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ARCHIVED - Forecasts expire after 24 hours.
Issued
Tue, March 22nd, 2011 - 7:00AM
Expires
Wed, March 23rd, 2011 - 7:00AM
Forecaster
Jon Gellings
Avalanche risk The Bottom Line

Good morning backcountry travelers. This is Jon Gellings with the Chugach National Forest Avalanche Information Center on Tuesday, March 22nd 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

Today, the avalanche danger is LOW. Keeping distance from areas where likely trigger points occur is one way to manage breaking out stubborn old wind slabs. If new snow falls in our advisory area, we could start to see an increase in the avalanche danger. Until then, practicing standard safe travel techniques while in avalanche terrain should be enough to manage this hazard.

AVALANCHE DISCUSSION

Normal hazards are lingering in the backcountry of Turnagain Pass. There is an isolated chance of fracturing out an old wind slab on steep unsupported slopes, and breaking cornices could be a problem as well if someone is travelling on or underneath them. Any area of the Forest that receives new snow or rain could see an increase in avalanche danger as well.

This increase in danger will likely be attributed to instabilities at the old snow/new snow interface, but may also relight the possibility of triggering a deeper slab as well. With moderate winds forming new slabs, you can see how there is not quite enough transportable snow in Turnagain Pass to increase the hazard yet. Wind hammered slopes, coupled with daily heating and cooling, has created a snowpack that would need extreme winds to be able to transport old snow. New snow moves much easier, so we will monitor the situation for any changes.

Though outside of our advisory area, the avalanche up in Hatcher Pass brings back to mind the dangerous nature of the shallow and weak snowpack that has plagued CNFAIC Staff areas this winter. Thin snow tends to mean weak snow, and weak snow should be thought of as “guilty until proven innocent.” The formation of facets underneath an old slab leads more to the guilty side, so finding any amount of these weak snow grains signifies that you are in one of these shallow snowpack areas. Summit Lake has been showing us signs of having a shallow snowpack all winter, and any new weight in the form of snow or rain in these areas could revitalize any dormant instabilities. However, this is all speculation until we actually see it; we need more precipitation for that to happen.

Encyclopedia of avalanche terms.

WEATHER ROUNDUP

Winds look like they should be reaching into the 30mph range, which is enough to blow around the top dusting of surface snow, which there is not enough of to create large wind slabs. Temperatures should be similar to yesterday, approaching the freeze threshold in the afternoon. New precipitation is possible, but more likely to the south of Turnagain Pass. This will likely not increase the danger in the Pass itself, but might at the south end of the Forest.

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 AKDT TUE MAR 22 2011

.TODAY…SNOW FROM MOOSE PASS SOUTH…BECOMING MIXED WITH RAIN AT

TIMES IN THE AFTERNOON. SNOW ACCUMULATION 1 TO 2 INCHES. MOSTLY

CLOUDY WITH SCATTERED SNOW SHOWERS ELSEWHERE. HIGHS IN THE LOWER 30S

TO LOWER 40S. WARMEST MOOSE PASS SOUTHWARD. VARIABLE WINDS TO 15 MPH

EXCEPT EAST WIND 15 TO 30 MPH THROUGH PORTAGE VALLEY AND ALONG

TURNAGAIN ARM.

.TONIGHT…SNOW FROM MOOSE PASS SOUTHWARD…MIXED WITH RAIN AT TIMES

IN THE EVENING. SNOW ACCUMULATION 1 TO 2 INCHES. MOSTLY CLOUDY WITH

SCATTERED SNOW SHOWERS ELSEWHERE. LOWS IN THE LOWER 20S TO LOWER

30S. COOLEST NORTH OF MOOSE PASS. NORTH TO EAST WIND 10 TO 20 MPH

EXCEPT EAST 20 TO 35 MPH THROUGH PORTAGE VALLEY AND ALONG TURNAGAIN

ARM.

.WEDNESDAY…SNOW AND RAIN LIKELY MOOSE PASS SOUTHWARD. ADDITIONAL

SNOW ACCUMULATION UP TO 1 INCH. MOSTLY CLOUDY WITH SCATTERED SNOW

AND RAIN SHOWERS ELSEWHERE. HIGHS IN THE MID 30S TO LOWER 40S.

VARIABLE WINDS TO 15 MPH EXCEPT EAST WIND 10 TO 25 MPH THROUGH

PORTAGE VALLEY AND ALONG TURNAGAIN ARM.

.WEDNESDAY NIGHT…SNOW SHOWERS LIKELY. LOWS IN THE 20S. NORTHEAST

WIND 10 TO 20 MPH.

TEMPERATURE / PRECIPITATION

SEWARD 37 30 39 / 90 90 70

GIRDWOOD 37 26 37 / 40 40 50

WEATHER STATION SUMMARY for Turnagain Pass:

-3800′ Sunburst Wx Station-

16 degrees. East wind 7mph gusting to 18mph.

-2600′ Seattle Ridge Wx Station-

18 degrees. Southeast wind 18mph gusting to 27mph.

-1800′ Center Ridge Wx Station-

24 degrees. No new snow.

Tue, March 22nd, 2011
Alpine
Above 2,500'
1 - Low
Avalanche risk
Treeline
1,000'-2,500'
1 - Low
Avalanche risk
Below Treeline
Below 1,000'
1 - Low
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.