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Issued
Mon, April 4th, 2011 - 7:00AM
Expires
Tue, April 5th, 2011 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

Good morning backcountry travelers. This is Wendy Wagner with the Chugach National Forest Avalanche Information Center on Monday, April 4th 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 CONSIDERABLE for both slab avalanches breaking into weak layers 2-5 feet deep and wind slabs formed in yesterday’s new snow. There is also a MODERATE danger for soft slab avalanches in the storm snow. If skies break up keep a close eye on any avalanchs from yesterday as this is bull’s eye data for slopes that are still prone to slide.

AVALANCHE DISCUSSION

Yesterday’s storm has slowed down. By the afternoon 14-16 inches of heavy snow accumulated at and below tree line on Turnagain Pass while Girdwood Valley picked up around 8-12 inches. The limited visibility kept travel in, and viewing of, higher elevations restricted. We are uncertain as to what yesterday’s high winds and new snow have produced for avalanches. What we do know is small, heavy, 12-16” deep soft slabs were breaking on the steeper rollovers below tree line. These soft slabs will likely be less sensitive today as the storm snow bonds and gains strength.

Most of the action is above tree line and the primary concern for today remains the buried weak layers which now sit under 2-5′ of snow. These weak layers are ‘persistent’ and have produced significant avalanches after the March 25th storm, the March 29th storm and, until proven innocent, likely yesterday’s April 3rd storm. Northerly aspects, with minimal to no crusts in the upper few feet of snow, are the most concerning. Watch for recent deeper avalanches as well as ‘whoomphing’ sounds. Steering clear of steeper slopes today is recommended.

The CNFAIC Staff concerns for today will be wind slabs that developed with the strong winds and soft slabs in the storm snow. Though these are likely to be less reactive with the warm temperatures and decrease in winds overnight, don’t count on it yet, they can still be sensitive to human triggers, especially as elevation increases. Shooting cracks will be something to watch for.

Take home for today: If skies open up enough to venture into the upper elevations high level snow assessment skills will be required for safe travel. Keep a close eye on any recent avalanches from yesterday. These will be bull’s eye data that slopes are potentially unstable. Particularly, steering clear of aspects and angles with recent slab avalanche activity is prudent.

Encyclopedia of avalanche terms.

WEATHER ROUNDUP

Snow showers continued yesterday with limited visibility, a total of 12-16″ of high density snow fell below 2300′ (likely more at higher elevations) near Turnagain Pass with Girdwood Valley 8-12” and the Summit Lake area only a few inches. Winds were light in sheltered locations while gusts around 50mph were reported from the ridgetop weather stations. Temperatures were in the mid 30’s at 1500′ and low 20’s around 3500′. Overnight, the snow and winds have let up while the temperature did not drop. Today lingering snow showers and cloudy skies remain with a chance to pick up a few more inches. Winds will be gusting to 30mph from the NE while temperatures will be on the rise well into the 30’s and 20’s at upper elevations with the rain-snow line near 1300′.

Jon 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 MON APR 4 2011

.TODAY…NUMEROUS SNOW AND RAIN SHOWERS IN THE MORNING BECOMING

NUMEROUS RAIN SHOWERS IN THE AFTERNOON. SNOW ACCUMULATION UP TO 2

INCHES. HIGHS IN THE MID 30S TO MID 40S. SOUTH TO EAST WIND 15 MPH.

THROUGH PORTAGE VALLEY AND TURNAGAIN ARM…SOUTHEAST WIND 10 MPH

INCREASING TO 25 MPH IN THE AFTERNOON.

.TONIGHT…SNOW AND RAIN LIKELY IN THE EVENING…THEN SNOW LIKELY

AFTER MIDNIGHT. SNOW ACCUMULATION UP TO 3 INCHES. LOWS IN THE

LOWER 20S TO MID 30S. SOUTHEAST WIND 15 TO 30 MPH.

.TUESDAY…SNOW IN THE MORNING…THEN SNOW AND RAIN IN THE AFTERNOON.

SNOW ACCUMULATION UP TO 2 INCHES. HIGHS IN THE MID 30S TO LOWER 40S.

SOUTH WIND 15 MPH BECOMING VARIABLE IN THE AFTERNOON.

.TUESDAY NIGHT…NUMEROUS SNOW AND RAIN SHOWERS IN THE EVENING…THEN

SCATTERED SNOW SHOWERS AFTER MIDNIGHT. LOWS IN THE MID 20S TO MID

30S. VARIABLE WIND TO 10 MPH. NEAR WHITTIER…LIGHT WINDS BECOMING

WEST 10 TO 20 MPH AFTER MIDNIGHT.

.WEDNESDAY…PARTLY CLOUDY. HIGHS IN THE LOWER 30S TO LOWER 40S…

COOLEST INLAND. NORTHWEST WIND 10 TO 15 MPH EXCEPT WEST 15 TO 30 MPH

NEAR WHITTIER.

.WEDNESDAY NIGHT…MOSTLY CLOUDY. LOWS 25 TO 35.

.THURSDAY…MOSTLY CLOUDY WITH A CHANCE OF RAIN. HIGHS 35 TO 45.

TEMPERATURE / PRECIPITATION

SEWARD 42 30 40 / 60 60 80

GIRDWOOD 44 35 43 / 60 60 80

WEATHER STATION SUMMARY for Turnagain Pass:

-3800′ Sunburst Wx Station-

24 degrees. East wind 6mph gusting 11mph.

-2600′ Seattle Ridge Wx Station-

27 degrees. SE wind 11mph gusting 14mph.

-1800′ Center Ridge Wx Station-

30 degrees. Trace of new snow.

Mon, April 4th, 2011
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
3 - Considerable
Avalanche risk
Below Treeline
Below 1,000'
3 - Considerable
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.