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ARCHIVED - Forecasts expire after 24 hours.
Issued
Thu, December 25th, 2008 - 7:00AM
Expires
Fri, December 26th, 2008 - 7:00AM
Forecaster
CNFAIC Staff
Avalanche risk The Bottom Line

GENERAL ANNOUNCEMENTS

Happy Holidays backcountry travelers, this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Thursday, December 25, 2008 at 7am. This will serve as a general backcountry avalanche advisory issued for the Turnagain Arm (Turnagain Pass is the core advisory area). Local variations always occur. Note: We issue advisories 5 days a week Wednesday-Sunday.

MOUNTAIN WEATHER ROUND UP

In the last 24 hours…

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

No Data. This weather station is down; so, let’s look at similar location at Grandview.

-The Grandview weather station at 1100 feet along the railroad tracks-

Recorded 0 inches of water or new snow. Current temp is 14 degrees F (7 degrees colder than yesterday)

-Sunburst weather station at 3800 feet in Turnagain Pass-

Recorded light winds averaging 1-14 mph from the northwest with a strong gust of 28 mph. Current temperature is 11 degrees F (same as yesterday)

-Surface Analysis Maps-

From 3 am Wednesday to 9pm last night…

Show a new storm moving west over the Bering Sea in our direction. Its not super big, but it is building (1000Mb-991Mb)

-Jet Stream-

The analysis from 9pm last night showed it flowing out of the Bering Sea right over the top of us. It is forecasted move to our south and point the firehose at Washington and Oregon.

-Satellite-

As of 6:00 am this morning…shows precip moving very fast over the top of us.

-Radar-

The Middleton radar shows a wall of precip south of Seward into the Gulf of Alaska moving east.

The Kenai radar shows a big blob of green precip heading towards Homer.

-General Weather Observations-

Compared to yesterday…Temps are colder at sea level by 12-17 degrees F, and ridgetop temps stayed the same or got slightly warmer. Winds have been light to moderat, and there are some strong gusts.

PRIMARY AVALANCHE CONCERNS

-October Facets on the ground

-Crust (about 3.5 feet deep) with Buried Surface Hoar on Top (found at elevations below 2500 feet)

-latest surface hoar near top of snow pack

SECONDARY AVALANCHE CONCERNS

-Glide Cracks (see photos)

-Wind slabs

WATCH OUT SITUATIONS

-New storm snow

-Rocky terrain with shallow snow connected to deeper snow (photo gallery)

-Steep rollovers (photo gallery)

-If you hear any “whumpfing” or feel any collapsing, then get to safe terrain immediately and call it a day.

-Glide cracks bridged over.

AVALANCHE AND SNOWPACK DISCUSSION

We got a report of a small human-triggered avalanche yesterday on the southern aspect of Cornbiscuit (Thanks Dan). The skier described what sounds like a glide crack that was bridged over with a wind deposited snow. He was carried 200 feet before “swimming” out of the “slow moving” and “soft” debris. We also had CNFAIC Staff reports of small wind slabs around the area.

Terrain management is the key to safety with our existing snowpack. Early season snowpacks like what we have right now are not ready for the big lines that Alaska is famous for. We all need to keep our human factors in check and stick to planar slopes with clean runouts, and avoid steep or complex terrain.

Although the loose sugary faceted snow that formed on the ground in October is showing signs of improved stability, it still is our biggest concern for avalanches. Every snowpit this season shows that our entire snowpack is a consolidated slab on top of a weak layer of facets. Most of our stability tests show good stability right now. However, snow pits do not tell the whole story. Since a new storm is heading our way, I think it is a good idea to talk out load about what has been going on.

The weak layer of October facets failed during the last big storm (12/8/08) and resulted in large avalanches that propogated across very wide areas. This weak layer also failed with human-triggers 5 days after that storm near rocky and complex terrain near steep rollovers. These human-triggered avalanches where small relative to the entire slope and did not propogate very wide. They stayed isolated to specific terrain features, but these were very dangerous for people.

If we get hit hard by this next storm, the avalanche hazard could increase and become very dangerous. My level of uncertainty is very high with what the next big storm will do; so, I’m not going to take any chances. I’m not really sure if this next storm will be that big, but it could still create a drastic change to the existing snowpack. There is also a mystery layer of buried surface hoar near the surface. We saw it forming mostly at mid elevations up to 2800 feet, but it got buried under 1-2 inches of snow and became very difficult to track; so, there is anCNFAIC Staff big question mark for me.

Stability has been very good lately, but we all need to be careful with the next rapid change.

WEATHER FORECAST

WESTERN PRINCE WILLIAM SOUND-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKST THU DEC 25 2008

…STRONG WIND LATE TONIGHT THROUGH FRIDAY AFTERNOON NEAR

SEWARD AND WHITTIER…

.TODAY…SNOW DEVELOPING THIS MORNING. SNOW ACCUMULATION 2 TO 4

INCHES. BLOWING SNOW THROUGH PORTAGE VALLEY AND TURNAGAIN ARM

WILL REDUCE VISIBILITY TO ONE HALF MILE AT TIMES THIS AFTERNOON.

HIGHS IN THE MID TEENS TO LOWER 30S. NORTH TO EAST WIND 10 TO 20 MPH

EXCEPT EAST WIND INCREASING TO 25 TO 35 MPH THROUGH PORTAGE VALLEY

AND TURNAGAIN ARM.

.TONIGHT…SNOW. SNOW ACCUMULATION 3 TO 7 INCHES. LOWS 5 TO 25

ABOVE…COOLEST INLAND. NORTH TO EAST WIND 10 TO 20 MPH BECOMING

NORTH TO WEST 15 TO 30 MPH WITH GUSTS TO 45 MPH NEAR SEWARD AND

WHITTIER. THROUGH PORTAGE VALLEY AND TURNAGAIN ARM…EAST WIND

25 TO 35 MPH DIMINISHING DURING THE EVENING THEN SHIFTING TO WEST

AFTER MIDNIGHT.

TEMPERATURE / PRECIPITATION

SEWARD 27 24 24 / 100 100 40

GIRDWOOD 24 18 22 / 100 100 60

Thu, December 25th, 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. 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.
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.