Turnagain Pass Avalanche Forecast

GENERAL ANNOUNCEMENTS

Good Morning backcountry travelers, this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Saturday, March 7, 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. This advisory expires in 24 hours and does not apply to operating ski resorts or highways/railroads.

MOUNTAIN WEATHER ROUND UP FOR THE LAST 24 HOURS

-General Weather Observations-

Zero precip in past 24 hours for Summit, Grandview, Turnagain Pass, or Girdwood. Winds have been strong. Max’s recorded a gust of 74mph. Sunburst was the least windy weather station, but the winds have still been strong enough to transport snow. Temps are colder at all weather stations from Summit Lake to Turnagain Arm by 4-20 degrees.

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

Has a temp of 13 degrees (7 degrees colder than yesterday). Zero new water and zero new snow. Total snowpack depth is 69″.

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

Is recorded a temp of 5 degrees (6 degrees colder than yesterday). Winds have been light to moderate averaging 9-17 mph out of the NW, with strong gusts up to 36mph.

-Surface Analysis Maps-

Between 3am and 9pm yesterday….Show that high pressure from yesterday building strength (1043-1047mb)moving east into the Gulf of Alaska. The storm behind high pressure has been getting weaker (978-992mb) as it has moved east toward us. Its just under the Aluetians.

-Radar/Satellite-

Radar is clear this morning, but the satellite shows an arm of moisture getting pulled up from the south from that next storm. That moisture is not too far to our west.

AVALANCHE HAZARDS

Primary avalanche concerns

-Sea-level to at least 3200′ (Probably higher). New eggshell crust was observed in Girdwood, Turnagain Pass and Summit Lake on 3/5/09. It was everywhere on all aspects and could become very dangerous if it gets buried with more than 1 foot of slaby snow.

-Below 3000 feet. Rain crust buried under 1-4 feet of surface snow. There is a layer of weak sugary faceted snow on top and below this hard rain crust. We are still finding moderate to hard instability on top of this crust in our stability tests. This crust is showing signs of being a very persistent weak layer.

-Above 3000 feet. We’ve been finding a clean shear about 1-2 feet deep. Buried surface hoar has been reported in some but not all pits.

AVALANCHES AND SNOWPACK

Bottom Line

Elevated Caution is advised today due to new windslabs on top of that eggshell crust. Medium sized human-triggered avalanches are likely today. Plus that clean shear we’ve been seeing in top 1-2 feet of snow above 3000 feet might be more reactive on slopes steeper than 35 degrees today due to yesterday’s wind. The rain crust below 3000 feet is not likely to avalanche right now but it is still a serious concern and has the most potential for large avalanches. A big red flag for this lower elevation weak layer will be if we ever get rain on the snow.

Discussion

Yesterday’s wind is the big story. Natural avalanches, including cornice breaks, were reported from Girdwood to Summit Lake that occured during the strong wind yesterday. The wind has backed off a bit, but its still moving out there. Natural avalanches will be less likely today, but human-triggered avalanches on new wind slabs will be likely.

That new eggshell crust that formed on the surface Wednesday night 3/4/09 will provide a slick bed surface for these new windslabs to avalanche. We recieved a report yesterday that this eggshell crust formed in the Summit Lake area as well. This layer makes me nervous. It provides a consistant bed surface which encourages wide propogation. Its on all aspects and elevations that we ski, snowboard, and snowmachine on.

That clean shear up high that we have been observing in the top 1-2 feet of snow that sometimes has been identified as buried surface hoar has more potential for problems today. This layer should heal up fairly fast because its not consistant across the entire range. Those new windslabs, however, could step down to this older weak layer today.

Down low (below 3000 feet), That sugary faceted snow (mixed forms) on top of that rain crust is still a problem that is not showing signs of going away. We will see avalanches on this weak layer before the season is done. Watch out if it ever rains at these lower elevations.

As you can tell, this advisory is very wordy and we are talking about multiple problems. You should take that as a sign that our snowpack is not in the best shape right now. Sunny Saturday’s immediately following a storm are a very very common time that people let their guard down and get caught in avalanches. Remember that most avalanches occur during our within 24 hours of a storm. We are still in that window due to yesterday’s wind. There will be plenty of places to travel safely today; but, this is NOT one of those times when you can wildly attack the mountains. These new windslabs should be very reactive due to that new crust and can be big enough to bury a person. Strict adhearance to travel rituals are the key to staying safe. Traveling one at a time, watching your partners, and staying spaced out are some of the strategies that will help keep you and your friends alive. Bring your inclometer. If you are on slopes steeper than 35 degrees, then you are in terrain that has the most potential for triggering one of those landmines.

WEATHER FORECAST

WESTERN PRINCE WILLIAM SOUND-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKST SAT MAR 7 2009

.TODAY…MOSTLY SUNNY. HIGHS IN THE LOWER 20S TO LOWER 30S.

NORTH TO WEST WIND TO 15 MPH. GUSTS TO 35 MPH NEAR SEWARD AND

WHITTIER IN THE MORNING.

.TONIGHT…PARTLY CLOUDY IN THE EVENING THEN BECOMING MOSTLY

CLOUDY. LOWS ZERO TO 20 ABOVE…COLDEST INLAND. VARIABLE WIND

TO 10 MPH EXCEPT NORTH WIND 10 TO 20 MPH NEAR SEWARD.

.SUNDAY…MOSTLY CLOUDY. HIGHS IN THE MID 20S TO LOWER 30S.

VARIABLE WIND TO 10 MPH.

.SUNDAY NIGHT…MOSTLY CLOUDY WITH A SLIGHT CHANCE OF SNOW.

LOWS 15 TO 25. EAST WIND 10 TO 20 MPH.

TEMPERATURE / PRECIPITATION

SEWARD 30 15 33 / 0 0 0

GIRDWOOD 28 8 31 / 0 0 0

This concludes today’s avalanche advisory which will expire in 24 hours. The next advisory will be on Sunday, March 8th. Thanks and have a great day.