Good morning backcountry travelers this is Carl Skustad with the Chugach National Forest Avalanche Information Center on Saturday, February 13th at 7 am. This will serve as a general backcountry avalanche advisory issued for Turnagain Arm Area with Turnagain Pass as the core advisory area (this advisory does not apply to highways, railroads, or operating ski areas).
We will be at the Iron Dog Safety Expo today. It runs from 10-4pm at the Denaina Center. If your not riding today come see us.
We got a little more rain and snow out of yesterday’s weather than expected. Alyeska and Portage got more rain and snow than did Turnagain Pass. Alyeska received 1.06 inches of water (12 inches of snow)and the Pass got .7(4-6 inches of snow). Even within Turnagain Pass, snow depth varied greatly. 1000 foot snow board depth readings yesterday where: Eddies-6″, Motorized lot-8″, Sunburst-2″, and Johnson – trace. Temps are cooling off this morning and the freeze line has dipped close to sea level. Winds are light with moderate to strong gusts out of the east and southeast in the alpine.
Cloudy skies but no precipitation forecasted for today. Rain and snow will resume tonight and Sunday. The radars show limited precipitation and the satellite shows scattered cloud cover. I checked the jet stream models this morning. By Thursday we could be looking at a very south to north flow. This kind of jet brings very wet, very warm air from a long Pacific fetch.
Today’s avalanche hazard will remain MODERATE with pockets of CONSIDERABLE. This means that natural avalanches are unlikely, human triggered avalanches are possible. By avalanche hazard definition today is in between Moderate and Considerable. Today human triggered avalanches are certainly possible (moderate), I think they’re more likely than possible (considerable). Either way today is anCNFAIC Staff heads up day!
Lots of good observations from yesterday to report. Widespread shooting cracks and collapsing (whoophing) in the snowpack. A large natural avalanche occured on the face of Petes North. CNFAIC Staff smaller ones also observed in that area. Intentional small skier triggered avalanche on Tincan. Large artilary triggered avalanches observed between Girdwood and Portage.
All this avalanche activity is failing on a layer of buried surface hoar that is located 2-3 ft. deep. This is not the rain crust from early January (that’s 4-5 ft deep and could still be triggered with a large enough load). This buried surface hoar is much more reactive and needs to be respected. This type of weak layer is the one responsible for many avalanche fatalities. The shooting cracks and collapsing snowpack indicates energy in the surface slab and that a failure is occuring. If the slope angle is steep enough there will be an avalanche. I don’t think we will see any natural avalanche activity today, but human triggered avalanches are likely. Areas with an increased chance of triggering an avalanche today include: slopes steeper than 30 degrees, steep convex rollovers, and wind loaded ridges. The slab will be 1-3 feet thick. Part of my concern today stems from a test that Jon and Tim did yesterday at 1700 ft on Tincan. An extended column test failed very clean (Q1-2) with full propagation, down 3.5 ft. They also ski triggered a small avalanche at 2200 ft that failed 1.5 feet deep (CTM 14/16 Q2). The natural avalanche and observations from Petes North also point to the same weak layer. BURIED SURFACE HOAR! Careful route finding and slope angle selection will be key today. Have an exit plan in mind and stay away from terrain traps. Practice good backcountry travel rituals and you should have a great day in the mountains.
WEATHER FORECAST (National Weather Service)
WESTERN PRINCE WILLIAM SOUND-
500 AM AKST SAT FEB 13 2010
.TODAY…MOSTLY CLOUDY. PATCHY MORNING FOG. HIGHS IN THE MID 30S TO
LOWER 40S. VARIABLE WIND TO 15 MPH.
.TONIGHT…RAIN AND SNOW DEVELOPING AFTER MIDNIGHT. SNOW
ACCUMULATION UP TO 2 INCHES THROUGH TURNAGAIN PASS. LOWS IN THE MID
20S TO MID 30S. NORTH TO EAST WIND 10 TO 20 MPH. THROUGH PORTAGE
VALLEY AND TURNAGAIN ARM…VARIABLE WIND 10 MPH BECOMING EAST 15 TO
30 MPH AFTER MIDNIGHT.
.SUNDAY…RAIN. HIGHS IN THE MID 30S TO LOWER 40S. NORTH TO EAST
WIND 10 TO 25 MPH EXCEPT EAST 25 TO 40 MPH THROUGH PORTAGE VALLEY
AND TURNAGAIN ARM.
.SUNDAY NIGHT…RAIN AND SNOW SHOWERS. LOWS IN THE 30S. EAST WIND 15
TO 35 MPH EXCEPT EAST 35 TO 55 MPH THROUGH PORTAGE VALLEY AND
.PRESIDENTS DAY…RAIN AND SNOW SHOWERS. HIGHS IN THE MID 30S TO
LOWER 40S. SOUTHEAST WIND 15 TO 30 MPH EXCEPT EAST 30 TO 45 MPH
THROUGH PORTAGE VALLEY AND TURNAGAIN ARM.
.MONDAY NIGHT…NUMEROUS RAIN AND SNOW SHOWERS. LOWS IN THE 30S.
TEMPERATURE / PRECIPITATION
SEWARD 38 32 41 / 0 90 80
GIRDWOOD 37 29 37 / 0 60 70
Thanks for checking today’s avalanche advisory. The next one will be posted tomorrow Sunday, February 14th.