Turnagain Pass

Good morning backcountry travelers this is Lisa Portune with the Chugach National Forest Avalanche Information Center on Sunday, January 2nd at 7am. This will serve as a general backcountry avalanche advisory issued for Turnagain Arm with Turnagain Pass as the core advisory area (this advisory does not apply to highways, railroads, or operating ski areas).

BOTTOM LINE

The avalanche hazard has increased to CONSIDERABLE on all windloaded slopes greater than 35 degrees. Non wind-affected slopes and rain-saturated terrain at the lower elevations will have a MODERATE danger today. Natural avalanches are possible on actively loading slopes while human-triggered avalanches are likely on steep windloaded westerly slopes above 2000 feet. Gale force winds have created dangerous avalanche conditions in upper elevation windloaded terrain, especially where new windslabs have formed over layers of buried surface hoar.

AVALANCHE DISCUSSION

Wind was the main player yesterday and will continue to be the primary troublemaker today as well. It affected mainly the mid and upper elevations where the snow was more transportable and not rain-saturated. Kevin and I found widespread slabby conditions yesterday on Tincan above 2000 feet where denser wind-driven snow was sitting on top of lighter density snow. We stuck to lower angled terrain after intentionally triggering several small avalanches on windloaded test slopes. These fresh windslabs broke about 30 feet wide and 1 to 1.5 feet deep. The video below is of Kevin doing an Extended Column Test just above the fracture line on one of the test slopes. The fast clean shear that propagated across the entire column told us what we already knew…that conditions were unstable on steep windloaded terrain.

Although we could not find any buried surface hoar yesterday, recent skier-triggered avalanches have failed on this layer. On Friday a skier triggered an avalanche on the southwest side of Sunburst around 3000 feet elevation. The slab failed on the most recent layer of buried surface hoar that formed the latter half of December…breaking 12-18 inches deep, 150-200 feet wide, and running 700-900 feet down slope. On Thursday a skier remotely triggered a slide in the Notch Mtn/Winner Creek area of the Girdwood Valley that was estimated at 100 feet wide, 1 ft. deep, and 300 feet long. The most likely culprit was buried surface hoar based on snowpit tests the next day.

The multiple layers of buried surface hoar that formed in December are highly variable in their distribution over elevation and terrain. That’s what makes this stuff so sneaky and unpredictable. Plus it tends to linger around like that last guy shooting fireworks off at 4am New Years Day. The nature of these persistent weak layers, including the facets above and below the Thanksgiving Rain Crust (TRC), will make backcountry conditions susceptible to human triggering after each new snow load or wind load.

Check out an encyclopedia of terms here: www.fsavalanche.org/Encyclopedia.aspx

WEATHER ROUNDUP

Only an inch or two of new snow fell in the last 24 hours in Turnagain Pass, but the winds were a different story all together. A deep low pressure system delivered strong to gale-force easterly winds yesterday averaging 25-55mph with a few hurricane-force gusts in the 70’s. Mountain temps were in the upper 20’s to low 30’s yesterday with the rain line generally around 1500 feet. Light rain is falling at sea level this morning while winds continue to be strong at 25-35mph out of the east. Expect continued strong winds today and light snow above 1500 feet in Turnagain Pass.

I will issue the next advisory tomorrow morning at 7am. If you get out in the backcountry give us a call at 754-2369 or send us your observations using the button at the top of this page. Thanks and have a great day.

The NWS weather forecast for:

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKST SUN JAN 2 2011

…STRONG WIND THROUGH MONDAY NIGHT THROUGH PORTAGE PASS AND

TURNAGAIN ARM…

.TODAY…RAIN…POSSIBLY MIXED WITH SNOW IN THE MORNING NEAR

TURNAGAIN PASS. SNOW ACCUMULATION UP TO 2 INCHES. HIGHS

IN THE LOWER 30S TO LOWER 40S. SOUTHEAST WIND 10 TO 15 MPH WITH GUSTS

TO 30 MPH NEAR SEWARD AND WHITTIER. EAST WIND 30 TO 45 MPH THROUGH

PORTAGE PASS AND TURNAGAIN ARM.

.TONIGHT…RAIN…POSSIBLY MIXED WITH SNOW THROUGH TURNAGAIN PASS.

PRECIPITATION MAY BE HEAVY AT TIMES. SNOW ACCUMULATION UP TO 3

INCHES. LOWS IN THE 20S TO 30S. SOUTHEAST 10 TO 15 MPH WITH GUSTS TO

35 MPH NEAR SEWARD AND WHITTIER. EAST WIND 35 TO 50 MPH THROUGH

PORTAGE VALLEY AND TURNAGAIN ARM.

.MONDAY…RAIN…POSSIBLY MIXED WITH SNOW THROUGH TURNAGAIN PASS.

PRECIPITATION MAY BE HEAVY AT TIMES. SNOW ACCUMULATION UP TO 3

INCHES. HIGHS IN THE MID 20S TO UPPER 30S. SOUTHEAST 10 TO 15 MPH

WITH GUSTS TO 35 MPH NEAR SEWARD AND WHITTIER. EAST WIND 35 TO 50 MPH

THROUGH PORTAGE VALLEY AND TURNAGAIN ARM.

TEMPERATURE / PRECIPITATION

SEWARD 35 32 37 / 100 100 100

GIRDWOOD 40 35 35 / 70 80 90

WEATHER STATION SUMMARY for Turnagain Pass:

-3800′ Sunburst Wx Station-

recorded strong to gale force northeast winds the last 24 hours averaging 30-55mph with gusts to 76mph. Temps ranged from 24F to 26F. The current temp is 25F with 36mph winds out of the northeast.

-2600′ Seattle Ridge Wx Station-

recorded strong southeast winds the last 24 hours averaging 25-40mph with gusts to 61mph. Temps ranged from 27F to 29F. The current temp is 28F with 23mph winds out of the southeast.

-1800′ Center Ridge Wx Station-

recorded 0.2” of water in the last 24 hours in the form of maybe an inch of heavy wet snow. Temps yesterday ranged from 32F to 35F. The current temp is 32F with a total snowpack depth of 59 inches.