Good Morning backcountry travelers, this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Wednesday, February 25, 2009 at 7am. This will serve as a general backcountry avalanche advisory issued 5 days a week Wednesday-Sunday for the Turnagain Arm area(Turnagain Pass is the core advisory area). Local variations always occur. This advisory does not apply to operating ski areas or highway/railroad corridors.
MOUNTAIN WEATHER ROUND UP FOR THE LAST 24 HOURS
-General Weather Observations-
Temps are 4-10 degrees colder at most weather stations compared to yesterday morning. There is still a slight inversion between the colder sea level temps and warmer ridgetops. Temps were the warmest between 1pm and 3 pm on ridgetops yesterday reaching as high as 44 degrees on Sunburst. Winds at all ridgetop weather stations have been light and variable. The SNOTEL sites at Summit, Grandview, and Turnagain Pass all recorded zero new precip.
–The DOT weather station near the crest the highway at Turnagain Pass at 1000 feet–
Is recording a temp of 33 degrees (same as yesterday) with light winds. High temp yesteday was 43 degrees at 1pm.
–The NRCS Center Ridge weather station at 1800 feet in Turnagain Pass–
Has a temp of 21 degrees (4 degrees colder than yesterday). Zero new inches of water and zero inches of new snow has been recorded. Total snowpack depth is 67″. High temp was 33 degrees at 3pm.
–The Sunburst weather station at 3800 feet in Turnagain Pass–
Shows a temperature of 15 degrees (6 degree colder than yesterday). Winds have been calm to light averaging 0-9mph out of the W with a max gust of 18mph. High temp yesterday was 44 degrees at 2pm.
-Surface Analysis Maps-
Between 3am and 9pm yesterday….Show anCNFAIC Staff Bering Sea storm building in strength (990-982mb) as its heading towards Bristol Bay and the west coast of AK. It has a small outer arm of moisure.
Primary avalanche concerns
-Above 3000 feet. Hard wind slabs. Multiple density layers/interfaces in the top 1-2 feet of snow with potential for human-triggered avalanches.
-Below 3000 feet. Rain crust buried under 1-4 feet of surface snow. Avalanches have been common and widespread on this lower elevation instability. There is a layer of faceted snow on top and below this rain crust. Be very careful on steep slopes in Lost Lake, Placer Valley, Seattle Creek, and Girdwood Valley. This weak layer will be a problem for a while.
AVALANCHES AND SNOWPACK
Elevated Caution is advised today. The danger rating has generally decreased to MODERATE since this weekend; HOWEVER, there are still pockets of CONSIDERABLE hazard out there. Right now, my level of uncertainty with the snowpack is very high.
I don’t really know what is going on right now, but I do know that I don’t completely trust the snowpack. I’m trying to look at the facts and data, and NOT rely on my gut instincts.
Here’s some facts (with a few opinions too)
-That rain crust below 3000 feet continues to show itself. My stability tests in Main Bowl yesterday found hard failures (CTH20Q2) on the facets on top of that crust. Technically those scores show slightly less stability than last week’s tests; but, those test scores are debatable. I think the big picture is more along the lines that this weak layer is still a major issue. A guy from Lost Lake reported the worst avalanche conditions he has seen in 25 years on this rain crust. One of our observors found that rain crust yesterday on the Sunnyside opposite of Warm Up Bowl (lookers left of Repeat Offender if you are looking from the highway). In his extended column test, he found propogation across the entire column with a very clean and fast Q1/Q2 shear. We do not see many Q1 shears. Lisa saw the first Q1 of the season on Tincan on Saturday. Q1s are bad. Anytime you see super fast clean shears, you should stay away from those slopes. That observer that found this Q1/Q2 and his partner chose not to ski that slope, and came back down the snowmachine up-track. That guy from Lost Lake is worried about deadly avalanches on that layer after the next big storm, and I agree with him. Plus, I think there is potential for deadly avalanches on this rain crust layer today. Take a look at the photo gallery pictures of the natural avalanche in Skookum and the artillery triggered avalanche on the Moneys for examples of how destructive this weak layer can get.
-The surface snow has been very wind hammered creating widespread hard slabs all over the place. The bad thing about hard slabs is that sometimes they let you get out in the middle of them before they avalanche. CNFAIC Staff times they shatter right at the tip of your skis. We have found multiple interfaces and moderate to poor stability in the top 1-2 feet of surface snow over the past couple days. There has been reports of buried surface hoar mixed in the surface snow, but I have not been able to find it. Look at the photo from Lipps where a guy triggered a hard slab while skinning up.
-The sun has been warming rocks and creating sun sluffs. Most of these sluffs have tumbled down slope with minor consequences, but some have kicked off slab avalanches in the surface snow on their way down.
Safe terrain management and strict travel rituals are still essential right now.
WESTERN PRINCE WILLIAM SOUND-
500 AM AKST WED FEB 25 2009
…STRONG WIND THURSDAY MORNING…
.TODAY…INCREASING CLOUDS. HIGHS IN THE 30S. LIGHT WINDS BECOMING
SOUTHEAST TO 15 MPH IN THE AFTERNOON.
.TONIGHT…SNOW IN THE EVENING…THEN SNOW SHOWERS AFTER
MIDNIGHT. SNOW ACCUMULATION UP TO 3 INCHES. LOWS IN THE UPPER
TEENS TO MID 20S. SOUTH WIND 10 TO 20 MPH.
.THURSDAY…CLOUDY WITH SCATTERED SNOW SHOWERS. HIGHS IN THE MID
20S TO LOWER 30S. LIGHT WINDS BECOMING NORTH AND WEST TO 15 MPH IN
TEMPERATURE / PRECIPITATION
SEWARD 37 25 27 / 0 60 40
GIRDWOOD 32 24 29 / 0 80 40
This concludes today’s avalanche advisory the next advisory will be on Thursday, February 26th. Thanks and have a great day.