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Issued
Sun, December 13th, 2009 - 7:00AM
Expires
Mon, December 14th, 2009 - 7:00AM
Forecaster
CNFAIC Staff
Avalanche risk The Bottom Line

Good morning backcountry travelers this is Lisa Portune with the Chugach National Forest Avalanche Information Center on Sunday, December 13 at 7 am. This will serve as a general backcountry avalanche advisory issued for Turnagain Arm with Turnagain Pass as the core advisory area (advisory does not apply to highways, railroads, or operating ski areas).

ANNOUNCEMENTS

All areas designated for snowmachines (except Placer and 20 Mile) on the Chugach National Forest are open. Please remember that Center and Divide Creek near the Johnson Pass Trailhead are always closed due to the current Forest Plan. We are monitoring the snow at Placer and 20 Mile and will open those areas as soon as there is enough snow.

WEATHER ROUNDUP

It’s been a pretty mellow week weather-wise with more than our share of smCNFAIC Staffing fog. Well at least the temperatures have been exciting with this crazy inversion. Hopefully you had a chance to climb above the fog and enjoy the sunshine and balmy temperatures up high. Our last significant snowfall was 12 days ago on Tuesday December 1st. Yesterday ridgetop winds were light and variable at all weather stations. Mountain temperatures above 3000 feet climbed to the mid to upper 30’s while sea level temperatures remained in the single digits.

As of 4 am this morning, ridgetop winds remain light and variable at all locations. Skies are clear in Girdwood. Temperatures currently range from 9F at sea level to 29F at 3800 feet. We will finally begin to see the inversion break this afternoon from increased northwest flow as an arctic low moves southward. Temperatures will warm up at sea level and cool off at the higher elevations. Expect continued light winds today, mountain temperatures in the low 20’s, and mostly cloudy skies by afternoon. There’s a good chance of snow tomorrow although the actual amounts are still up in the air. We’ll keep our fingers crossed.

-The Center Ridge Wx Station at 1800 feet/Turnagain Pass-

recorded no new snow yesterday and temps in the low 20’s. The current temp is 24F (3 degrees warmer than yesterday) with a total snowpack depth of 55 inches (0 inches of settlement since yesterday)

-The Sunburst Wx Station at 3800 feet/Turnagain Pass-

recorded light westerly winds yesterday with temps ranging from 29-36F. The current temp is 29F (same as yesterday).

-The Summit Lake Wx Station at 1200 feet-

recorded no new snow yesterday and temps ranging from 5-13F. The current temp is 14F (9 degrees warmer than yesterday) with a total snowpack depth of 25 inches (same as yesterday).

-The Fresno Ridge Wx Station at 3400 feet/Summit Lake-

recorded light and variable winds yesterday with temps ranging from 26-33F. The current temp is 25F (2 degrees colder than yesterday).

The weather forecast for:

WESTERN PRINCE WILLIAM SOUND-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKST SUN DEC 13 2009

.TODAY…MOSTLY CLOUDY. PATCHY MORNING FOG. A SLIGHT CHANCE OF

SNOW ALONG THE COAST IN THE AFTERNOON. HIGHS IN THE TEENS TO

LOWER 20S INLAND AND MID TO UPPER 20S ALONG THE COAST. LIGHT WINDS.

.TONIGHT…MOSTLY CLOUDY WITH A CHANCE OF SNOW. LOWS 5 TO 15 ABOVE

EXCEPT IN THE LOWER TO MID 20S ALONG THE COAST. LIGHT WINDS.

.MONDAY…SNOW LIKELY. SNOW ACCUMULATION 1 TO 4 INCHES. HIGHS

IN THE MID 20S TO LOWER 30S. LIGHT WINDS.

.MONDAY NIGHT…SNOW LIKELY. LOWS IN THE 20S. VARIABLE WIND

TO 10 MPH.

.TUESDAY…SNOW LIKELY. HIGHS IN THE MID 20S TO LOWER 30S.

VARIABLE WIND TO 10 MPH.

TEMPERATURE / PRECIPITATION

SEWARD 26 22 30 / 0 30 40

GIRDWOOD 18 14 28 / 0 20 60

AVALANCHE DISCUSSION

Today, a LOW avalanche danger exists on all slopes which means that natural and human-triggered avalanches are unlikely. We are looking at generally stable avalanche conditions, but as always, watch for unstable snow on isolated terrain features. Evaluate the snow and terrain carefully and always use good travel habits.

It has been 11 days since our last reported avalanche at Turnagain Pass, and the snowpack is showing no obvious signs of instability. Folks are skiing, riding, and highmarking steep slopes without incident. Snow conditions vary from 4-6 inches of dry faceted powder and surface hoar below treeline to supportable windslab, smooth chalky windscour, punchy breakable crust, and windbuffed powder at the higher elevations. Despite the lack of snow and wind, our snowpack continues to evolve and change due to the air temperatures. The next weak link in our snowpack is the current snow surface, especially at the mid to lower elevations where recently formed surface hoar and dry faceted powder is sitting on a variety of firm bed surfaces. Monster-sized feathery crystals up to 1 inch in size have been observed up to 1600 feet elevation. Smaller surface hoar crystals up to ΒΌ inch in size exist up to 2400 feet elevation. Once buried with enough snow, we’ll probably see some action on this layer. Also, numerous glide cracks were reported in the north facing trees on Tincan. Be careful not to fall into one of these crevasse-like openings.

A special note for Summit Lake travelers: Several small to medium sized natural avalanches ripping out to the ground were reported this past week, although the exact dates are unclear. A thinner snowpack and warm temps up high may be responsible for this. We took a look from the road yesterday and noticed the fracture lines on these slides were blown in with snow, indicating they happened before or during last weekend’s (12/5 and 12/6) strong winds.

If you get out in the backcountry give us a call at 754-2369 or send us your observations using the button at the top of this page. I will issue the next advisory tomorrow morning at 7am.

Sun, December 13th, 2009
Alpine
Above 2,500'
0 - No Rating
Avalanche risk
Treeline
1,000'-2,500'
0 - No Rating
Avalanche risk
Below Treeline
Below 1,000'
0 - No Rating
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. Dangerous avalanche conditions. 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.
Observations
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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.