Turnagain Pass

Good morning backcountry travelers this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Wednesday December 30th 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

All areas designated for snowmachines on the Chugach National Forest are open to snowmachines except Placer and 20 Mile. Please remember that Center and Divide Creeks near the Johnson Pass Trailhead are always closed due to the current Forest Plan.

WEATHER ROUNDUP

Will recent weather effect avalanche conditions today?

Well, let’s take a closer look at the precip, winds, and temps.

Hindcast (Last 24 hours)

3800′ -Sunburst Wx Station-

Temperatures have decreased from 27 to 24 degrees F with light winds averaging 6-15 mph from the ESE with a moderate max gust of 22 mph

2400′-Seattle Ridge Wx Station-

Winds have been light averaging 8-17 mph from ESE with a moderate max gust of 23 mph

1800′-Center Ridge Wx Station-

Precip: 0.0 inches of water

Total depth of 61 inches after 1″ of settlement

Temperatures have decreased from 31-27 degrees F

Nowcast

Its clear over Girdwood as of 5am. The Middleton radar shows a very small band of precip pretty far out in the Gulf of AK and the Kenai radar is clear. Compared to yesterday morning, temps are colder at all wx stations this morning by 2-4 degrees. Temps range from 26 at sea level to 24 at 3800′. Winds are calm to light at all ridgetop wx stations.

Forecast

WESTERN PRINCE WILLIAM SOUND-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKST WED DEC 30 2009

.TODAY…MOSTLY CLOUDY. PATCHY FOG. SCATTERED SNOW SHOWERS IN THE

AFTERNOON. HIGHS IN THE LOWER 20S TO MID 30S…COLDEST INLAND. LIGHT

WINDS.

.TONIGHT…MOSTLY CLOUDY. ISOLATED SNOW SHOWERS IN THE EVENING.

LOWS 15 TO 25. LIGHT WINDS.

.THURSDAY…PARTLY CLOUDY IN THE MORNING THEN BECOMING MOSTLY

SUNNY. HIGHS IN THE LOWER 20S TO LOWER 30S. LIGHT WINDS EXCEPT

WEST 10 TO 15 MPH NEAR WHITTIER.

TEMPERATURE / PRECIPITATION

SEWARD 34 23 27 / 30 20 0

GIRDWOOD 23 21 25 / 0 0 0

Short Term Weather Models (NAM, WRF, QPF) for the Kenai Mountains near Turnagain Pass

Sea-level: The QPF is calling for 0.0-0.1 inches of water forecasted today, but the WRF is calling for 0.0 precip over Turnagain Pass.

3000′: temps forecasted between 23 and 32 degrees F with winds 0-5mph

6000′: temps forecasted between 23 and 32 degrees F with winds 5-10mph

AVALANCHE DISCUSSION

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

Sunburst has been the subject of the Avalanche Center’s most recent snow study. Between Saturday 12/26/2009 and Monday 12/28/2009 there were 20 different compression tests and 1 extended column test at multiple elevations at 1500′, 2000′, 2500′, 3000′, and 3500′. Sometimes it’s good to focus on one mountain to try to find any patterns and combine the results from CNFAIC Staff nearby locations for a good general impression of snowpack over a larger area. Our main area of interest has been how the snow changes through different elevations. Similar observations were reported recently from Magnum and Center Ridge.

There are three main points of interest in the current snowpack

1.The buried surface hoar is generally confined to elevations below 2000′. Some people have reported seeing it a bit higher up to 2400′, but most of it is lower. Depending on location this buried surface hoar has been observed buried about 10-12 inches deep.

2.Old wind slabs near ridgetops that are about 6 inches deep near the surface still failed easily in compression tests on 12/28/2009 with scores as low as CTE2Q2@15cm. This stiffer snow did not appear reactive to ski or snowboard tracks.

3.The facets on the ground are strangely starting to show slightly decreased stability since last week. These facets are generally rounding out, but have shown moderate failures with test scores as low as CTM13Q3@70cm. They show more activity where the snowpack is less than 3 feet deep, but were reactive as of Monday 12/28/09 in a 5 foot deep isolated column. I’m not super concerned with these facets, but it does raise a few eyebrows. This data jives with a recent report where somebody observed some small slabs stepping down to the ground on steep terrain at about 1800′. Maybe these facets will show themselves during the next big pineapple express.

These 3 points of interest are not overly concerning for today’s avalanche danger. Due to a lack of significant weak layers and a mild weather forecast, the avalanche danger for Turnagain Pass will remain at LOW today. LOW is defined as: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. Natural and human-triggered avalanches unlikely. Small avalanches in isolated areas or extreme terrain.

AnCNFAIC Staff concern today will be the glide cracks. A couple of large glide cracks have opened north of the snowmachine uptrack to Seattle ridge. Odds are there are numerous more of these crevasse like features which may be difficult to see. People and dogs have fallen into these cracks before, and they can be very difficult to get out of. Sometimes these glide cracks will avalanche, but this does not appear to be a concern today. It’s always a good idea to treat glide cracks like cornices and avoid traveling underneath their path. Like cornices, glide cracks are very difficult to predict.

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 Thursday December 31st.