Turnagain Pass

GENERAL ANNOUNCEMENTS

Good morning backcountry travelers, this is Lisa Portune with the Chugach National Forest Avalanche Information Center on Saturday, December 27, 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 is still down this morning.

The Grandview weather station at 1100 feet along the railroad tracks recorded no new snow and a temperature this morning of 8 degrees F (9 degrees colder than yesterday).

-The Sunburst weather station at 3800 feet in Turnagain Pass somehow recorded light winds yesterday averaging 5-10 mph with moderate gusts in the teens and 20’s out of the NW despite numerous reports of very windy conditions throughout Turnagain Pass.

Max’s weather station at 3200 feet in the Girdwood Valley recorded light winds averaging 5-15 mph with strong gusts in the 20’s and 30’s out of the WSW.

Mile 43 Peak at 3300 feet above the railroad tracks recorded strong winds averaging 30-45 mph with gusts in the 60’s and 70’s out of the WNW.

Ridgetop winds are currently light and variable at all three locations with temps ranging from -3 to -1 degrees F (10 degrees colder than yesterday).

Mountain winds are already tapering off this morning as the low in the gulf gradually weakens and moves off shore. Portage, however, is still blowing with northerly winds averaging 20 mph. Expect mostly cloudy skies today with moderate northwesterly winds averaging 10-25 mph and ridgetop temps below zero.

BOTTOM LINE

1. Widespread wind slabs will be our primary concern today and are likely to be triggered on steep leeward aspects and cross-loaded gullies. Visibly drifting snow, shooting cracks, and hollow drum-like hard snow are the most obvious clues to wind slab formation.

2. Weak snow at the bottom of our snowpack continues to be a concern and will be for some time. Buried surface hoar and sugary October facets are responsible for most of the human-triggered avalanches so far this winter, the most recent ones occurring 2 weeks ago on Cornbiscuit in Turnagain Pass.

3. Many of the glide cracks are now covered with a thin layer of snow and may be difficult to see. A skier reported accidentally dropping into one on the south face of Cornbiscuit a few days ago. Watch your partners carefully, especially on south and west aspects where most of the glide cracks seem to have formed.

AVALANCHE AND SNOWPACK DISCUSSION

One of our trusted observers (Thanks Skip!) reported very windy conditions up at Turnagain Pass yesterday, with winds blowing out of various directions. He saw winds blowing from the north on the motorized side, cross-loading the gullies visible from the highway. He found good skiing on lower elevation low angle west aspects after getting blown off the NW ridge of Magnum. Winds on Magnum were out of the south with estimated gusts to 35 mph, producing sensitive soft slabs on northerly aspects by the end of the day. AnCNFAIC Staff one of our observers also reported strong winds from all directions up at the pass and sensitive wind slabs on leeward aspects.

There’s a lot of powder to be blown around, including the 10-14 inches of new snow that fell this past week in Turnagain Pass and the Girdwood Valley. Our most recent batch of surface hoar formed in mid-December on top of a foot of soft snow and is now sitting underneath this week’s new snow wherever it didn’t blow away. I would expect that avalanches are possible on the soft snow and surface hoar underlying recently formed wind slabs. Ski cuts should be effective with small pockets of soft wind slab but not hard slab. Hard slab allows you get out onto the slope before shattering above you and catching you off guard, whereas soft slab will fracture directly under you.

We are still tracking the weak snow at the bottom of our snowpack. This facet/crust/surface hoar medley was reactive 2 weeks ago when a skier was completely buried in an avalanche on Cornbiscuit. With no new snow or wind for a week and a half after the accident, the layer seemed to go dormant with our snowpit tests consistently showing good stability and big lines getting skied everywhere. However, the addition of this week’s new snow, plus strong winds moving even more snow onto leeward aspects, means this layer remains susceptible to avalanching due to stress from an increased load. It is also possible that avalanches triggered on surface wind slabs may step-down to the weak layers at the ground, creating an even larger avalanche.

We have noticed in the past that glide cracks tend to release during cold snaps. Be careful not to find yourself underneath one of these gaping maws, especially now that they are difficult to see.

This concludes today’s advisory; the next advisory will be Sunday, December 28th. 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 SAT DEC 27 2008

…STRONG WIND THROUGH LATE THIS AFTERNOON NEAR SEWARD…

.TODAY…MOSTLY CLOUDY. HIGHS 5 TO 20 ABOVE. NORTH TO WEST WIND

10 TO 25 MPH WITH GUSTS TO 35 MPH NEAR WHITTIER AND 50 MPH NEAR

SEWARD.

.TONIGHT…MOSTLY CLOUDY. LOWS 5 BELOW TO 10 ABOVE. NORTH TO WEST

WIND 10 TO 20 MPH WITH GUSTS TO 40 MPH NEAR SEWARD.

.SUNDAY…MOSTLY CLOUDY. HIGHS ZERO TO 10 ABOVE EXCEPT 10 TO 20

ABOVE ALONG THE COAST. NORTH TO WEST WIND TO 15 MPH WITH GUSTS

TO 35 MPH NEAR SEWARD.

.SUNDAY NIGHT…MOSTLY CLOUDY IN THE EVENING THEN BECOMING PARTLY

CLOUDY. LOWS ZERO TO 10 BELOW EXCEPT AROUND 10 ABOVE ALONG THE

COAST. NORTH TO WEST WIND TO 15 MPH WITH GUSTS TO 30 MPH NEAR

SEWARD.

.MONDAY…PARTLY CLOUDY IN THE MORNING THEN BECOMING MOSTLY SUNNY.

HIGHS ZERO TO 15 ABOVE. VARIABLE WIND 10 MPH EXCEPT NORTH 10 TO 20

MPH NEAR SEWARD.

TEMPERATURE / PRECIPITATION

SEWARD 17 10 16 / 0 0 0

GIRDWOOD 13 2 6 / 0 0 0