Good morning backcountry travelers this is Lisa Portune with the Chugach National Forest Avalanche Information Center on Monday, April 12th 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).
Skookum Valley and Skookum Glacier are closed to motorized vehicles (snowmachines, helicopters, ATVs) except for subsistence uses. This closure is directed in the current Chugach National Forest Land and Resource Management Plan. Placer River Drainage remains open for motorized use to Spencer Glacier.
2-4 inches of new snow fell in the last 24 hours in Turnagain Pass. Ridgetop winds averaged 20-30mph out of the east yesterday while mountain temperatures warmed up to the low 20’s at the upper elevations and mid 30’s at the middle elevations. Looking out my window at 4am this morning, I see partial clearing through the thick clouds. The winds decreased a bit last night and are currently averaging 15mph on Sunburst and 20mph on Seattle Ridge while temperatures this morning range from 21F@3800′ to 29F@1800′ to 35F@sealevel. We may squeeze a few more inches of snow out of this system today before the next low moves in tonight. Ridgetop winds will be moderate to strong today, averaging 15-30mph out of the east, while mountain temperatures will be a carbon copy of yesterday.
Today the avalanche danger remains at MODERATE overall with areas of CONSIDERABLE hazard on windloaded slopes greater than 35 degrees. Newly formed windslabs up to 2 feet deep will be very sensitive to human triggers today. Shallow long-running sluffs are also likely on steep slopes not affected by the wind. Yesterday’s new and wind-driven snow buried a recently formed layer of surface hoar in addition to a slick suncrust on E-S-W aspects. Long running fractures are possible on the buried surface hoar. An outside chance also remains of triggering a deeper slab avalanche in thin, rocky starting zones in the upper elevations. If we see the strong springtime sun today, expect almost instant wet sluffs possibly triggering slab avalanches on steep southerly slopes.
Wind was definitely the big player yesterday. Even though 2-4 inches is not much new snow, there was plenty of existing powder to move around. Yesterday Matt, Adam, and I easily triggered new windslabs 6-18 inches deep and 20-60 feet wide on Tincan once we got into the higher elevation wind-affected terrain above treeline. The avalanches were running on a sizeable layer of surface hoar that formed this past Thursday and Friday. The feathery crystals range in size from ¼ inch at 2500 feet to ½ inch at 4300 feet, and on E-S-W aspects the surface hoar is sitting on a suncrust, an especially dangerous combination. On a steep non-wind-affected northwest facing slope at 2000 feet we triggered shallow sluffs that ran 100 feet on the recent surface hoar layer. I would tread very lightly today and stay off of big open windloaded slopes.
Before this latest storm, one of our observers reported intentionally ski-cutting several recently formed windslabs in the north-facing chutes on Pete’s North on Friday. The largest one ran 900 feet and was 40 feet wide by 1.5 feet deep. On Saturday, a skier triggered a small avalanche on Todd’s Run on the north side of Tincan that knocked him over but did not bury him. On Saturday Jon and I toured up Cornbiscuit and found an old layer of buried surface hoar 1.5 feet deep in one of the north facing chutes at 3200 feet. We got full propagation across the column during 3 separate Extended Column Tests (ECTP12,15,27), so we backed off of riding that enticing line. On the flipside, many steep north facing lines were skied this past week with no problems. Like we said before, the numerous layers of buried surface hoar that formed last month are highly variable in their distribution and sensitivity over aspect and elevation. Always make sure to dig down and evaluate each individual slope before committing to a line.
Six glide cracks avalanched this past week, three on Saturday. Everywhere I look there seems to be a new glide crack forming. Lucky for us, these things are easily avoidable. They have their own agenda so stay out from under them.
Matt will issue the next advisory tomorrow morning at 7am. This is my last advisory of the season. Thanks everyone for a great winter and see you next year.
The NWS weather forecast for:
WESTERN PRINCE WILLIAM SOUND-
500 AM AKDT MON APR 12 2010
.TODAY…RAIN AND SNOW LIKELY IN THE MORNING…THEN RAIN LIKELY
IN THE AFTERNOON. SNOW ACCUMULATION UP TO 1 INCH. HIGHS AROUND 40.
SOUTH TO EAST WIND 10 TO 25 MPH EXCEPT SOUTHEAST 20 TO 35 MPH
THROUGH PORTAGE VALLEY AND TURNAGAIN ARM.
.TONIGHT…RAIN CHANGING TO SNOW AFTER MIDNIGHT. SNOW ACCUMULATION
UP TO 3 INCHES. LOWS IN THE UPPER 20S TO MID 30S. SOUTH TO EAST
WIND 15 TO 30 MPH WITH GUSTS TO 40 MPH THROUGH PORTAGE
VALLEY AND TURNAGAIN ARM…BECOMING SOUTH TO WEST 15 TO 30 MPH
.TUESDAY…PARTLY CLOUDY WITH A CHANCE OF SNOW SHOWERS IN THE
MORNING…THEN MOSTLY CLOUDY WITH A SLIGHT CHANCE OF RAIN AND
SNOW SHOWERS IN THE AFTERNOON. HIGHS AROUND 40. SOUTH TO WEST
WIND 10 TO 20 MPH.
TEMPERATURE / PRECIPITATION
SEWARD 40 32 40 / 70 100 20
GIRDWOOD 38 31 38 / 60 100 30
WEATHER STATION SUMMARY for Turnagain Pass:
-3800′ Sunburst Wx Station-
recorded moderate to strong easterly winds yesterday averaging 20-30mph with gusts to 51mph. The high temp yesterday was 22F at 1pm. The current temp is 21F with winds averaging 15mph out of the east.
-2600′ Seattle Ridge Wx Station-
recorded moderate to strong southeasterly winds yesterday averaging 20-30mph with gusts to 44mph. The high temp yesterday was 25F. The current temp is 24F with winds averaging 20mph out of the southeast.
-1800′ Center Ridge Wx Station-
recorded 1 inch of new snow and 0.1 inches of water in the last 24 hours. The high temp yesterday was 38F at 2pm. The current temp is 29F with a total snowpack depth of 142 inches.