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Issued
Thu, February 10th, 2011 - 7:00AM
Expires
Fri, February 11th, 2011 - 7:00AM
Forecaster
Kevin Wright
Avalanche risk The Bottom Line

Good morning backcountry travelers this is Kevin Wright with the Chugach National Forest Avalanche Information Center on Thursday, February 10th at 7am. This will serve as 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).

BOTTOM LINE

The avalanche hazard rating is MODERATE with pockets of CONSIDERABLE. New storm snow and wind slab from the recent storm are the most likely concern to find. The older deeper layers are still prevalent and harder to trigger but potentially more dangerous than the new storm snow.

AVALANCHE DISCUSSION

We just got through anCNFAIC Staff small storm. New snow adds stress to an already weak structure and high wind piled that new snow (and the stress) onto lee aspects. A couple new avalanches were seen yesterday but overall not much to speak of. Total precipitation was only a few inches in Turnagain Pass, closer to 1 foot in Girdwood.

Recent skier and snowmachine triggered avalanches prove that our weak layers are not finished giving us problems. The avalanche off the south face of Magnum on Monday was the perfect example of the kind of avalanche and terrain we’re concerned about right now in Turnagain Pass. Steep and rocky terrain allows a person’s weight to affect the deeper weak layers from the shallow trigger points. New snow and wind will aggravate the problems and make it harder to identify relative depth around rocky complex terrain.

The old weak layers are still showing signs that they can be triggered with the effect of a backcountry traveler. The storm over the last couple days won’t be enough to produce widespread activity on its own. With an already weak structure underneath and a little more added weight from the recent storm, it raises the concern above an already elevated baseline. The old weak layers may fail with each additional load until we have a truly significant storm that doesn’t produce avalanches on these layers. So far none of our recent storms have been anywhere near large enough.

If you haven’t noticed already, this winter is providing the perfect recipe for old weak layers to stick around and haunt us for the long term. Clear and cold weather combined with a shallow snowpack in December formed the facets. Now our storms are giving us just enough snow to stress the weak layers close to the breaking point, but not enough to cause widespread natural avalanches and actually clean out the instabilities. This leaves us with mostly intact weak layers. Every time we get a little new snow it adds stress and makes it likely for human triggered avalanches to happen.

Primary concern: Deep persistent instabilities. These are less likely than the new wind slab to be triggered but far more dangerous right now.

Secondary concern: recent wind slab. The strong winds over the last few days combined with a few inches of new snow have created wind slabs in lee aspects.

Encyclopedia of avalanche terms.

WEATHER ROUNDUP

The storm ended yesterday in Turnagain Arm. Girdwood got 10+ inches at upper elevations. Turnagain pass only got 2-3 inches. The storm came in with more blowing than snowing. Wind speeds reached 78mph on Sunburst ridge. Through the region the wind effect is obvious from a distance. Rain line briefly hit up to 1000 feet. More rain and snow showers are possible today with some strong wind.

ANNOUNCEMENTS

Backcountry film festival tonight at APU Grant Hall theatre at 7:00pm.

All proceeds benefit the Alaska Avalanche School. See the event calendar for more details.

The Friends of the CNFAIC (FCNFAIC) needs your thoughts! With a new staff of forecasters and a list of previously completed goals, the program is growing and potentially heading in new directions. The FCNFAIC wants to know what you have to say about YOUR avalanche center, so please complete the following anonymous survey by February 20th. Thank you in advance for taking it!

Click here to take survey

or cut and paste the address directly:

https://www.surveymonkey.com/s/THWXVCD

I will issue the next advisory tomorrow morning at 7am. If you get out in the backcountry give us a call at 754-2369 or send us your observations using the button at the top of this page. Thanks and have a great day.

The NWS weather forecast for:

WESTERN PRINCE WILLIAM SOUND-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKST THU FEB 10 2011

…STRONG WIND NEAR WHITTIER AND SEWARD TONIGHT THROUGH SATURDAY

MORNING…

.TODAY…RAIN AND SNOW SHOWERS LIKELY. LITTLE SNOW ACCUMULATION.

HIGHS IN THE 30S. NORTH TO WEST WINDS 10 TO 20 MPH. GUSTS TO 30 MPH

THIS AFTERNOON.

.TONIGHT…SNOW SHOWERS…MIXED WITH RAIN IN THE EVENING. SNOW

ACCUMULATIONS UP TO 2 INCHES. LOWS IN THE LOWER TO MID 20S. NORTH TO

WEST WINDS 10 TO 25 MPH. NEAR SEWARD AND WHITTIER…NORTH TO WEST

WINDS 20 TO 30 MPH WITH GUSTS TO 45 MPH.

.FRIDAY…MOSTLY CLOUDY WITH A SLIGHT CHANCE OF SNOW. HIGHS IN

THE 20S. NORTHWEST WIND 10 TO 20 MPH. NEAR SEWARD AND WHITTIER…

NORTH TO WEST WINDS 20 TO 35 MPH WITH GUSTS TO 50 MPH.

.FRIDAY NIGHT…PARTLY CLOUDY. LOWS 5 BELOW TO 15 ABOVE…COOLEST

INLAND. NORTHWEST WIND 10 TO 25 MPH. NEAR SEWARD AND WHITTIER…NORTH

TO WEST WINDS 20 TO 35 MPH WITH GUSTS 45 TO 55 MPH.

.SATURDAY…MOSTLY SUNNY. HIGHS 10 TO 20 ABOVE. NORTHWEST WIND

10 TO 25 MPH. NEAR SEWARD AND WHITTIER…NORTH TO WEST WINDS 20 TO 35

MPH. GUSTS 45 TO 55 MPH DIMINISHING IN THE AFTERNOON.

.SATURDAY NIGHT…MOSTLY CLEAR. LOWS ZERO TO 10 BELOW.

.SUNDAY THROUGH MONDAY…PARTLY CLOUDY. HIGHS ZERO TO 10 ABOVE.

LOWS 5 BELOW TO 15 BELOW.

TEMPERATURE / PRECIPITATION

SEWARD 38 25 27 / 60 60 20

GIRDWOOD 37 20 23 / 30 40 20

WEATHER STATION SUMMARY for Turnagain Pass:

-3800′ Sunburst Wx Station-

Temperature 23 degrees. Light wind gusting to 17mph recently.

-2600′ Seattle Ridge Wx Station-

Temperature 27 degrees. Light to moderate wind from the SE.

-1800′ Center Ridge Wx Station-

Temperature 28. 1-2 inches of snow fell Tuesday and Wednesday.

Thu, February 10th, 2011
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
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.