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Issued
Thu, December 31st, 2009 - 7:00AM
Expires
Fri, January 1st, 2010 - 7:00AM
Forecaster
CNFAIC Staff
Avalanche risk The Bottom Line

Good morning backcountry travelers this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Thursday December 31st 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 North 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-

wx station went down at 9 am yesterday; so I will use Fresno Ridge down at Summit for a general idea of Turnagain Pass weather

3400′ –Fresno Ridge Wx Station-

Temps ranged between 25-26 degrees increasing by 1 degree since yesterday morning with calm to light winds averaging 1-11 mph from variable directions with a max gust of 17

2400′-Seattle Ridge Wx Station-

wx station went down yesterday 9 am yesterday, but we spent yesterday on Seattle Ridge working on this weather station and observed calm winds and mild temps

1800′-Center Ridge Wx Station-

Precip: 0.0 inches of water

Total depth of 60 inches after 1″ of settlement

Temperatures reached 31 degrees F yesterday and are currently the same as yesterday morning at 27 degrees F

Nowcast

Its hazy over Girdwood as of 5am but the moon is visible. The Middleton and the Kenai radars are mostly clear except for some light scattered precip. Most wx stations are not working this morning, but there does not appear to be any major weather happening right now.

Forecast

WESTERN PRINCE WILLIAM SOUND-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKST THU DEC 31 2009

.TODAY…MOSTLY CLOUDY WITH ISOLATED SNOW SHOWERS IN THE

MORNING…THEN MOSTLY SUNNY IN THE AFTERNOON. PATCHY FOG. HIGHS IN

THE MID 20S TO LOWER 30S. LIGHT WINDS EXCEPT WEST 10 TO 15 MPH NEAR

WHITTIER.

.TONIGHT…CLEAR. LOWS 15 TO 25…COLDEST INLAND. LIGHT WINDS EXCEPT

NORTH AND WEST 10 TO 20 MPH NEAR SEWARD AND WHITTIER.

.NEW YEARS DAY…MOSTLY SUNNY. HIGHS 15 TO 25. LIGHT WINDS EXCEPT

NORTH AND WEST 15 TO 25 MPH NEAR SEWARD AND WHITTIER.

TEMPERATURE / PRECIPITATION

SEWARD 33 22 22 / 20 0 0

GIRDWOOD 25 18 20 / 20 0 0

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

Sea-level: The QPF is calling for 0.0-0.05 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 14 and 23 degrees F with winds 5-10mph

AVALANCHE DISCUSSION

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

There are 4 main points of interest in the current snowpack

1.Stiffer snow and older wind slabs near ridgetops about 6 inches deep 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, snowboard, or snowmachine tracks on big open planer slopes. We mention this type of shallow instability because it could be a problem in very rocky terrain above cliffs on extreme terrain.

2.A weak layer of buried surface hoar about 10-12 inches deep is generally confined to elevations below 2000′. Some people have reported seeing it a bit higher up to 2400′, but most of it at lower elevations.

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 if big storm snow avalanches step down to these facets.

4.A new layer of surface hoar has formed on the surface. It has been observed at lower and mid elevations. This will be a potential new weak layer to watch after it gets buried.

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 NEXT YEAR on Friday January 1st. Happy New Year.

Thu, December 31st, 2009
Alpine
Above 2,500'
1 - Low
Avalanche risk
Treeline
1,000'-2,500'
1 - Low
Avalanche risk
Below Treeline
Below 1,000'
1 - Low
Avalanche risk
0 - No Rating
1 - Low
2 - Moderate
3 - Considerable
4 - High
5 - Extreme
Avalanche risk Avalanche risk Avalanche risk Avalanche risk Avalanche risk
Travel Advice Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern. Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding, and conservative decision-making essential. Very dangerous avalanche conditions. Travel in avalanche terrain not recommended. Extraordinarily dangerous avalanche conditions. Avoid all avalanche terrain.
Likelihood of Avalanches Natural and human-triggered avalanches unlikely. Natural avalanches unlikely; human-triggered avalanches possible. Natural avalanches possible; human-triggered avalanches likely. Natural avalanches likely; human-triggered avalanches very likely. Natural and human-triggered avalanches certain.
Avalanche Size and Distribution Small avalanches in isolated areas or extreme terrain. Small avalanches in specific areas; or large avalanches in isolated areas. Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas. Large avalanches in many areas; or very large avalanches in specific areas. Very large avalanches in many areas.
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This is 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.