Turnagain Pass Avalanche Forecast

GENERAL ANNOUNCEMENTS

Good Morning backcountry travelers, this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Friday, March 13, 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-

Temps are colder at all weather stations this morning by 2-4 degrees. Temps made it above freezing to about 2000 feet yesterday, but sun effected surface snow was observed above 3000 feet yesterday afternoon on southern aspects. Winds have been light to moderate.

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

Has a temp of 22 degrees (2 degrees colder than yesterday). High temp of 34 degrees at 1pm yesterday. 0.0-0.1 inches new water and zero new snow. Total snowpack depth is 68″.

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

Is recording a temp of 16 degrees (4 degrees colder than yesterday). Winds were light averaging 1-9mph with a max gust of 18mph.

-Surface Analysis Maps-

Between 3am and 9pm yesterday….Show a storm to our SE that is getting weaker, and a couple CNFAIC Staff weak storms out to our west in the Bering Sea.

-Radar/Satellite-

Are not showing anything too drastic for our area.

AVALANCHE HAZARDS

Primary avalanche concerns

-Below 3000 feet. The “Janurary Hurricane” 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 finding DECREASING stability in spots on top of this crust. This weak layer is still showing signs of life, and probably will become very dangerous if it gets any sort of rapid load, especially rain.

-Clean shear under stiff slabby surface snow about 9 inches to 2 feet deep.

-Sea-level up to at least 3800 feet (Probably higher). The thin “glazed donut” freezing rain crust that formed 3/5/09 has been observed in Girdwood, Turnagain Pass and Summit Lake. It was everywhere on all aspects and could become a bad weak layer if it gets buried under slaby snow.

AVALANCHES AND SNOWPACK

Bottom Line

Elevated Caution is advised at all elevations. This moderate avalanche hazard is due to stiff slaby surface snow from sea-level to ridgetops sitting on top of the “glazed donut” crust and a very clean shear within the top 2 feet of the snowpack. Plus, we have a persistent deep weak layer with that “January Hurricane” rain crust that is showing signs of decreasing stability in certain spots. This weak layer has been reactive to human triggers in isolated areas, but it will probably require a big trigger like some serious weather (especially rain or intense warming) to get it to avalanche. Human-triggered avalanches are possible on isolated terrain features today. Natural avalanches are unlikely unless the sun comes out.

Discussion

We got a report of a human-triggered slab avalanche in a gully to the skiers right of “Repeat Offender” near the snowmachine up-track along Seattle Ridge. It sounded small, but it was in a bad terrain feature. We will try to follow up with more info today. Plus, over the last two days, the sun has kicked off numerous point releases. These point releases have not been observed to have stepped down to deeper weak layers or triggered any significant slabs. Southern aspects were getting baked in the sunny microwave oven yesterday creating sun crusts and melt-freeze surface snow.

The surface snow is stiff, slabby and variable. It can be challenging to ski and leads to lots of falls and body bombing. Yesterday on Magnum, we found moderate stability on top of the “glazed donut” crust CTM12Q3@10cm and different weak layer that was more difficult to trigger but it was a very clean shear about 2 feet deep. One of our observers found that same clean shear about 9-12 inches deep in a different pit on Magnum. He described this shear as almost a Q1. That jives with our pit as well. Neither of us could see anything like surface hoar. It looked like a layer of intact stellars. What ever it was, this clean layer seems to have some potential for human triggered avlanches.

That January Hurricane rain crust continues to adjust to the small amounts of weight that we continue to get slowly over time; although, the facets on top of this crust are growing. Don’t test your luck with this layer. Lisa has been digging pits every Monday for the past couple weeks at a study plot on Tincan. She has been finding decreasing stability with her shovel compression tests on top of the January Hurricane rain crust. The facets on top of that crust have become more sugary. Plus we got a report of frequent collapsing between 1200-1800 feet on Pete’s South at the southern end of Turnagain Pass. This party investigated these shooting cracks that propogated up to 70 feet long. They dug in the snow, and found that these cracks were failing on top of the Janurary Hurricane layer (see photo gallery). I was suprised on Tuesday to see how much the facets have developed at a study plot in Main Bowl along Seattle Ridge where I have been digging pits all season.

Eventually, the balance will get tipped and that layer will most likely create big avalanches. The question is where and when will this happen? The Seattle Creek Bowls and Placer/Skookum Valley slopes will be likely areas for that January Hurricane rain crust to avalanche if we every get hit with a big storm. Natural avalanches on this weak layer are unlikely today, but human-triggered avalanches are possible in the right spot. Watch out for super steep pockets below 3000 feet. Keep in mind that there is a a certain level of uncertainty with this weak layer. There is a chance the balance could get tipped with enough of these small increments of precip.

Once again, the NOAA weather forecast below does not sound like its going to pack a huge punch today, but that is exactly what we need to watch out for. Our snowpack has not had a major load for a while and it will probably not react very well whenever if it ever gets one.

WEATHER FORECAST

WESTERN PRINCE WILLIAM SOUND-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKDT FRI MAR 13 2009

…STRONG WIND SATURDAY NIGHT AND SUNDAY…

.TODAY…NUMEROUS SNOW SHOWERS. SNOW ACCUMULATION UP TO 2 INCHES.

HIGHS IN THE 30S. SEWARD AND WHITTIER….NORTH TO WEST WINDS 15 TO 25

MPH. VARIABLE WINDS 5 TO 15 MPH ELSEWHERE.

.TONIGHT…CLOUDY WITH SCATTERED SNOW SHOWERS. LOWS IN THE 20S.

SEWARD AND WHITTIER….NORTH TO WEST WINDS 15 TO 30 MPH. VARIABLE

WINDS 5 TO 15 MPH ELSEWHERE.

.SATURDAY…DECREASING CLOUDS. ISOLATED SNOW SHOWERS. HIGHS IN

THE UPPER 20S TO MID 30S. SEWARD AND WHITTIER….NORTH TO WEST WINDS

15 TO 30 MPH. VARIABLE WINDS 5 TO 15 MPH ELSEWHERE.

TEMPERATURE / PRECIPITATION

SEWARD 35 25 32 / 40 40 20

GIRDWOOD 32 24 31 / 60 40 20

This concludes today’s avalanche advisory which will expire in 24 hours. The next advisory will be on Saturday, March 14th. Thanks and have a great day.