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Issued
Mon, April 5th, 2010 - 7:00AM
Expires
Tue, April 6th, 2010 - 7:00AM
Forecaster
CNFAIC Staff
Avalanche risk The Bottom Line

Good morning backcountry travelers this is Lisa Portune with the Chugach National Forest Avalanche Information Center on Monday, April 5th 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).

ANNOUNCEMENTS

Skookum Valley and Skookum Glacier are closed to motorized vehicles (snowmachines, helicopters, ATVs) except for subsistence uses. This closure is directed in the current Chugach National Forest Land and Resource Management Plan. Placer River Drainage remains open for motorized use to Spencer Glacier.

WEATHER ROUNDUP

The Easter Bunny delivered the goods yesterday in the form of 19 inches of new snow at Turnagain Pass and 16 inches at Grandview. The upper elevations of the Girdwood Valley got anywhere from 12-24 inches of new snow. Ridgetop winds on Sunburst have been averaging 20-35mph out of the east with gusts to 51mph since noon yesterday while the winds on Seattle Ridge have been a bit lighter, averaging 15-30mph out of the southeast. Mountain temperatures yesterday only made it up to the mid 20’s to mid 30’s while a rain/snow mix fell at sea level throughout the day. As of 4am this morning, it is snowing at sea level while ridgetop winds are averaging 15-20mph out of the east. Temperatures range from 20F@3800′ to 27F@1800′ to 33F@sealevel. Winds should gradually taper off today, but the snow will continue to fall with 4-8 additional inches possible at the higher elevations by tomorrow morning. Mountain temperatures will hover around 20F at the upper elevations and 30F at the mid elevations. Winter is back!

AVALANCHE DISCUSSION

Today the avalanche danger has increased to CONSIDERABLE on all slopes greater than 35 degrees with areas of HIGH hazard on actively loading slopes above treeline. 16-19 inches of new snow plus strong easterly winds means human-triggered avalanches are LIKELY. Dangerous avalanche conditions exist. Natural avalanches are also likely this morning on steep windy slopes above treeline. This new snow fell on slick sun-crusted southerly aspects as well as a widespread melt-freeze crust below 2000 feet elevation, both excellent sliding surfaces for this new slab of heavy dense snow. Of equal concern today are the multiple layers of buried surface hoar that formed last month in the top four feet of the snowpack. New snow avalanches triggered today could step down to these deeper layers. The next time we see the strong springtime sun, even for a short period of time, expect almost instant wet sluffs possibly triggering slab avalanches on steep southerly slopes.

Today’s advisory is pretty straightforward. You will trigger avalanches on steep slopes today. They will either be slab avalanches on windloaded terrain or large sluffs on steep non-wind affected slopes. Either way, there is a lot of new snow to move around. For once this year this storm came in “right-side up”, meaning temperatures started off warm and ended cool, a good thing in terms of stability and bonding with the old snow surface. Still, we need to let this snow settle out and stabilize for a few days.

Buried surface hoar on shaded northerly aspects was responsible for several human triggered avalanches a week ago that fractured 2-3 feet deep. On Saturday Jon and I found a layer of buried surface hoar 2 feet down on a north aspect of Magnum at 2400 feet. We got clean fast Q1 shears on this layer, a huge heads-up and an obvious sign of instability. The buried surface hoar layers are not widespread, which makes finding them somewhat of a crapshoot. Once this new snow settles out, make sure to dig down and evaluate each individual slope before diving in.

Matt 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 5 2010

.TODAY…SNOW. SNOW ACCUMULATION UP TO 4 INCHES. HIGHS IN THE MID

TO UPPER 30S. EAST WIND 10 TO 20 MPH EXCEPT EAST 20 TO 35 MPH

THROUGH PORTAGE VALLEY AND TURNAGAIN ARM AND NEAR WHITTIER.

.TONIGHT…SNOW LIKELY. SNOW ACCUMULATION UP TO 1 INCH. LOWS IN

THE MID 20S TO LOWER 30S. SOUTHEAST WIND 10 TO 20 MPH IN THE

EVENING BECOMING LIGHT. NEAR WHITTIER…EAST WIND 10 TO 20 MPH.

.TUESDAY…SNOW LIKELY. SNOW ACCUMULATION 1 TO 2 INCHES. HIGHS IN

THE 30S. LIGHT WINDS.

TEMPERATURE / PRECIPITATION

SEWARD 41 27 39 / 80 70 60

GIRDWOOD 39 25 38 / 80 60 60

WEATHER STATION SUMMARY for Turnagain Pass:

-3800′ Sunburst Wx Station-

recorded strong easterly winds since noon yesterday averaging 20-35mph with gusts to 51mph. The high temp yesterday was 23F at 11am. The current temp is 20F with winds averaging 20mph out of the east.

-2600′ Seattle Ridge Wx Station-

recorded moderate to strong southeasterly winds yesterday and last night averaging 15-30mph with gusts to 47mph. The high temp yesterday was 26F. The current temp is 24F with winds averaging 15mph out of the southeast.

-1800′ Center Ridge Wx Station-

recorded 19 inches of new snow and 1.5 inches of water in the last 24 hours. The high temp yesterday was 35F at 1pm. The current temp is 27F with a total snowpack depth of 156 inches.

Mon, April 5th, 2010
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.