Good morning backcountry travelers, this is Lisa Portune with the Chugach National Forest Avalanche Information Center on Sunday, December 14, 2008 at 7am. This will serve as a general backcountry avalanche advisory issued for the Turnagain Arm area (Turnagain Pass is the core advisory area). Local variations always occur.
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. Thanks.
MOUNTAIN WEATHER ROUND UP
In the last 24 hours…
-The Center Ridge weather station at 1800 feet in Turnagain Pass recorded no new snow with 2 inches of settlement for a total snowpack depth of 58 inches. The temperature this morning is 16 degrees F (15 degrees warmer than yesterday).
-The Sunburst weather station at 3800 feet in Turnagain Pass recorded light westerly winds averaging 5-10 mph with gusts in the teens for most of the day yesterday. Max’s weather station at 3200 feet in the Girdwood Valley recorded light southerly winds with a few gusts in the teens.
Ridgetop winds are currently light with temps ranging from 27-31 degrees F (12-17 degrees warmer than yesterday). There is quite the inversion this morning with Portage coming in at -10F and Girdwood at -2F.
Cold, clear weather and light winds have dominated the past three days after a strong low pressure system delivered 28 inches of snow (2.5 SWE) to Turnagain Pass and 50 inches of snow (2.9 SWE) to the upper elevations of the Girdwood Valley on Dec 8, 9, and 10. The snowpack has settled 13 inches in the last 4 days up at the pass.
Expect continued high pressure through at least Monday along with light winds. Temperatures will be a bit warmer with ridgetop temps in the 20’s.
Avoid thin, shallow areas of the snowpack where our PERSISTENT WEAK LAYERS of buried surface hoar and weak sugary October facets near the ground are closer to the snow surface and thus more easily triggered by skis, boards, or snowmachines. Rock outcrops, wind scoured ridges that taper into deeper snow, and higher colder windswept aspects should be avoided. Several human-triggered avalanches occurred yesterday in thin areas of the snowpack.
AVALANCHE AND SNOWPACK DISCUSSION
Yesterday a skier was completely buried in an avalanche on the SW face of Cornbiscuit. This slide occurred at 3500 feet elevation and had a crown face up to 5 feet deep. It was approximately 150-300 feet wide and ran 1000 feet, failing at the ground. The skier who was buried (the 3rd one down the slope) stopped to rest well below a convex rollover partway down, out of view of the CNFAIC Staff members of her party still at the top. The fourth person snowboarded down and triggered the avalanche from a shallow spot on the rollover, initially unaware that the third skier was resting partway down the slope directly below. The third skier tried to ski away but inadvertently headed toward a gully terrain trap where she was caught in the slide. Both of her skis came off, but she was still buried 5-6 feet deep. The members of her party did a beacon search and dug her out alive and uninjured in about 10 minutes. She then skied out to the road with the rest of her party. This accident had a happy ending due to the extremely fast and efficient rescue by her friends. Great job guys!!
We also received a report of a remotely triggered avalanche by a skier yesterday on the SE face of Superbowl Peak, also called Goldpan (see photo gallery). This avalanche was triggered at approximately 4000 feet elevation on a shallow rocky section of the snowpack. The slope angle near the 1-5 ft. deep crown face was 35 degrees. As the skier skinned up the ridge and out onto the slope, he tested the snowpack depth with his ski pole and felt a 2-3 inch hollow section just above the ground 30 inches down. He then backed up a couple steps, did a little hop, and heard a whumph right before the slide occurred approx. 50 feet away. This skier also reported a whumph while booting back up the east side of Superbowl Pass (between Magnum and Cornbiscuit). The snowpack depth here was 40 inches.
One of our observers reported hearing widespread whumphing on the SW aspect of Cornbiscuit, while anCNFAIC Staff skier reported a major whumph at 3100′ on a S aspect that was felt by anCNFAIC Staff party 600 feet away. Both of these skiers dugs pits in deeper sections of the snowpack (5′ and 8′) where they got clean shears on the buried surface hoar and facets near the ground, but it took 22 to 30-plus whacks on the shovel to get them to fail. What does this mean? It means you should never put blind faith your snowpit results when you hear whumphing.
The bottom line is the snowpack gets shallower and weaker the further south you go in Turnagain Pass. The mountains closer to Turnagain Arm may have twice as much snow as the peaks down by Johnson Pass. The same holds true for the Summit Lake area where the snowpack is half as much as Turnagain Pass. Shallow snowpacks are weak snowpacks, especially with buried surface hoar and facets near the ground that stick around for awhile. Many big exposed lines were getting skied yesterday, and my guess is the snowpack was just deeper and more stable on those leeward aspects. There is tremendous spacial variability in the snowpack right now, especially on the southern end of Turnagain Pass, so choose your runs carefully and listen to the snow.
Thanks to everyone who emailed photos and observations from yesterday! …Dan, Chris, Louis, and Joe…you guys rock! This concludes today’s advisory; the next advisory will be Wednesday, December 17th. If you are out in the backcountry and have the chance, please send us your observations. Simply click on “observations” next to the advisory page and fill in the blanks. Thanks and have a great day!
The weather forecast for:
WESTERN PRINCE WILLIAM SOUND-
500 AM AKST SUN DEC 14 2008
.TODAY…MOSTLY SUNNY. HIGHS IN THE UPPER TEENS TO MID 20S. LIGHT
WINDS EXCEPT NORTH TO 15 MPH NEAR SEWARD.
.TONIGHT…MOSTLY CLEAR. LOWS IN THE TEENS. LIGHT WINDS.
.MONDAY…MOSTLY SUNNY IN THE MORNING THEN BECOMING MOSTLY CLOUDY.
HIGHS IN THE MID 20S TO LOWER 30S. VARIABLE WIND TO 10 MPH.
10 MPH SHIFTING TO THE WEST IN THE AFTERNOON.
.MONDAY NIGHT…PARTLY CLOUDY. LOWS IN THE MID TEENS TO LOWER
20S. VARIABLE WIND TO 10 MPH.
.TUESDAY…MOSTLY SUNNY. HIGHS IN THE 20S. LIGHT WINDS EXCEPT
NORTH 15 MPH NEAR SEWARD.
TEMPERATURE / PRECIPITATION
SEWARD 28 20 33 / 0 0 0
GIRDWOOD 19 9 27 / 0 0 0