Good morning backcountry travelers this is Kevin Wright with the Chugach National Forest Avalanche Information Center on Friday, January 7th 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).
Please submit your snow and avalanche observations! We had at least one significant human triggered avalanche yesterday in the Girdwood valley that was not reported. Reporting these events helps everyone understand the avalanche hazard and assists this forecast center in making accurate assessments. Everyone should be reporting observations like this by using the observation form on this website. Thanks!
The avalanche hazard rating is CONSIDERABLE today. Careful route finding and conservative decision making are essential in the backcountry today. The last storm ended less than 48 hours ago. The snowpack yesterday showed that humans can still trigger large avalanches. Today that danger still exists. The trend of this hazard is decreasing slowly over time, but the potential for large destructive avalanches is still elevated.
Skier triggered avalanche in Warmup Bowl, Seattle ridge yesterday.
This is a giant bull’s eye clue! Nature is shouting out a message that travel is dangerous right now. Numerous natural avalanches happened during and immediately after the last storm, and are evident all over Turnagain pass (see photo gallery for more examples). Some of these avalanches were very large and destructive. The South face of Sunburst propagated about 600 feet wide across several shallow gulleys and ridges. We confirmed yesterday that the sliding layer at the top is buried surface hoar, but lower on the slope it stepped into multiple different weak layers above and below the Thanksgiving Rain Crust.
Areas of concern include steeper slopes (30-45) degrees that received wind loading during the storm. The high wind event (100+mph) pushed much of the snow lower onto the slopes than we normally see. The skier triggered slide in Warmup Bowl yesterday was initiated near rocks in a shallower part of the slab. Rocks and shallow zones facilitate the growth of weaknesses in the snowpack.
It is recommended to stay on conservative, lower angle terrain. I think the possibility of natural avalanches is low unless a cornice sets off the slab underneath. Human triggers are the main issue right now. Even on flat terrain pay close attention to people traveling on steep slopes above you.
Primary concern: Persistent instabilities. The multiple weak layers that formed during the cold dry weeks of December are going to continue to be a problem. We have multiple layers of buried surface hoar in widespread but sporadic locations throughout our region. Deeper in the snow well-developed facets have proved to be a problem.
Encyclopedia of avalanche terms.
The weather we’re concerned about right now already happened. Over 20 inches of new snow and 2.5 inches of water fell during the recent storm. No new snow fell in the last 24 hours. Surface hoar formation has been prevalent to the ridge tops since yesterday. Wind was light to moderate over the last couple days with gusts to the mid 20s. Expect similar conditions today with sunny skies, temperatures in the 20s 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-
500 AM AKST FRI JAN 7 2011
.TODAY…SUNNY…EXCEPT MOSTLY CLOUDY ALONG TURNAGAIN ARM. HIGHS IN
THE LOWER 20S TO MID 30S…COOLEST INLAND. NORTHWEST WIND 10 TO 15
MPH EXCEPT WEST 20 TO 35 MPH NEAR WHITTIER.
.TONIGHT…MOSTLY CLEAR. LOWS 5 TO 25 ABOVE…COOLEST INLAND.
NORTHWEST WIND 10 TO 15 MPH EXCEPT WEST 15 TO 30 MPH NEAR WHITTIER.
.SATURDAY…PARTLY CLOUDY IN THE MORNING THEN BECOMING MOSTLY
SUNNY. HIGHS IN THE LOWER 20S TO LOWER 30S…COOLEST INLAND.
VARIABLE WIND TO 10 MPH. NEAR SEWARD…NORTH WIND 10 TO 25 MPH.
.SATURDAY NIGHT…PARTLY CLOUDY. LOWS 10 TO 25 ABOVE. VARIABLE WIND
TO 10 MPH. NEAR SEWARD…NORTH WIND 15 TO 25 MPH.
.SUNDAY…PARTLY CLOUDY. HIGHS IN THE UPPER 20S TO MID 30S.
VARIABLE WIND TO 10 MPH. NEAR SEWARD…NORTH WIND 10 TO 20 MPH.
.SUNDAY NIGHT…MOSTLY CLEAR. LOWS IN THE 20S.
.MONDAY THROUGH THURSDAY…PARTLY CLOUDY. HIGHS 25 TO 35. LOWS
15 TO 25.
TEMPERATURE / PRECIPITATION
SEWARD 30 19 32 / 0 0 0
GIRDWOOD 22 10 27 / 0 0 0
WEATHER STATION SUMMARY for Turnagain Pass:
-3800′ Sunburst Wx Station-
Temperatures in the low 20s. Light wind from the WNW.
-2600′ Seattle Ridge Wx Station-
Temperatures in the high teens. No wind readings.
-1800′ Center Ridge Wx Station-
Temperatures in the mid teens. A couple inches of total snow loss has happened since the storm due to settling.