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ARCHIVED - Forecasts expire after 24 hours.
Issued
Thu, January 29th, 2009 - 7:00AM
Expires
Fri, January 30th, 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, January 29, 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-

Temperatures have increased 6-9 degrees at all weather stations. Ridge top winds have been light to moderate averaging 8-17 mph with a few strong gusts up to 27 mph. A dusting to an inch or two of new snow fell yesterday.

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

Is recording a temp of 25 degrees (8 degrees warmer than yesterday), calm winds averaging 4mph and the same total snowpack depth of 41 inches (same as yesterday).

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

Has a temp of 26 degrees (9 degrees warmer than yesterday). It looks like 1 inch of new snow fell but zero water was recorded. Total snowpack depth is 61 inches.

The Friends of the Avy Center Sunburst weather station at 3800 feet in Turnagain Pass

Is recording a temperature is 20 degrees F (9 degrees warmer than yesterday). Winds have been light to moderate averaging 8-17 mph with a strong gust of 27 mph.

-Surface Analysis Maps-

From 3 am Wednesday to 9pm last night…

Show that same weak storm (992) from yesterday that was over the Aluetians moving NE towards us. It looks like we are on its outer arm.

-Jet Stream-

The analysis from 9pm last night shows the main flow of the jet stream moving west to east over the top of us and to our south. In the next 48 hours, it is forecasted to shift to our south moving west to east pointing at BC and Washington.

-Satellite-

Shows that the firehose is still pointed at SE AK.

-Radar-

The Middleton radar shows moderate amounts of green precip inside Prince William Sound. The Kenai radar shows some moderate green precip over Cook Inlet.

AVALANCHE THREATS

Primary avalanche concerns

-Deep slabs 2-6 feet thick on top of January facets

Secondary avalanche concerns

-Glide Cracks (now they are bridged over, don’t fall in)

WATCH OUT SITUATIONS

-New surface wind slabs on top of those slippery crusts

-Slopes that do not have a clean run out

AVALANCHE AND SNOWPACK DISCUSSION

Normal caution is advised. The January 14-16 storm, “The Hurricane”, left behind slabs about 2-6 feet deep on top of a weak layer of facets that formed in early January. Rain and wet snow saturated the top 1-2 feet of the snowpack up to elevations of about 2800 feet leaving behind a thick rain crust. Above 2800 feet, the wind really hammered the snow up to the ridges leaving behind a smooth wind crust. Those deep slabs continue to be our main concern today, even though it is unlikely to trigger that weak layer. The next big avalanche concern will be new snow on top of those slippery crusts.

That weak layer of January facets has NOT been reactive to human triggers.

We are still finding those facets just about everywhere that we dig. Almost every stability test shows that it is very difficult to get that weak layer to fail, and when it does it is very low quality Q2-Q3. Stability tests show good stability on this weak layer.

Those facets WERE reactive to natural triggers during that last big storm.

We continue to find and get reports that more avalanches ripped out during that January 14-16 storm. Most of them avalanched below 3000 feet where the storm snow was heavy. Elevations above 3000 feet remained cold and dry; so, those January facets are still very sugary at higher elevations.

The avalanche hazard is low right now below 3000 feet, even though the text books say a slab on top of facets is a terrible combination for avalanches. There are still some question marks and pockets of elevated caution above 3000 feet. The weak layer of January facets might become a bigger concern during next large storm, especially if warm temps or rain make it above 3000 feet.

NOAA is not forecasting any drastic changes today (see forecast below).

I keep mentioning the glide cracks as a secondary concern mostly because they are now bridged over and are now more difficult to see. They could be a dangerous place to fall, like falling into a glacier crevasse. Be careful on the south side of Magnum where we have seen several glide cracks. Plus, I don’t really understand glide cracks. They seem to want to avalanche a different times for different reasons; so, I always treat them like cornices and try to avoid them. I don’t think we’ve seen the last of those things this year.

WEATHER FORECAST

WESTERN PRINCE WILLIAM SOUND-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKST THU JAN 29 2009

.TODAY…SNOW SHOWERS. SNOW ACCUMULATIONS 2 TO 4 INCHES. HIGHS IN THE

UPPER 20S TO MID 30S. SOUTH TO EAST WINDS 10 TO 20 MPH.

.TONIGHT…SNOW. SNOW ACCUMULATION 1 TO 3 INCHES. AREAS OF BLOWING

SNOW AFTER MIDNIGHT NEAR SEWARD AND WHITTIER. LOWS IN THE UPPER TEENS

TO MID 20S. LIGHT WINDS. NEAR SEWARD…LIGHT WINDS BECOMING NORTH TO

WEST 10 TO 20 MPH.

.FRIDAY…SNOW LIKELY IN THE MORNING…THEN A CHANCE OF SNOW IN

THE AFTERNOON. SNOW ACCUMULATION UP TO 1 INCH. HIGHS IN THE UPPER

TEENS TO MID 20S. NORTH TO WEST WINDS 15 MPH. SEWARD AND

WHITTIER…NORTH TO WEST WINDS 20 TO 30 MPH. AREAS OF BLOWING SNOW

REDUCING VISIBILITIES TO ONE HALF MILE AT TIMES.

TEMPERATURE / PRECIPITATION

SEWARD 32 22 25 / 80 60 40

GIRDWOOD 30 18 22 / 100 80 60

Thanks for checking the CNFAIC avalanche advisory. Have a great day.

Thu, January 29th, 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.