Turnagain Pass

GENERAL ANNOUNCEMENTS

Good Morning backcountry travelers, this is Carl Skustad with the Chugach National Forest Avalanche Information Center on Friday, February 6, 2009 at 7am. This will serve as a general backcountry avalanche advisory issued 5 days a week Wednesday-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…

-General Weather Observations-

Not as much snow fell as forecasted in the advisory area. The Prince William Sound based low delivered 4″ in the Girdwood Valley, ~7″ midway at Alyeska and ~8″ atop Alyeska. More snow may have fallen in Portage but only an inch fell in Turnagain Pass. Moose Pass and Summit Lake looks to have picked up a couple inches. Strong winds gusted in the 40’s yesterday afternoon as the front moved through.

–The DOT weather station near the crest the highway at Turnagain Pass at 1000 feet–

Is recording a temp of 15 degrees (2 deg cooler than yesterday) with light SW winds.

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

Has a temp of 18 degrees (1 degree warmer than yesterday). 1 ” new precip. Total snowpack depth is 64″ after 1 inch of settlement.

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

Shows a temperature of 15 degrees (1 degrees warmer than yesterday). Winds have been light to moderate averaging 5-15 mph out of the W with a max gust of 49 mph yesterday afternoon.

-Surface Analysis Maps-

The 1000 mb low that gave us yesterday’s snow is dissipating into the Copper River Basin. AnCNFAIC Staff weak low is moving our way from the east.

-Radar-

Mostly clear, with scattered showers over Valdez and Cordova. By the look of the stars outside this early morn I believe it!

AVALANCHE HAZARDS

Primary avalanche concerns

-Surface wind slabs on slippery bed surface on alpine ridges above 3000 feet

Secondary avalanche concerns

-Rain crust (ice layer) from January below 3000ft

AVALANCHE AND SNOWPACK

Bottom Line

Normal Caution is still advised for the advisory area today with pockets of increased hazard on leeward, alpine ridges were wind slabs are present. We also need to increase the avalanche hazard from 800 to 1500 feet due to an increased number of human triggered avalanches in this suspicious elevational band.

Discussion

Heavy rains slammed the area 4 weeks ago. This rain left behind a rain crust up to ~3000ft. This crust is 1 to 1.5 ft deep at 1000 ft. A slight temperature gradient has formed around this crust in the last couple of weeks, most significantly between 800 and 1500 ft. This temperature gradient has developed weak faceted snow around this crust. My main concern with this band exists if you found yourself above terrain traps at these low elevations.

Of more concern to me is the higher elevation wind slabs. These are obvious and predictable. If the snow looks fat and wind loaded, it’s a wind slab. The good thing is we know where they live and they’re predictable. We can stay away from them if we choose. Yesterday’s strong winds re-energized these slabs. An experienced skier triggered a side loaded, alpine wind slab two days ago at 3900 ft on Tincan Proper. This skier was savvy enough to have an escape off the slab as it cascaded 2000 ft to the valley floor. This slab had a typical size of 12 inches deep and 75 feet wide. I have seen or heard of these wind slabs running on multiple aspects over the last week. Shooting cracks and drum sounding snow will indicate wind stiffened snow and a possible wind slab. If these conditions are present, lower you slope angle or return to softer, lighter snow.

You can see the wind slab propagating under this skiers feet. 3900 ft on Tincan Proper, south aspect. 12″ deep, 75 ‘ wide, ran 2000’.

WEATHER FORECAST

WESTERN PRINCE WILLIAM SOUND-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKST FRI FEB 6 2009

.TODAY…MOSTLY CLOUDY. SCATTERED SNOW SHOWERS IN THE MORNING…

THEN A CHANCE OF SNOW IN THE AFTERNOON. HIGHS IN THE MID 20S TO

LOWER 30S. LIGHT WINDS EXCEPT WEST 10 TO 20 MPH NEAR WHITTIER.

.TONIGHT…MOSTLY CLOUDY. A CHANCE OF SNOW IN THE EVENING…THEN

SCATTERED SNOW SHOWERS AFTER MIDNIGHT. LOWS 15 TO 25…COOLEST

INLAND. NORTHWEST WIND 10 TO 15 MPH.

.SATURDAY…PARTLY CLOUDY. HIGHS IN THE 20S…COOLEST INLAND.

NORTHWEST WIND 10 TO 15 MPH EXCEPT NORTH 15 TO 25 MPH NEAR

SEWARD.

.SATURDAY NIGHT…MOSTLY CLOUDY. LOWS 10 TO 20 ABOVE…COOLEST

INLAND. NORTHWEST WIND 10 TO 15 MPH.

.SUNDAY…MOSTLY CLOUDY IN THE MORNING THEN BECOMING PARTLY

CLOUDY. HIGHS IN THE LOWER TO MID 20S. NORTHWEST WIND 10 TO

15 MPH EXCEPT NORTH 10 TO 20 MPH NEAR SEWARD.

TEMPERATURE / PRECIPITATION

SEWARD 32 24 29 / 60 40 0

GIRDWOOD 33 16 21 / 40 20 0

This concludes today’s avalanche advisory the next advisory will be on Saturday, February 7th. Thanks and have a great day.