is very clean when it does. Plus, its at at depth that is easily within the stress bulb of snowboarder/snowmachiner/skier.

The big question today is, “are human-triggered avalanches possible?” The answer is, “probably not, but it depends on the terrain.” I’m kind of guessing and being a bit conservative, but I’d say that rocky terrain steeper than 35 degrees could be the most likely scenario for a human-triggered avalanche. The size of an avalanche is most likely smaller today than it was last week, but that will change with the next rapid load. Plus, the recent natural and human-triggered avalanches in the past week have been going to the ground. Some of them were remotely triggered. Thats not good.

Basically, the snowpack is ready for a trigger. The next big storm will likely tip the balance at Turnagain Pass, which recieved quite of bit less snow than Girdwood Valley during the last storm.

WATCH OUT SITUATIONS

-collapsing or “whoomping”. If you feel or hear any of this, then get to safe terrain immediately and call it a day.

-rapid loading. The weather forecast below does not sound like anything too serious, but we need to be ready for the next big dump.

WEATHER FORECAST

WESTERN PRINCE WILLIAM SOUND-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKST THU DEC 4 2008

.TODAY…RAIN AND SNOW SHOWERS. SNOW ACCUMULATION UP TO 3 INCHES AT

HIGHER ELEVATIONS. HIGHS IN THE 30S. NORTHEAST WIND 15 TO 25 MPH

DECREASING TO 10 TO 15 MPH IN THE AFTERNOON.

.TONIGHT…SNOW AND RAIN. SNOW ACCUMULATION UP TO 2 INCHES. LOWS IN

THE UPPER 20S TO LOWER 30S. VARIABLE WIND 10 MPH. NEAR SEWARD…SOUTH

WIND 15 MPH SHIFTING TO THE NORTH AFTER MIDNIGHT.

.FRIDAY…RAIN AND SNOW. SNOW ACCUMULATION UP TO 2 INCHES. HIGHS IN

THE 30S. EAST WIND 10 TO 20 MPH.

.FRIDAY NIGHT…SNOW LIKELY. LOWS IN THE MID 20S TO LOWER 30S. EAST

WIND 10 TO 25 MPH.

TEMPERATURE / PRECIPITATION

SEWARD 36 28 38 / 80 80 80

GIRDWOOD 32 24 33 / 100 80 60