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ARCHIVED - Forecasts expire after 24 hours.
Issued
Wed, February 11th, 2009 - 7:00AM
Expires
Thu, February 12th, 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 Wednesday, February 11, 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-

The weather is changing. Temps have increased by 8-20 degrees at all weather stations from Summit to Girdwood this morning. Winds have also been increasing at all ridgtop weather stations. This change in weather jives with the NOAA forecast which is calling for a little snow.

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

Is recording a temp of 18 degrees (14 degrees warmer than yesterday) with calm winds.

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

Has a temp of 17 degrees (13 degrees warmer than yesterday). 0.1 inches of water and 1 inch of new snow has been recorded. Total snowpack depth is 65″.

The Sunburst weather station at 3800 feet in Turnagain Pass

Shows a temperature of 6 degrees (8 degrees warmer than yesterday). Winds have been light to moderate averaging 2-20 mph out of the ESE with a max gust of 28 mph.

-Surface Analysis Maps-

There is a medium sized storm out in the Bering Sea that is getting weaker (969-978mb). Its one of those deals where the center of this storm is far away from us, but its outer arm is pulling warm moisture up toward us.

-Radar-

There is no green monster out there ready to dump tons of snow on us, but there is some stuff happening nearby. Most of the moisture appears to still be over King Salmon, but there is a blue haze building into pockets of green moving NW toward Seward, Prince William Sound, and the Cook Inlet.

AVALANCHE HAZARDS

Primary avalanche concerns

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

Secondary avalanche concerns

-Rain crust (ice layer) from January hurricane below 3000 feet.

AVALANCHE AND SNOWPACK

Bottom Line

Elevated Caution is still advised today. We continue to get reports of small human-triggered avalanches 5-12 inches deep in: Turnagain Pass, Placer River Drainage and Girdwood Valley. These avalanches have had minor consequences lately, but might become VERY dangerous after we get more wind or snow.

Discussion

Right now, this instability is not too big of a deal if you manage your terrain and stick to clean runs away from terrain traps like gullies. We did get a report of a skier triggering one of these small slabs on Magnum on Sunday and getting dragged over some rocks, but skied out with no injuries. We also got reports of more small slabs in Placer River, Kern Creek and Virgin Creek.

If the surface snow continues having a difficult time bonding to those slippery surfaces today, then how do you think they will respond to the next dump of snow? That’s the big question in my head. I guess it will depend on how the next storms roll in. The current storm does not look like it will pack too much of a punch, but we should be careful with fresh windslabs. It seems like if we get a couple inches here and a couple inches there, then these slippery weak layers will sneak up on us and result with a bad combination of human overconfidence in the snowpack and the tipping point on the avalanche scale.

We continue to look at those slippery crusts. One of my main concerns for the future are the bowls along Seattle Ridge. There is a rain crust sandwich that continues to grow facets above and below the crust. We went into Main Bowl again yesterday. This is where we dig most of our pits on the motorized side so that we can keep a baseline and look for trends that will generally represent the conditions in the CNFAIC Staff bowls.

The reason why I am so concerned with this layer is that it is located at a bad elevation for the starting zones in the bowls along Seattle Ridge. Crusts are responsible for lots of avalanche accidents after they get buried with enough snow. Right now, this rain crust shows good-moderate stability above the crust, but could become a problem after there is a deeper slab on top. I know there are tracks everywhere, but those tracks might not make a difference on that rain crust after it gets buried. I think we should be very cautious over there if we ever get about 3 feet of snow on top of that weak layer.

WEATHER FORECAST

WESTERN PRINCE WILLIAM SOUND-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKST WED FEB 11 2009

.TODAY…SNOW. SNOW ACCUMULATION 2 TO 3 INCHES. HIGHS IN THE 20S.

EAST WIND 10 TO 15 MPH. GUSTS TO 30 MPH ALONG TURNAGAIN ARM DURING

THE MORNING.

.TONIGHT…SNOW. SNOW ACCUMULATION 2 TO 4 INCHES. LOWS 15 TO 25.

NORTH WIND 10 TO 15 MPH EXCEPT NORTH 20 TO 30 MPH NEAR SEWARD.

.THURSDAY…NUMEROUS SNOW SHOWERS. SNOW ACCUMULATION UP TO

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

NEAR SEWARD…NORTH WIND 25 MPH DECREASING TO 10 MPH IN THE

AFTERNOON.

TEMPERATURE / PRECIPITATION

SEWARD 27 21 31 / 80 80 60

GIRDWOOD 21 16 29 / 60 60 40

This concludes today’s avalanche advisory the next advisory will be on Thursday, February 12th. Thanks and have a great day.

Wed, February 11th, 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.
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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.