Good morning backcountry travelers this is Kevin Wright with the Chugach National Forest Avalanche Information Center on Friday, February 11th 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).
The avalanche hazard rating is MODERATE. If the current storm accumulates, the hazard could increase through the day to CONSIDERABLE. The older deeper weak layers are still prevalent and harder to trigger but potentially more dangerous than the new storm snow. Any new added stress in the form of new snow will bring the snowpack closer to the point of failure and avalanching.
The small storm a couple days ago is fading into the past, but anCNFAIC Staff low is currently affecting the region with new ongoing snowfall, colder temperatures, and light wind. It’s tough to tell how much snow we’ll get from this one. If it accumulates without wind it could make quality riding conditions without forming the sensitive wind slabs that we got from the last storm. Any new snow will add weight and stress to the snowpack and make triggering deeper instabilities more likely. The degree that the new snow affects stability is directly related to the amount we get.
The most recent avalanche in Turnagain pass was the skier triggered slide on the South face of Magnum on Monday (see photo below). Since that time nothing has changed to stabilize the responsible weak layers. Snowpit tests are showing the same failures near the Thanksgiving Rain Crust on 2-3mm (well developed, large) facets. This kind of slab will be possible to trigger today and through the weekend.
Over the last few days a lack of new human triggered avalanches is only because few people are in the backcountry right now. During the storm fewer people travel on the slopes and those who do stay on lower slope angles, at lower elevations, and near trees with good visual references. This means that nobody is testing the stability and we don’t get any feedback about the likelihood of human triggers. Don’t confuse a lack of bad information with good information right now.
Due to an inherently weak snow structure (strong, dense snow on top of weak snow) and many recent human triggered avalanches, Moderate is as low as the danger rating will get until major changes happen. The old weak layers may fail with each additional load until we have a truly significant storm that doesn’t produce avalanches on these layers. So far none of our recent storms have been anywhere near large enough.
Primary concern: Deep persistent instabilities. These are most likely to be affected in shallow zones like in the areas of Summit Lake or Johnson Pass. Also in deeper snowpacks around Turnagain pass and Girdwood be aware of likely trigger points in specific shallow areas near exposed or lightly buried rocks.
Encyclopedia of avalanche terms.
The last storm ended 2 days ago. That one brought more wind than snowfall. It dropped 2-3 inches in Turnagain pass, and closer to 1 foot in the mountains around Girdwood. The surface snow in Turnagain pass was wind stiffened everywhere except in sheltered areas.
Currently snow is falling with a moderate SE flow spilling over from Prince William Sound. Whittier is getting a direct hit and Turnagain Pass has gotten a few inches already. Temperatures have dropped quickly and the prediction is for negative temps and clearing skies over the next few days.
The Friends of the CNFAIC (FCNFAIC) needs your thoughts! With a new staff of forecasters and a list of previously completed goals, the program is growing and potentially heading in new directions. The FCNFAIC wants to know what you have to say about YOUR avalanche center, so please complete the following anonymous survey by February 20th. Thank you in advance for taking it!
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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 FEB 11 2011
…BLIZZARD WARNING IN EFFECT UNTIL 6 PM AKST THIS EVENING
…STRONG WIND THROUGH SATURDAY NIGHT NEAR WHITTIER AND SEWARD…
.TODAY…SNOW. AREAS OF BLOWING SNOW…VISIBILITIES REDUCED AT TIMES
TO ONE QUARTER MILE OR LESS NEAR WHITTIER. SNOW ACCUMULATION UP TO
2 INCHES. HIGHS IN THE 20S. NORTH TO WEST WINDS 15 TO 30 MPH. NORTH
WINDS 20 TO 35 MPH WITH GUSTS TO 50 MPH NEAR SEWARD. SOUTHWEST WINDS
30 TO 45 MPH WITH GUSTS TO 65 MPH NEAR WHITTIER.
.TONIGHT…SNOW ENDING IN THE EVENING. SLOWLY CLEARING FROM THE
SOUTHWEST. ADDITIONAL SNOW ACCUMULATIONS OF 1 INCH. AREAS OF BLOWING
SNOW…REDUCED AT TIMES TO ONE HALF MILE NEAR WHITTIER. LOWS 5 BELOW
TO 15 ABOVE…COOLEST INLAND. NORTH TO WEST WINDS 15 TO 30 MPH. NORTH
WINDS 20 TO 35 MPH WITH GUSTS TO 55 MPH NEAR SEWARD. SOUTHWEST WINDS
30 TO 45 MPH WITH GUSTS TO 65 MPH NEAR WHITTIER.
.SATURDAY…SUNNY. HIGHS 5 TO 15 ABOVE. NORTH TO WEST WINDS 15 TO 30
MPH. NORTH WINDS 20 TO 35 MPH WITH GUSTS TO 55 MPH NEAR SEWARD.
SOUTHWEST WINDS 30 TO 45 MPH WITH GUSTS TO 65 MPH NEAR WHITTIER.
.SATURDAY NIGHT…MOSTLY CLEAR. LOWS 5 BELOW TO 10 BELOW EXCEPT
5 TO 10 ABOVE NEAR SEWARD AND WHITTIER. NORTHWEST WIND 10 TO
25 MPH EXCEPT WEST 35 TO 50 MPH NEAR WHITTIER. NORTH WINDS 25 TO 45
MPH NEAR SEWARD.
.SUNDAY…PARTLY CLOUDY WITH A SLIGHT CHANCE OF SNOW SHOWERS.
HIGHS 5 BELOW TO 10 ABOVE…COOLEST INLAND.
NORTHWEST WIND 10 TO 25 MPH EXCEPT WEST 35 TO 50 MPH NEAR
.SUNDAY NIGHT…PARTLY CLOUDY. LOWS 5 BELOW TO 15 BELOW.
.MONDAY…MOSTLY SUNNY. HIGHS ZERO TO 10 ABOVE.
.MONDAY NIGHT AND TUESDAY…CLEAR. LOWS 5 BELOW TO 15 BELOW.
HIGHS IN THE TEENS.
TEMPERATURE / PRECIPITATION
SEWARD 25 11 12 / 80 0 0
GIRDWOOD 22 4 9 / 80 60 0
WEATHER STATION SUMMARY for Turnagain Pass:
-3800′ Sunburst Wx Station-
Temperature 15 degrees and falling. Light and variable wind.
-2600′ Seattle Ridge Wx Station-
Temperature 12 degrees and falling. Wind gauge iced over.
-1800′ Center Ridge Wx Station-
Temperature 18 degrees and falling. A couple inches new snow has fallen since yesterday.