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Issued
Fri, April 1st, 2011 - 7:00AM
Expires
Sat, April 2nd, 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 Friday, April 1st 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’s avalanche danger rating is MODERATE for recent snow on top of buried surface hoar and wet slab activity this afternoon. The buried surface hoar is showing unsettling test pit results and deserves some respect. Warm temperatures this afternoon will likely cause some wet slab activity on Southern aspects.

AVALANCHE DISCUSSION

The peak of the recent storm was 3 days ago. Time is a good equalizer for storm snow avalanche problems, but we have some persistent weak layers to worry about. We’ve been finding lots of buried surface hoar in our field observations, which is keeping me a little worried about the snowpack.

Primary concern today is storm snow over buried surface hoar. We found 2 feet of settled snow sitting on a very weak layer of frost feathers above the firm March wind hammered snow. Take a look at our pit profile here.

The test results are what really grabbed my attention. The first isolated column failed with the first light tap I gave it, showing very poor strength. The video below shows an extended column test with moderate strength and the possibility for the weakness to propagate.

CNFAIC Staff definitive information about this weakness is the natural and human triggered avalanche activity that happened during and after the storm on Tuesday. There were a number of reported sympathetic avalanches (one avalanche triggering a second disconnected avalanche). This behavior indicates a collapsing weak layer (buried surface hoar) and conditions that can be difficult to manage safely. The surface hoar is widely distributed to the ridgetops and on all aspects. Take a look at anCNFAIC Staff recent avalanche in the photo gallery here.

Secondary concern today will be afternoon sun and rising temperatures. Sunny southern slopes will have a stiff sun crust this morning from yesterday’s afternoon melting and cold temperatures overnight. Today is forecasted to be similar with partly cloudy skies and warm temperatures. There is the possibility for all that heat to trigger sluffs and slabs in the same weak layers we are most concerned about. This concern will spike in the late afternoon and only on Southern exposures.

Encyclopedia of avalanche terms.

WEATHER ROUNDUP

An inch of snow fell yesterday morning. Anchorage got the brunt of that squall, while Turnagain arm took the remnants. Temperatures last night dipped into the low to mid 20s. Today, partly cloudy skies with temperatures into the 30s (40s at sea level) and light wind.

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 FRI APR 1 2011

.TODAY…MOSTLY CLOUDY BECOMING PARTLY CLOUDY. HIGHS IN THE MID 30S

TO MID 40S. VARIABLE WIND TO 10 MPH.

.TONIGHT…MOSTLY CLOUDY WITH SCATTERED SNOW SHOWERS. LOWS IN THE

MID 20S TO LOWER 30S. VARIABLE WIND 10 MPH.

.SATURDAY…SNOW IN THE MORNING…THEN RAIN IN THE AFTERNOON. LITTLE

SNOW ACCUMULATION. HIGHS IN THE UPPER 30S TO MID 40S. EAST WIND 10 TO

15 MPH INCREASING TO 15 TO 30 MPH IN THE AFTERNOON. THROUGH PORTAGE

VALLEY AND TURNAGAIN ARM…EAST WIND 10 TO 15 MPH INCREASING TO 25 TO

45 MPH IN THE AFTERNOON.

.SATURDAY NIGHT…RAIN AND SNOW. LOWS IN THE UPPER 20S TO MID 30S.

NORTH TO EAST WIND 20 TO 35 MPH EXCEPT EAST 35 TO 50 MPH THROUGH

PORTAGE VALLEY AND TURNAGAIN ARM.

.SUNDAY…RAIN AND SNOW IN THE MORNING…THEN RAIN IN THE

AFTERNOON. HIGHS IN THE UPPER 30S TO MID 40S. EAST WIND 20 TO

35 MPH EXCEPT EAST 35 TO 50 MPH THROUGH PORTAGE VALLEY AND

TURNAGAIN ARM.

TEMPERATURE / PRECIPITATION

SEWARD 41 31 43 / 0 20 80

GIRDWOOD 39 29 39 / 0 40 80

WEATHER STATION SUMMARY for Turnagain Pass:

-3800′ Sunburst Wx Station-

Currently 20 degrees at 6am. Light West wind.

-2600′ Seattle Ridge Wx Station-

23 degrees at 6am. Light SE wind.

-1800′ Center Ridge Wx Station-

23 degrees at 6am. 1 inch new snow recorded yesterday.

Fri, April 1st, 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.