Good Morning backcountry travelers, this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Friday, March 20, 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 expires in 24 hours and does not apply to operating ski resorts or highways/railroads.
MOUNTAIN WEATHER ROUND UP FOR THE LAST 24 HOURS
-General Weather Observations-
Temps made it above freezing to about 2000 feet yesterday for the first time during this bluebird session; however, the temps are colder by 2-14 degrees compared to yesterday morning. The warmest part of the day according the the weather stations from Summit to Girdwood is generally between 3-5pm. Winds have been light to moderate on ridges, just enough of a breeze to keep things cool.
–The NRCS Center Ridge weather station at 1800 feet in Turnagain Pass–
Has a temp of 12 degrees (9 degrees colder than yesterday). Zero new precip, and a total of 6 inches of settlement since the St. Paddy’s storm. Total snowpack depth is 78 inches.
–The Sunburst weather station at 3800 feet in Turnagain Pass–
Is recording a temp of 9 degrees (5 degrees colder than yesterday). Winds were mostly light averaging 3-15 mph with a max gust of 23mph.
-Surface Analysis Maps-
Between 3am and 9pm yesterday….Show lots of high pressure to our west.
Clear. Nothing remarkable for our location.
Primary avalanche concerns
-Below 3000 feet. The “Janurary Hurricane” rain crust buried under 2-5 feet of surface snow. There is a layer of weak sugary faceted snow on top and below this hard rain crust. Stability tests on this layer continue to show clean fast Q1 shears on top of this rain crust. This weak layer is still showing signs of life, and probably will become very dangerous if it gets any sort of rapid load, especially rain and rapid warming from intense sun.
-Sea-level up to at least 3800 feet (Probably higher). The thin “glazed donut” freezing rain crust that formed 3/5/09 has been observed throughout the Turnagain Arm area. This layer formed almost everywhere on all aspects from the parking lots to the ridgetops. This layer is now buried under about 2 feet of snow
AVALANCHES AND SNOWPACK
Generally normal caution “low” with pockets of elevated caution “moderate” is advised today. See the photo in the photo gallery of the Twin Peaks natural avalanche for an idea of what I mean by “pockets of elevated caution”. There is anCNFAIC Staff photo of a skier-triggered from 3/18/09 avalanche that shows anCNFAIC Staff example of one of these isolated pockets. An avalanche this size has the potential to bury, injure, or kill a person. The most likely areas for a human to trigger these pockets will be on slopes steeper than 38 degrees on complicated terrain.
We got anCNFAIC Staff report of skier-triggered slab avalanche 2 feet deep and 20 feet wide at 3500 feet on Corbiscuit ridge near Superbowl that occured 3/18/09. A well respected skier mentioned that he is “Leary of steep lines with big exposure.” Those are great words to live by today.
Travel is generally safe right now, but we have one major problem. Those isolated pockets out there are big enough to bury, injure, or kill a person; so, we can’t take those pockets lightly. Unfortunately, these isolated pockets are possible on all aspects partly due to that “glazed donut” rain crust. Stability tests have been showing a pattern of an uneven failure a couple inches above this crust. If you get a case of the “ooga-boogas” before dropping into something, then you should listen to those gut instincts today and scale your slope angles back.
The new snow that fell just before St. Patrick’s Day has settled 6 inches, which means it has turned into more of a cohesive slab. So what does that mean? Well, either it means stability has improved because the entire slope is going to stick together better, or we are setting up for slab avalanches when the hot sun to warms up the surface snow causing it to creep down slope. There is a little bit of a question mark there; so, to be on the safe side watch out for intense sun and if temps make it above freezing up at higher elevations. Direct southern aspects will be the most likely spot for this situation. So far, temps have remained cool up high with a slight breeze. The sun has still been effecting the snow causing numerous sun sluffs from Girdwood to Summit, but none of these point releases has triggered any remarkable slab avalanches. If you start seeing these sluffs triggering slabs, then its time to head back to the parking lots.
Here’s my latest thoughts on the January Hurricane layer…
We know that it is confined to lower elevations. Thats why we are concerned about the steep slopes in places like Placer/Skookum, Seattle Creek, and Kern/Peterson, because those slopes start at sea-level instead of 1000 feet like they do at Turnagain Pass. Eventually something is going to tip the balance with this weak layer. Now that it is getting warm and sunny, I’m starting to get nervous about direct southern aspects on steep slopes at lower elevations. So we need to be aware of temps staying above freezing for prolonged amounts of time. The CNFAIC Staff big possibilty for triggering this deep instability will be rain on snow; so, watch out when that happens.
And for the future, we have been seeing surface hoar growing rapidly all over the place.
WESTERN PRINCE WILLIAM SOUND-
500 AM AKDT FRI MAR 20 2009
.TODAY…MOSTLY SUNNY. HIGHS IN THE MID 20S TO LOWER 30S.
NORTH TO WEST WIND TO 15 MPH EXCEPT STRONGER WINDS TO 25 MPH NEAR
SEWARD AND WHITTIER.
.TONIGHT…MOSTLY CLEAR. LOWS 5 TO 15 ABOVE EXCEPT 5 BELOW TO
5 ABOVE INLAND. VARIABLE WIND 10 MPH EXCEPT NORTH 20 MPH NEAR
SEWARD AND WEST WIND TO 25 MPH NEAR WHITTIER.
.SATURDAY…PARTLY CLOUDY IN THE MORNING THEN BECOMING MOSTLY
CLOUDY. HIGHS IN THE 20S. VARIABLE WIND TO 10 MPH. NEAR
SEWARD…NORTH WIND 10 TO 15 MPH.
TEMPERATURE / PRECIPITATION
SEWARD 31 17 26 / 0 0 0
GIRDWOOD 27 11 25 / 0 0 0
This concludes today’s avalanche advisory which will expire in 24 hours. The next advisory will be on Saturday, March 21st. Thanks and have a great day.