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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sat, December 6th, 2008 - 7:00AM
Expires
Sun, December 7th, 2008 - 7:00AM
Forecaster
CNFAIC Staff
Avalanche risk The Bottom Line

GENERAL ANNOUNCEMENTS

Good morning backcountry travelers, this is Carl Skustad with the Chugach National Forest Avalanche Information Center on Saturday, December 6, 2008 at 7am. This will serve as a general backcountry avalanche advisory issued for the Turnagain Arm. Local variations always occur. Note: We are now issuing regular advisories 5 days a week Wednesday-Sunday.

INTERAGENCY AVALANCHE RESCUE TRAINING

On the weekend of December 13-14, there will be an avalanche rescue training taking place at Turnagain Pass. Please be aware of rescue workers, helicopters, and areas set up for rescue training drills.

MOUNTAIN WEATHER ROUND UP

In the last 24 hours…

-The Center Ridge weather station at 1800 feet in Turnagain Pass-

No new snow recorded. Current temperature is 33 degrees F (no change from yesterday morning). Total snowpack depth is 46 inches, that’s down 2 inches.

-Sunburst weather station at 3800 feet in Turnagain Pass-

This station will be giving us trouble until we get a new battery up to this remote site. No current data!

-Max’s weather station at 3200 feet in Girdwood Valley-

31 deg F with SE winds in the mid teens with gusts to 25.

-Surface Analysis Maps-

Shows two low pressure systems (994 and a 990 mb) spinning up the Aleutian chain.

-Radar-

The Middleton radar shows a wall of light to moderate precip over Prince William Sound heading NNE toward Valdez and Cordova. The Kenai radar shows a wall of light to moderate precip over Kenai.

-General Weather Observations-

All the temperatures are up again this morning. Most areas are above the freezing point. The weather challenge today will be if precip falls as rain or snow. Our snow line is up to approximately 1800 feet.

Also, a huge thanks to Skip and Crane for building this web site out. These guys deserve all the credit behind the sick weather graphs, maps, and cool functionality of this web site. They are two of many friends group members that make this Avi Center possible.

PRIMARY AVALANCHE CONCERNS

-Possible rain on snow

-Wind slabs of deeper dense snow on top of shallow weaker less dense snow

-buried surface hoar (about 3 feet deep)

-Rapid loading of any kind (precip, wind, temperature)

AVALANCHE AND SNOWPACK DISCUSSION

AnCNFAIC Staff warm day in store today for the advisory area. Expect soggy conditions up to the 1800 ft freeze line. I don’t see a whole lot of precipitation today but the take home this morning is “rain on new snow, get away”. If the freeze line rises even more and you notice rain on new snow, the avalanche hazard will rise quickly. If this does occur there would be a chance for natural and human triggered avalanche activity. I think this avi activity is possible, but restricted to an elevational band from 1800 to 2500 feet. Below this elevation our snowpack is pretty damp and has been for over 48 hours.

Above this elevational band normal caution is advised. Thursday, Matt and I climbed up the Sunnyside (top of Seattle Ridge) of T-Pass to investigate a week old avalanche the snowmachineres triggered last Friday. As we suspected this large avalanche failed on top of the weak faceted October snow near the ground. We continue to get fairly stable test results in our alpine snow pits (CT30+Q2101cm) but we can’t trust these tests 100%. What they do tell us is that these layers are on the mend. In most places we will not have enough of an impact with our snowboard, snow-machine , or ski, to trigger an avalanche. Places to still wake the avalanche dragon exist near areas of thinner snow like rock bands, alder clumps, and scoured ridges.

The bottom line is we have a 3-6 foot dense slab on top of weaker unconsolidated snow in most alpine locations. We have not received enough snow or water load to trigger these slabs. Each storm pushes us closer to the trigger point. This point is reached when the stress of the snowpack exceeds the strength of the weak layer. Any sudden change in weather will increase the avalanche hazard quickly. Wind, snow, or more importantly today rain could be enough stress on the snowpack.

WESTERN PRINCE WILLIAM SOUND-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKST SAT DEC 6 2008

.TODAY…RAIN AND SNOW SHOWERS. SNOW ACCUMULATION UP TO 1 INCH

INLAND. HIGHS IN THE 30S. LIGHT WINDS.

.TONIGHT…SNOW AND RAIN. SNOW ACCUMULATION UP TO 1 INCH. LOWS IN

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

.SUNDAY…SNOW AND RAIN LIKELY IN THE MORNING…THEN RAIN LIKELY

IN THE AFTERNOON. NO SNOW ACCUMULATION. HIGHS IN THE 30S. LIGHT

WINDS.

.SUNDAY NIGHT…MOSTLY CLOUDY WITH SCATTERED SNOW SHOWERS. LOWS

IN THE MID 20S TO LOWER 30S. VARIABLE WIND TO 10 MPH.

.MONDAY…CLOUDY WITH A CHANCE OF SNOW. HIGHS IN THE MID 20S TO

LOWER 30S. NORTHEAST WIND 10 TO 20 MPH EXCEPT NORTH 30 MPH NEAR

SEWARD.

TEMPERATURE / PRECIPITATION

SEWARD 38 32 36 / 80 80 60

GIRDWOOD 35 28 34 / 80 40 60

This concludes todays advisory, the next advisory will be on Sunday the 7th, thanks and have a great day!

Sat, December 6th, 2008
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.
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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.