Turnagain Pass

GENERAL ANNOUNCEMENTS

Good morning backcountry travelers, this is Lisa Portune with the Chugach National Forest Avalanche Information Center on Sunday, January 11, 2008 at 7am. This will serve as a general backcountry avalanche advisory issued 5 days a week Wednesday through Sunday 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 is down. The guys from NRCS have been trying to get this fixed and have narrowed down the problem. Look for this station to be back online soon.

The Grandview weather station at 1100 feet along the railroad tracks recorded no new snow with a current temperature this morning of +2 degrees F (4 degrees warmer than yesterday). Temps climbed to as high as 20F yesterday with reports of tshirt-like 25F at the Center Ridge wx station. An inversion continues this morning with Portage coming in at -11F and Girdwood at -4F.

-The Sunburst weather station at 3800 feet in Turnagain Pass recorded winds averaging 10-15 mph with gusts in the 20’s out of the East. Max’s weather station at 3200 feet in the Girdwood Valley recorded light winds averaging 5-10 mph with gusts in the teens also out of the East.

Mountain winds are currently light and variable at both locations with temps around +15 degrees F (2-4 degrees warmer than yesterday).

It has been 18 days since our last significant snowfall. A strong blocking high has kept the jet stream to the south of us and temps below zero for the last 2 weeks. Well, change is in the air finally as a low is forecasted to track into the gulf tonight. The temps will seem downright tropical as they climb into the 20’s and 30’s tomorrow. For today expect increasing clouds, light winds except near the coast, and mountain temps in the upper teens to low 20’s. New snow accumulation of 4-12 inches is forecasted for tonight through tomorrow along with potentially strong easterly winds.

BOTTOM LINE

Conditions remain mostly stable today with a few pockets of unstable windslab near the ridgetops. Normal caution is advised. New snow, warmer temps, and stronger winds forecasted for tonight and tomorrow will increase the avalanche danger. Warmer, denser, wind-driven storm snow on top of weak cold snow means human triggered avalanches will be probable.

AVALANCHE AND SNOWPACK DISCUSSION

Our cold snap is finally coming to an end after 15 days of clear skies and sub-zero temps. The top 16-20 inches of snow consists of windslab, surface hoar, and cold faceted powder. Once buried with enough snow, this will be a significant weak layer and a thorn in our side for some time. Today the chance for a human-triggered avalanche is low, but tomorrow this will change. New snow, warmer temps, and strong winds will increase the avalanche danger.

Surface hoar has been observed from sea level to the ridgetops, with the biggest crystals found at low to mid elevations up to about 2800 feet. One of our observers found large three dimensional surface hoar up to 2100 feet on Center Ridge yesterday, which is consistent with CNFAIC Staff observations from the Girdwood Valley this past week. Smaller sized surface hoar has also been found on top of windslabs above 3000 feet.

Ben and I toured up Sunburst yesterday and found 18 inches of cold faceted powder on top of a thin crust at 2400 feet elevation that easily sheared in hand pits. One of our observers also reported finding this from 1200-2800 feet on Penguin Ridge in the Girdwood Valley earlier this week. The snow easily sluffed away even on low angles while skiing. On Thursday, a small skier triggered sluff was observed at 1300 feet on the approach to Pyramid (see photo gallery).

The windslab on Sunburst was mainly confined to the ridgetops and varied in size from 1” to 8” thick. Although I was able to punch through most of it without it fracturing, I would expect some lingering instabilities underneath these hard wind slabs due to the cold temperatures and the fact that they formed on top of weak snow. I dug down on a shallow 2 ft. deep NW aspect at 3500 feet and found the beginnings of some ugly depth hoar, but I could not get it to fracture in my stability tests. We also found that old buried surface hoar from October sitting on top of slowly strengthening facets five feet down on a SW aspect at 3500 feet. I still think these persistent weak layers warrant our attention despite not being reactive for the last 3 weeks. Large triggers like cornice breaks or CNFAIC Staff avalanches may cause these layers to fail, as well as future heavy snow loads.

This concludes today’s advisory; the next advisory will be Wednesday, January 14th. 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-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKST SUN JAN 11 2009

…STRONG WIND THIS MORNING NEAR WHITTIER…

.TODAY…CLOUDY. SCATTERED SNOW SHOWERS IN THE AFTERNOON. HIGHS

10 TO 25 ABOVE…COOLEST INLAND. VARIABLE WIND TO 10 MPH INLAND. NEAR

WHITTIER…WEST WIND 35 TO 50 MPH SHIFTING TO THE EAST 15 MPH IN THE

AFTERNOON. NEAR SEWARD…NORTH WIND 15 TO 30 MPH DIMINISHING TO 15

MPH IN THE AFTERNOON.

.TONIGHT…SNOW. SNOW ACCUMULATION 2 TO 7 INCHES. LOWS 10 TO

25 ABOVE…COOLEST INLAND. EAST WIND 10 TO 15 MPH EXCEPT NORTH

10 TO 20 MPH NEAR SEWARD. THROUGH PORTAGE VALLEY…EAST WIND 25 TO 40

MPH.

.MONDAY…SNOW IN THE MORNING…TAPERING OFF LATE IN THE AFTERNOON.

SNOW ACCUMULATION 2 TO 5 INCHES. HIGHS IN THE MID 20S TO LOWER 30S.

WEST WIND 10 TO 15 MPH EXCEPT NORTH 15 TO 30 MPH NEAR SEWARD. NEAR

WHITTIER…VARIABLE WIND BECOMING WEST 20 TO 35 MPH IN THE AFTERNOON.

.MONDAY NIGHT…PARTLY CLOUDY WITH A SLIGHT CHANCE OF SNOW

SHOWERS. LOWS IN THE MID TEENS TO LOWER 30S. LIGHT WINDS. NEAR

WHITTIER…WEST WIND 20 TO 30 MPH IN THE EVENING BECOMING LIGHT.

.TUESDAY…CLOUDY WITH A SLIGHT CHANCE OF SNOW. HIGHS AROUND 30.

EAST WIND 10 TO 15 MPH.

TEMPERATURE / PRECIPITATION

SEWARD 25 25 32 / 40 100 100

GIRDWOOD 9 9 29 / 40 60 60