Good Morning backcountry travelers, this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Thursday, February 26, 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 resorts or highways/railroads.
MOUNTAIN WEATHER ROUND UP FOR THE LAST 24 HOURS
-General Weather Observations-
The temperature inversion has broken, temps are now warmer at sea level than the ridgetops. Winds at all ridgetop weather stations have been light to moderate out of the SE and SW. The SNOTEL sites recorded a trace to 2 inches of new snow and .1-.3 inches of H20 from Summit, Grandview, Turnagain Pass.
–The DOT weather station near the crest the highway at Turnagain Pass at 1000 feet–
Is recording a temp of 37 degrees (4 degrees warmer than yesterday) with light winds and zero new snow.
–The NRCS Center Ridge weather station at 1800 feet in Turnagain Pass–
Has a temp of 19 degrees (2 degrees colder than yesterday). .1 inches water and 1 inch of new snow has been recorded. Total snowpack depth is still 67″.
–The Sunburst weather station at 3800 feet in Turnagain Pass–
Shows a temperature of 12 degrees (3 degrees colder than yesterday). Winds have been calm to moderate averaging 2-20mph out of the SE with a max gust of 34mph.
-Surface Analysis Maps-
Between 3am and 9pm yesterday….Show yesterdays storm getting weaker as it slammed into the west coast of AK (980-998mb). There is not much else out there for storms today, and the outer arm of this storm looks like it might have passed by us already.
Very light and scattered precip moving east
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 still advised. The danger rating is MODERATE from sea-level to ridgetops with pockets of CONSIDERABLE below 3000 feet. Right now, my level of uncertainty with the snowpack is still in the middle range.
I’m learning a few more things about our current snowpack, but I still don’t completely trust it. Yesterday on Sunburst, I found those hard wind slabs. I dug several hand pits until I got above the rain crust elevation. I wanted to see how the surface snow was bonding to that old slippery January hurricane layer above 3000 feet. I found multiple density layers in the top 1-2 feet of snow that failed in mulitple places on compression tests. The surface snow did appear to be bonding fairly well to the slippery January hurricane layer in this particular pit. The main problem with upper elevations today is that those hard slabs can sometimes be tricky. Its common for people to get way out in the middle of a hard slab before it avalanches. The photo gallery has a photo of an small hard slab avalanche that a guy triggered while skinning up Lipps last Saturday. Odds are, the surface snow has been creating stronger bonds since last Friday’s wind event which should bridge a lot of weight. It seems less likely for a human-triggered avalanche on those wind slabs, but elevated caution is still advised.
The biggest concern with our snowpack is the rain crust at lower elevations
-That rain crust below 3000 feet continues to show itself. One of our observors found that rain crust Tuesday 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 last 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.
A guy from Lost Lake submitted an observation this weekend stating that avalanche conditions at Lost Lake are the worst he has seen in 25 years. He is worried about deadly avalanches on that rain crust 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.
Safe terrain management and strict travel rituals are still essential right now.
WESTERN PRINCE WILLIAM SOUND-
500 AM AKST THU FEB 26 2009
.TODAY…CLOUDY WITH SCATTERED SNOW SHOWERS. HIGHS IN THE UPPER
20S TO MID 30S. NORTHWEST WIND 10 TO 15 MPH.
.TONIGHT…MOSTLY CLOUDY IN THE EVENING THEN BECOMING PARTLY CLOUDY.
LOWS IN THE UPPER TEENS TO MID 20S. NORTH AND WEST WIND 10 TO
20 MPH WITH GUSTS TO 35 MPH NEAR SEWARD AND WHITTIER.
.FRIDAY…MOSTLY SUNNY. HIGHS IN THE MID 20S TO LOWER 30S. NORTHWEST
WIND 10 TO 15 MPH IN THE MORNING BECOMING LIGHT. LOCAL GUSTS TO
25 MPH IN THE MORNING NEAR SEWARD AND WHITTIER BECOMING LIGHT.
TEMPERATURE / PRECIPITATION
SEWARD 33 23 30 / 40 0 0
GIRDWOOD 33 19 29 / 40 0 0
This concludes today’s avalanche advisory the next advisory will be on Friday, February 27th. Thanks and have a great day.