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ARCHIVED - Forecasts expire after 24 hours.
Issued
Thu, February 12th, 2009 - 7:00AM
Expires
Fri, February 13th, 2009 - 7:00AM
Forecaster
CNFAIC Staff
Avalanche risk The Bottom Line

GENERAL ANNOUNCEMENTS

Good Morning backcountry travelers, this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Thursday, February 12, 2009 at 7am. This will serve as a general backcountry avalanche advisory issued 5 days a week Wednesday-Sunday for the Turnagain Arm area (Turnagain Pass is the core advisory area). Local variations always occur.

MOUNTAIN WEATHER ROUND UP

In the last 24 hours…

-General Weather Observations-

Temps have continued to increase at all weather stations from Summit to Girdwood by an additional 4-11 degrees. Winds at all ridgetop weather stations have backed off a little this morning, but were strong yesterday afternoon.

The DOT weather station near the crest the highway at Turnagain Pass at 1000 feet

Is recording a temp of 23 degrees (5 degrees warmer than yesterday) with calm winds.

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

Has a temp of 21 degrees (4 degrees warmer than yesterday). 0.2 inches of water and 2 inches of new snow has been recorded. Total snowpack depth is 66″.

The Sunburst weather station at 3800 feet in Turnagain Pass

Shows a temperature of 16 degrees (10 degrees warmer than yesterday). Winds have been moderate to strong averaging 7-34 mph out of the East with a max gust of 52 mph.

-Surface Analysis Maps-

Between 3am and 9pm yesterday, a weak low pressure moved into Prince William Sound and continued to get weaker (1000-1004mb). There is anCNFAIC Staff big storm building out in the Bering Sea (976-972mb).

-Radar-

Not much to report this morning. There is some moisture just outside of Prince William Sound. It must be the dregs of that low pressure from yesterday.

AVALANCHE HAZARDS

Primary avalanche concerns

-Surface wind slabs on slippery bed surface on alpine ridges above 3000 feet

Secondary avalanche concerns

-Rain crust from January hurricane below 3000 feet.

AVALANCHE AND SNOWPACK

Bottom Line

Extra Caution is advised today. Avalanche hazards have increased since yesterday due to strong wind and some new snow. There will be pockets of considerable avalanche hazard. These are the types of conditions when most people get caught in avalanches because human overconfidence in the snow pack collides with deeper slabs.

Discussion

We received anCNFAIC Staff report of a human-triggered avalanche from Girdwood Valley yesterday. Add that to the list in the general snow conditions at the bottom of the page, and you will see that people have been frequently triggering avalanches in: Girdwood Valley, Virgin Creek, Kern Creek, Placer River Valley, and Turnagain Pass. Our entire advisory area for the Turnagain Arm area has been having problems with human-triggered avalanches on that slippery wind hammered layer above 3000 feet, and on the rain crust below 3000 feet to sea-level.

*Yesterday’s strong wind and new snow have increased the chance of triggering larger, more destructive, and potentially deadly avalanches.*

Safe terrain management is essential today.

WEATHER FORECAST

WESTERN PRINCE WILLIAM SOUND-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKST THU FEB 12 2009

…STRONG WIND EARLY FRIDAY MORNING THROUGH FRIDAY AFTERNOON

THROUGH PORTAGE VALLEY AND TURNAGAIN ARM…

.TODAY…PERIODS OF SNOW…ESPECIALLY ALONG THE SOUND. SNOW

ACCUMULATION UP TO 2 INCHES. HIGHS IN THE MID 20S TO LOWER 30S.

LIGHT WINDS. NEAR SEWARD…NORTH WIND 15 TO 30 MPH BECOMING

LIGHT IN THE AFTERNOON.

.TONIGHT…SNOW SHOWERS LIKELY…ESPECIALLY ALONG THE SOUND. SNOW

ACCUMULATION UP TO 2 INCHES. LOWS IN THE LOWER 20S TO LOWER 30S.

EAST WIND 10 TO 15 MPH. THROUGH PORTAGE VALLEY AND TURNAGAIN

ARM…SOUTHEAST WIND 15 TO 25 MPH INCREASING TO 25 TO 40 MPH

AFTER MIDNIGHT.

.FRIDAY…SNOW SHOWERS LIKELY. SNOW ACCUMULATION 1 TO 5 INCHES.

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

35 TO 50 MPH THROUGH PORTAGE VALLEY AND TURNAGAIN ARM.

TEMPERATURE / PRECIPITATION

SEWARD 28 27 36 / 40 40 60

GIRDWOOD 26 26 32 / 80 60 60

This concludes today’s avalanche advisory the next advisory will be on Friday, February 13th (ooga booga). Thanks and have a great day.

Thu, February 12th, 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. 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.