Turnagain Pass

Good morning backcountry travelers this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Tuesday January 19th at 7 am. 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).

ANNOUNCEMENTS

There are still spots available for this weekend’s snowmachine avalanche workshop in Turnagain Pass. Sign up at the Alaska Avalanche School (alaskaavalanche.com) or call(907)345-0878. They will cover rescue procedures and snow assessments with some class room and lots of field work.

WEATHER ROUNDUP

Hindcast (Last 24 hours)

3800′ -Sunburst Wx Station-

Temps ranged between 20-22 degrees F with light average winds 4-14 mph out of the E with a strong max gust of 25mph

Current temp 21 (1 degree colder than yesterday)

2400′-Seattle Ridge Wx Station-

Winds have been calm to moderate averaging 0-18 mph out of the SE with a strong max gust of 27mph

1800′-Center Ridge Wx Station-

Temps have ranged bewteen 20-30 degrees F with zero new precip and 2 inches of settlement for a total snowpack depth of 67 inches

Current temp 22 (6 degrees colder than yesterday)

Nowcast

Temps are about the same this morning from valley floors to ridgetops in the 20’s. The temps at the weather stations on valley floors below 1800′ range between 22-25 (that’s 6-13 degrees F colder compared to yesterday). Ridgetop temps have stayed steady since yesterday ranging between 21-25 degrees F this morning. The RH is drying out up high but staying around 90% on valley floors up to 1800′. Winds are currently picking up slightly on the ridgetops with some strong gusts as high as 27mph, but average wind speeds are still light. Both the Middleton and Kenai radars shows scattered light to moderate precip moving W toward the southern Kenai Mountains.

Forecast

WESTERN PRINCE WILLIAM SOUND-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKST TUE JAN 19 2010

.TODAY…MOSTLY CLOUDY WITH A CHANCE OF SNOW. PATCHY FOG. HIGHS IN

THE UPPER 20S TO MID 30S. VARIABLE WINDS 10 MPH EXCEPT EAST WIND 15

MPH ALONG TURNAGAIN ARM AND NORTH WIND 15 TO 30 MPH NEAR SEWARD.

.TONIGHT…SNOW LIKELY. SNOW ACCUMULATION UP TO 4 INCHES. LOWS IN THE

LOWER 20S TO LOWER 30S. COLDEST THROUGH MOOSE PASS. EAST WIND 10 TO

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

.WEDNESDAY…MOSTLY CLOUDY WITH A CHANCE OF SNOW. PATCHY FOG.

HIGHS IN THE UPPER 20S TO MID 30S. LIGHT WINDS EXCEPT NORTH WIND 10

TO 20 MPH NEAR SEWARD.

Temperature / Precipitation

SEWARD 34 27 34 / 30 60 40

GIRDWOOD 36 26 30 / 30 60 30

Short Term Weather Model Forecasts (NAM, WRF, GFS) for the Kenai Mountains near Turnagain Pass

Sea-level: GFS shows 0.25 inches of water forecasted today

3000′: temps forecasted between 23 and 32 degrees F with winds 5-15 mph

6000′: temps forecasted between 14 and 23 degrees F with winds 20-30 mph

AVALANCHE DISCUSSION

Today’s weather should not contribute to the avalanche danger today at Turnagain Pass.

The main avalanche concern today is that slippery rain crust underneath the 1.5-2.5 feet of newer snow especially between 2000′-3000′. This slippery rain crust formed on Thursday Jan 7 and is widespread on all aspects from Girdwood to Summit Lake.

Over the past week, our pit data/observations from both sides of the highway at Turnagain Pass from Magnum, Sunburst, Repeat Offender, Warm Up Bowl, and Tincan have found some variability in this crust. We have found crust sandwiches, single crusts, thin breakable crust, thick bombproof crusts, and some really rotten facets underneath the crusts in some spots. Elevation is a factor in this variability, but one thing remains constant with all of the data. Simply put, the snowpack has a poor structure right now of new snow on top of a slippery bed surface. On the CNFAIC Staff hand, stability tests have been showing moderate to hard failures with fair to good stability in test pits on the new snow/crust interface. AnCNFAIC Staff piece of the puzzle is that the new snow was still reactive to human triggers yesterday 1/18/2010 (see photo gallery). People triggered class 1 to small class 2 avalanches in Girdwood Valley, Tincan, and on the motorized side. These avalanches were about 50′ wide and did not run very far but they could be big enough to bury, injure, or kill a person if they happened on bigger terrain. Plus, we felt some collapsing on Sunburst yesterday, and anCNFAIC Staff group reported a collapse with a shooting crack at about 2600′. Upon investigation, it appears that the collapse occurred on the rotten facets underneath the crust.

Its always better to use actual data to make decisions in the backcountry, but sometimes you have to listen to your gut and apply that to your decision making process. For whatever it is worth, I personally don’t completely trust this snowpack right now for big terrain. Since it was still showing active signs of instability as of yesterday 1/18/2010, I am going to wait a little longer before getting out into bigger terrain. I think it will be wise to keep slope angles less than 38 degrees and stay away from unsupported snow fields above cliffs. The avalanche danger is decreasing today to MODERATE, but remember that the definition of MODERATE allows for the possibility of “large avalanches in isolated areas”. This is not a good time to go big in the backcountry.

A wild card right now are the glide cracks. One of these crevasse like features avalanched on Jan 4th for no obvious or apparent reason (see photo gallery). Glide cracks are like cornices in that they are very difficult to predict. We have not seen or had any reports of any more glide crack failures since Jan 4th, but it would still be wise to avoid traveling on, near, or underneath the path of any glide cracks.

Always remember that safe backcountry travel requires training and experience. You control your own risk by choosing where, when, and how you travel.

Thanks for checking today’s avalanche advisory. The next one will be posted tomorrow Wednesday January 20th.