Turnagain Pass

GENERAL ANNOUNCEMENTS

Good morning backcountry travelers, this is Lisa Portune with the Chugach National Forest Avalanche Information Center on Sunday, March 8th, 2009 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. This advisory expires in 24 hours and does not apply to operating ski resorts or highways/railroads.

Congratulations to Carl, Kelly, and Ava Skustad and a big welcome to their new baby boy, Aksel Lee Skustad, who was born Friday, March 6.

MOUNTAIN WEATHER ROUND UP FOR THE LAST 24 HOURS

-General Weather Observations-

This past week Turnagain Pass and the Girdwood Valley received 5-6 inches of new snow. Thursday night freezing rain coated our snowpack with a wafer-thin crust from sea level to the ridgetops, and on Friday 3/6, gale force winds out of the NW tore through the Girdwood Valley at all elevations. Strong winds also hit Turnagain Pass from a variety of directions.

Early this morning, mountain temperatures ranged from 15-17 degrees F with light and variable winds at all locations. Portage is our cold spot at 7 degrees F. Skies will cloud up today as the ridge of high pressure moves east and a 975 mb low in the northern Bering Sea slowly moves in behind. Winds will be light and variable today but will increase tonight ahead of this front and average 15-30 mph out of the east. Ridgetop temps will warm up to the high teens to low 20’s today.

-The NRCS Center Ridge weather station at 1800 feet in Turnagain Pass-

recorded no new snow. The current temp is 14F (same as yesterday) with a total snowpack depth of 69 inches.

-The Sunburst weather station at 3800 feet in Turnagain Pass-

recorded light NW winds averaging 5-10 mph with gusts in the teens and 20’s all day yesterday. The current temp is 17F (12 degrees warmer than yesterday)

AVALANCHE AND SNOWPACK DISCUSSION

Bottom Line

Human-triggered avalanches are still possible today on the new windslabs that formed during Friday’s wind event. These sensitive windslabs vary in thickness from 1-10 inches and are sitting on a slick, wafer-thin crust. Further instability is associated with a layer of weak faceted snow surrounding a thick rain crust buried 1-4 feet deep below 3000 feet elevation. For today, the avalanche danger is rated CONSIDERABLE on all wind-loaded leeward aspects steeper than 35 degrees. All CNFAIC Staff slopes have a MODERATE danger. Additional snow and strong easterly winds on Monday and Tuesday will increase the avalanche danger.

Discussion

Numerous small to medium sized (Class 1 and 2) natural avalanches occurred Friday during our little wind event. Most of these were very shallow and no more than a foot deep, but a few propagated a good distance. They seemed to be confined to north aspects on the non-motorized side of Turnagain Pass and cross-loaded easterly aspects on the motorized side. In the Girdwood Valley I noticed several on east and northeast aspects. (Check out the “General Snow Conditions” at the bottom of this page for specific locations and the “Photo Gallery” for pics) The snow that loaded lee aspects was the 2-4 inches that fell after the freezing rain crust formed Thursday night, so my guess is most of these shallow natural avalanches slid on that slick wafer-thin crust. During my tour up Sunburst yesterday I got clean fast shears and shooting cracks on any windslab sitting on top of this crust, a sure sign of instability. On windward aspects this crust was intact, exposed on the surface, and glaring in the sunshine yesterday up to 3800 feet, except in pockets near the ridgetops where strong winds ripped pieces away and exposed the powder underneath. Ridgetops and ribs were pretty windhammered.

Yesterday several of our observers dug a pit on Sunburst at 3400 feet on a SW aspect. The clean shears in the top 1-2 feet observed one week ago in this very spot seemed to have bonded together and were not reactive in stability tests. The party felt comfortable skiing slopes over 35 degrees on this particular aspect in part because the freezing rain crust was exposed on the surface and not buried.

We still have a significant weak layer buried 1-4 feet deep below 3000 feet elevation. This buried rain crust surrounded by weak faceted snow was the culprit in the majority of our natural and human-triggered avalanches the third week of February. At this point I think it would take a large trigger to get this lower elevation weak layer to fail, such as a medium to large avalanche stepping down, a pineapple express dumping feet of heavy wet snow, or rain on snow.

This concludes today’s advisory; the next advisory will be Wednesday, March 11th. If you are out in the backcountry and have the chance, please send us your observations. Simply click on “Submit a snow observation online” at the top of the advisory page and fill in the blanks. Thanks and have a great day!

The weather forecast for:

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKDT SUN MAR 8 2009

.TODAY…MOSTLY CLOUDY. HIGHS IN THE UPPER 20S TO MID 30S.

NORTH WIND TO 15 MPH IN SEWARD AND WEST WIND TO 15 MPH IN

WHITTIER. ELSEWHERE…VARIABLE WIND TO 10 MPH.

.TONIGHT…MOSTLY CLOUDY. A CHANCE OF SNOW AFTER MIDNIGHT. LOWS

15 TO 25. EAST WIND TO 15 MPH EXCEPT EAST 15 TO 30 MPH THROUGH

PORTAGE VALLEY AND TURNAGAIN ARM.

.MONDAY…SNOW. SNOW ACCUMULATION 1 TO 4 INCHES. HIGHS IN THE 30S.

EAST WIND 10 TO 20 MPH EXCEPT EAST 25 TO 40 MPH THROUGH PORTAGE

VALLEY AND TURNAGAIN ARM.

.MONDAY NIGHT…SNOW LIKELY. LOWS IN THE MID 20S TO LOWER 30S.

EAST WIND 10 TO 20 MPH EXCEPT EAST 30 TO 45 MPH THROUGH PORTAGE

VALLEY AND TURNAGAIN ARM.

.TUESDAY…SNOW LIKELY. HIGHS IN THE 30S. EAST WIND 10 TO 20 MPH

EXCEPT EAST 30 TO 40 MPH THROUGH PORTAGE VALLEY AND TURNAGAIN ARM.

TEMPERATURE / PRECIPITATION

SEWARD 32 25 36 / 0 40 80

GIRDWOOD 28 20 32 / 0 40 80