Good morning backcountry travelers this is Jon Gellings with the Chugach National Forest Avalanche Information Center on Tuesday, January 25th 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 danger rating remains at CONSIDERABLE today. With an additional 6 inches of new snow overnight and strong winds, there is still the possibility of Naturally triggered avalanches in windloaded terrain. Human triggered avalanches are likely as well in this terrain, and could fail several feet down in loaded areas. Shooting cracks are a sign of these windloaded areas, and are hinting that instability lurks in the snow where the failure occured.
Recent observations show that our snowpack is adjusting to its new snow load, but it will take some time for it to become more stable. Yesterday, shooting cracks on steep rollovers were observed on Tincan. A few small slab avalanches ripped out in the Johnson Pass valley on the newly buried layer of surface hoar, but the overall look of things was that the snow was becoming plastered to many slopes. Steeper areas will likely be able to fail with the additional weight of a human or snowmachine, so jumping around on terrain of this kind is not advised for today.
18-22 inches of upside-down snow has fallen over the past six days, which has buried a spectrum of significant weak layers, the most predominant being the widespread surface hoar that formed January 5-18. The new snow is sitting on top of variable conditions, which include ice crusts, wind crusts, wind slabs, and sugary facets. All of these layers are poor surfaces for our new snow to bond to, especially since the storm has warmed up after depositing the first several inches of cold and light density snow. Winds up in the start zones have pushed a lot of snow around, so expect possible failures to occur up to several feet deep in upper alpine areas.
While the new snow is getting most of our attention currently, we can not forget the CNFAIC Staff persistent instabilities that remain a secondary concern further down in our snowpack. These persistent weak layers consist of buried surface hoar that formed in December and facets above and below the Thanksgiving Rain Crust. Although it has been over two weeks since the last reported human triggered avalanche on one of these layers, the weight and added energy of our new snowfall has the potential to create new avalanche activity within these layers. Avalanches that are triggered today have the potential to step down to any of these deeper layers, which could create a much deeper and larger avalanche.
Encyclopedia of terms: www.fsavalanche.org/Encyclopedia.aspx
Radar images currently show a large parcel of precipitation moving toward our advisory area, while satellite images show the “eye” of the Low pressure system about to run into Seward and Prince William Sound. Rain is currently falling on my roof in Girdwood, while data is showing snow falling at higher elevations, both in this valley as well as in Turnagain Pass. Models are showing cooling temperatures starting tonight, with decreasing winds starting at that time as well. The jet stream forecast is showing similar activity to our current situation for the next several days.
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 TUE JAN 25 2011
.TODAY…RAIN AND SNOW IN THE MORNING…THEN NUMEROUS RAIN AND SNOW
SHOWERS IN THE AFTERNOON. SNOW ACCUMULATION UP TO 2 INCHES OVER THE
HIGHER ELEVATIONS. HIGHS IN THE LOWER 30S TO LOWER 40S. NORTH TO EAST
WIND 15 TO 30 MPH.
.TONIGHT…NUMEROUS SNOW AND RAIN SHOWERS IN THE EVENING…THEN
SCATTERED SNOW SHOWERS AFTER MIDNIGHT. SNOW ACCUMULATION UP TO 1
INCH. LOWS IN THE LOWER 20S TO LOWER 30S. VARIABLE WIND TO 15 MPH.
.WEDNESDAY…CLOUDY WITH SCATTERED SNOW SHOWERS. HIGHS IN THE MID 20S
TO MID 30S. VARIABLE WIND TO 10 MPH. NEAR WHITTIER…WEST WIND 10 TO
.WEDNESDAY NIGHT…MOSTLY CLOUDY WITH SCATTERED SNOW SHOWERS. LOWS IN
THE LOWER TEENS TO LOWER 30S…COOLEST INLAND. VARIABLE WIND TO 10
MPH. NEAR SEWARD…NORTH WIND 10 MPH.
TEMPERATURE / PRECIPITATION
SEWARD 37 28 31 / 80 60 40
GIRDWOOD 38 21 23 / 80 60 40
WEATHER STATION SUMMARY for Turnagain Pass:
-3800′ Sunburst Wx Station-
recorded strong winds yesterday averaging 20-40mph, with a peak wind of 46 gusting out of the NE. Temperatures were recorded from 22F to 25F during the day. The winds are blowing 28-41mph out of the NE, while the temperature is currently 26F.
-2600′ Seattle Ridge Wx Station-
is currently not recording winds. Yesterday it recorded strong winds averaging 20-40mph gusting to 42 out of the SE. Temps increased from 22F to 28F during the day. Temp is currently 29F.
-1800′ Center Ridge Wx Station-
recorded 6 inches of new snow and 0.6 inches of water in the last 24 hours. Temps yesterday recorded from 30F to 34F during the day. The current temp is 31F.