Good morning backcountry travelers, this is Lisa Portune with the Chugach National Forest Avalanche Information Center on Sunday, December 21, 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.
MOUNTAIN WEATHER ROUND UP
In the last 24 hours…
-The Center Ridge weather station at 1800 feet in Turnagain Pass recorded no new snow for a total snowpack depth of 52 inches. The temperature this morning is 15 degrees F (12 degrees colder than yesterday).
-The Sunburst weather station at 3800 feet in Turnagain Pass and Max’s weather station at 3200 feet in the Girdwood Valley both recorded light and variable winds yesterday. Ridgetop winds are currently light with temps ranging from 18-20 degrees F (2-5 degrees colder than yesterday).
Happy Winter Solstice to everyone!! We’ll have a grand total of 5 and ½ hours of daylight today to get out and enjoy the snow and sunshine. Just 2 inches of snow has fallen since Dec. 10, and fortunately the winds have been light except for a 20 hour period Friday and Saturday when they averaged about 15-25 mph out of the east. The snowpack at Turnagain Pass has settled about 20 inches since our last big snowfall 11 days ago when the Girdwood Valley got 50 inches of snow and the pass got about 30 inches.
Expect sunny skies today, fog down low, light winds, and ridgetop temps in the high teens. You may find stronger NW winds closer to the coast. Our next chance for snow looks to be tomorrow and Tuesday before anCNFAIC Staff ridge of high pressure builds in mid-week.
1. Persistent Weak Layers of buried surface hoar and sugary October facets at the bottom of our snowpack continue to be a concern and will be for some time. These layers are responsible for most of the human-triggered avalanches so far this winter and are triggered from thin, shallow areas of the snowpack.
2. Glide cracks have made a resurgence over the last few weeks mainly on south and west aspects, and some of them have avalanched as recently as yesterday in the Girdwood Valley. Avoid traveling underneath them as it is impossible to predict when and if they will release.
AVALANCHE AND SNOWPACK DISCUSSION
Just a few touchy windslabs were reported yesterday in Turnagain Pass, mainly confined to the ridgetops, but they seemed to stabilize pretty quickly once the winds subsided. Thankfully the strong northerly winds usually associated with high pressure have spared us, and the snow conditions have remained stellar with top to bottom powder. One of our observers reported finding an instability on an icy layer about 1.5 feet down at 1700′ elevation on Eddies that failed on a Rutschblock 3 but with a rough shear. This icy layer probably formed during our warm rainy spell the first week of December and was quite possibly the layer that failed in the snowmachiner-triggered avalanche on Dec. 11.
It has been just over a week since our last reported human-triggered avalanche when a skier was completely buried on the south face of Cornbiscuit. That same day a skier remotely triggered an avalanche on the SE Face of Superbowl Peak, and multiple parties reported widespread whumphing on N-E-S aspects in the same area. Both of these avalanches ripped out to the ground, failing on the sugary faceted snow and surface hoar that formed in October. They did not, however, propagate across the entire slope, staying confined to isolated terrain features.
We are still dealing with a shallow, early season snowpack in some areas, especially on the southern end of Turnagain Pass and near Summit Lake. The fact is most of our entire advisory area has weak faceted snow buried near the ground. In some areas it is buried under 10+ feet of snow and CNFAIC Staffs only 2-3 feet. It is in these shallow areas that human-triggered avalanches are most likely to occur because the weak layer is closer to the surface and thus more easily impacted. Although our snowpit results continue to show good stability on this layer, there are still pockets of instability that could catch someone off guard.
Likely areas to trigger an avalanche are:
-Higher elevation windswept aspects where the snowpack remains cold, shallow, and weak
-Shallow rocky slopes
-Wind-scoured ridges where the snowpack tapers from shallow to deep
Terrain management is the key to staying safe when dealing with the spacial variability of deep-slab instabilities and shallow areas of the snowpack. In CNFAIC Staff words, it is still too early for big exposed complex lines. Use good travel habits and evaluate the snow depth and terrain carefully.
This concludes today’s advisory; the next advisory will be Wednesday, December 24th. 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 21 2008
.TODAY…PARTLY CLOUDY. PATCHY MORNING FOG. HIGHS IN THE LOWER 20S TO
LOWER 30S…COOLEST INLAND. VARIABLE WIND TO 10 MPH. NEAR SEWARD AND
WHITTIER…NORTH AND WEST WIND 20 TO 30 MPH.
.TONIGHT…MOSTLY CLOUDY. LOWS IN THE LOWER TEENS TO LOWER 30S…
COOLEST INLAND. LIGHT WINDS EXCEPT NORTH 10 TO 20 MPH NEAR
.MONDAY…SNOW. SNOW ACCUMULATION 1 TO 4 INCHES. HIGHS IN THE
MID 20S TO LOWER 30S. VARIABLE WIND TO 10 MPH.
.MONDAY NIGHT…SNOW LIKELY. LOWS 15 TO 25. LIGHT WINDS.
.TUESDAY…SNOW LIKELY. HIGHS IN THE MID 20S TO LOWER 30S. VARIABLE
WIND TO 10 MPH. NEAR SEWARD AND WHITTIER…NORTH AND WEST WIND
INCREASING TO 15 TO 30 MPH.
TEMPERATURE / PRECIPITATION
SEWARD 31 23 29 / 0 0 100
GIRDWOOD 20 15 27 / 0 0 80