Good morning backcountry travelers this is Jon Gellings with the Chugach National Forest Avalanche Information Center on Wednesday, December 15th 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).
Today the avalanche hazard will remain MODERATE overall. Natural avalanches are unlikely, but small human triggered avalanches are possible in steep terrain in upper elevation areas, where winds have potentially created wind slabs out of our soft surface snow.
A few days ago, we received a report of a small skier triggered avalanche somewhere in the Magnum/Cornbiscuit area, as well as a report of a partial snowmachine burial outside of our advisory area to the South. Of the two different incidents, the snowmachine triggered avalanche was of a much larger size. Keep in mind that MODERATE states that large avalanches can occur in isolated areas… exactly what happened here:
It is unclear what layer failed and created the avalanche, but it was likely a buried layer of surface hoar. Several surface hoar layers formed from the valley bottoms to the ridgetops nearly everywhere in Turnagain Pass and were covered up by small amounts of snow here and there over the last week. We will be monitoring these layers for increased activity until they no longer present a threat.
On anCNFAIC Staff issue, the Thanksgiving Rain Crust is continuing to show signs of the faceting process both above and below it. Observations point to the fact that it is not currently our weakest layer, but its overall individual stability trend is decreasing strength with low energy. It is currently buried at all elevations and aspects, and is buried up to 1.5 feet deep. Collapses, as well as no failures are observed in random terrain areas when doing stability tests. As of right now, no avalanches have been reported that have definitively broken down to this layer, but it is definitely a persistent instability of concern. Once we get a large storm, this layer could become more reactive, but it is currently fairly benign in most terrain.
We had beautiful blue skies yesterday, with clouds here and there. Currently, the stars are visible in some areas, but there seem to be mostly clouds out there. Radar images are showing several sizable chunks of precipitation headed our way, and Satellite images are showing that a 978mb Low pressure system in the Gulf of Alaska is the reason for the clouds and precipitation. Winds have the potential to become Strong in our area, but seem to be packing a bigger punch at lower elevations luckily. The Gulf storm is not bringing a lot of water vapor up from the mid-latitudes, so do not expect large amounts of precipitation from this one. As far as temperatures go, look for them to stay fairly similar over the next few days.
Kevin 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 WED DEC 15 2010
…STRONG WIND THROUGH THURSDAY NIGHT NEAR WHITTIER…
…STRONG WIND THROUGH THIS AFTERNOON NEAR SEWARD…
.TODAY…MOSTLY CLOUDY WITH ISOLATED SNOW SHOWERS IN THE MORNING.
HIGHS 5 TO 20 ABOVE…COOLEST INLAND. NORTHWEST WIND 10 TO 20 MPH
EXCEPT NORTH 35 TO 50 MPH NEAR SEWARD. NEAR WHITTIER…SOUTHWEST WIND
30 TO 45 MPH WITH GUSTS TO 60 MPH.
.TONIGHT…PARTLY CLOUDY. LOWS 10 BELOW TO 5 ABOVE…COOLEST
INLAND. NORTHWEST WIND 10 TO 15 MPH EXCEPT NORTH 30 TO 40 MPH
NEAR SEWARD. NEAR WHITTIER…SOUTHWEST WIND 30 TO 45 MPH WITH GUSTS
TO 55 MPH.
.THURSDAY…MOSTLY SUNNY. HIGHS ZERO TO 15 ABOVE. NORTHWEST WIND
10 TO 15 MPH EXCEPT NORTH 25 TO 40 MPH NEAR SEWARD. NEAR
WHITTIER…SOUTHWEST WIND 30 TO 45 MPH WITH GUSTS TO 55 MPH.
TEMPERATURE / PRECIPITATION
SEWARD 19 6 14 / 30 0 0
GIRDWOOD 7 -3 7 / 20 0 0
WEATHER STATION SUMMARY for Turnagain Pass:
-3800′ Sunburst Wx Station-
recorded light West winds yesterday averaging 4-8mph and temps ranging from 7F to -3F. The current temp is 4F with light winds out of the Northeast.
-2600′ Seattle Ridge Wx Station-
recorded light North winds yesterday averaging 5-9mph, with temps ranging from 8F to -1F. The current temp is 5F with light winds out of the North.
-1800′ Center Ridge Wx Station-
recorded no new snow in the last 24 hours. Temps yesterday ranged from 11F to 3F. The current temp is 5F with a total snowpack depth of 52 inches.