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ARCHIVED - Forecasts expire after 24 hours.
Issued
Tue, March 29th, 2011 - 7:00AM
Expires
Wed, March 30th, 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 29th 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 danger will increase to CONSIDERABLE today. Center Ridge is reporting 9 inches of new snow currently. Naturals are possible in low to mid-elevation areas that are getting rained on, while Human triggered avalanches are likely in upper elevation areas, where newly deposited wind slabs are likely to be touchy to any additional weight, breaking into persistent weak layers above the wind-hammered snow from the past month. It is worth mentioning that Girdwood Valley has received more precipitation than Turnagain Pass, creating an increased danger for the area.

AVALANCHE DISCUSSION

One new avalanche has been reported from the Turnagain Pass area. Information is limited, but what has been stated is that it was on the South aspect of Tincan Peak, at the far end of Center Ridge. It broke about a foot deep and ran big on either a layer of buried surface hoar, or in a radiation recrystallized layer. Any new information will be posted when and if it becomes available.

A new layer of up to 2cm surface hoar is currently getting buried. It has been seen on many aspects and elevations throughout the Pass, and is now buried beneath several inches of new, wet heavy snow. It is more concerning on South aspects, where it is sitting on top of a sun crust from 2-3 days ago. In non-sun affected places, it is sitting on fluffy snow, which could heal itself over time, but is currently acting as a weak layer for the warm and heavy snow falling right now. Many areas with rain-on-snow have likely already released, but any place that hasn’t could do so today. Signs that you are on unstable snow include seeing shooting cracks, hearing whumpf sounds, feeling collapses, or travelling on hollow feeling/sounding snow.

All of the above is happening on top of the previously buried layers of surface hoar and near-surface facets above the wind-affected snow from earlier this month. Avalanches running down to this layer in wind-loaded terrain could break up to 2-3ft deep. It will likely take several days of warmth to get through this old layer, so most of the avalanches we see today will confidently be running above this layer. There is always a chance for breaks into and below this layer, but they would be isolated events at best.

Lastly, areas with a shallow snowpack have a slight potential for breaking into deep layers. This statement is more geared toward Summit Lake, Johnson Pass, and Crow Pass, but isolated spots in steep, rocky, unsupported terrain of Turnagain Pass have also shown signs of a shallow snowpack. Keep a lookout for, and avoid, any likely trigger points.

Encyclopedia of avalanche terms.

WEATHER ROUNDUP

Winds should be blowing snow around out there today, and are forecasted to reach into the 30 mph range, gusting into the 40s. Temperatures at the highway aren’t looking like they will freeze up today. Above that, the fluctuating freezeline is forecasted to around 1400ft. Precipitation will definitely be in the area today, as evidenced by satellite, radar, forecast, and model images, and we are forecasted to receive around 1 inch of SWE over the next 24hrs.

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 29 2011

…STRONG WIND TODAY THROUGH PORTAGE VALLEY AND TURNAGAIN ARM…

.TODAY…RAIN AND SNOW. SNOW ACCUMULATION UP TO 2 INCHES AT HIGHER

ELEVATIONS. HIGHS IN THE MID 30S TO LOWER 40S. THROUGH PORTAGE VALLEY

AND TURNAGAIN ARM…EAST WIND 25 TO 35 MPH WITH GUSTS TO 45 MPH.

NORTH TO EAST WINDS 15 TO 30 MPH ELSEWHERE.

.TONIGHT…RAIN AND SNOW. SNOW ACCUMULATIONS UP TO 2 INCHES…MAINLY

AT HIGHER ELEVATIONS AND INLAND. LOWS IN THE UPPER 20S TO MID 30S.

THROUGH PORTAGE VALLEY AND TURNAGAIN ARM…EAST WIND 15 TO 30 MPH

DIMINISHING TO 10 MPH BY MIDNIGHT. NORTH TO EAST WINDS 5 TO 15 MPH

ELSEWHERE.

.WEDNESDAY…RAIN AND SNOW LIKELY IN THE MORNING…THEN A CHANCE OF

RAIN AND SNOW SHOWERS IN THE AFTERNOON. NO SNOW ACCUMULATION. HIGHS

AROUND 40. VARIABLE WIND TO 10 MPH. NEAR SEWARD…NORTH WIND 10 MPH.

TEMPERATURE / PRECIPITATION

SEWARD 41 33 43 / 80 80 60

GIRDWOOD 39 30 42 / 70 80 40

WEATHER STATION SUMMARY for Turnagain Pass:

-3800′ Sunburst Wx Station-

24 degrees. ENE wind 29mph gusting to low 40s.

-2600′ Seattle Ridge Wx Station-

27 degrees. SE wind 21mph gusting to 31mph.

-1800′ Center Ridge Wx Station-

30 degrees. 9-10 inches new snow.

Tue, March 29th, 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.