Good Morning backcountry travelers, this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Thursday, March 19, 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-
No major changes since yesterday. The sun was definately the biggest factor as far as snowpack is concerned. Yesterday’s temps stayed below freezing at most weather stations, but the intensity of the sun was strong enough to affect the snow. Portage is the odd ball with temps “yo-yoing” between negative 1 and positive 34 degrees. CNFAIC Staff than that, the weather stations from Summit Lake to Girdwood are reading about the same as yesterday. Winds were light, but are increasing slightly this morning.
–The NRCS Center Ridge weather station at 1800 feet in Turnagain Pass–
Has a temp of 21 degrees (2 degrees warmer than yesterday). Zero new precip, and 4 inches of settlement since the St. Paddy’s storm. Total snowpack depth is 80 inches.
–The Sunburst weather station at 3800 feet in Turnagain Pass–
Is recording a temp of 14 degrees (6 degrees colder than yesterday). Winds were light averaging 2-13 mph with a max gust of 19mph.
-Surface Analysis Maps-
Between 3am and 9pm yesterday….Show a couple of weak low pressures to our east getting weaker as they spin around in some sort of eddy in the Gulf of Alaska. There is also a high pressure to our west building in strength.
Radar shows scattered precip in the Gulf of AK just outside of Prince William Sound. The satellite as of 5am jives with the surface maps from last night.
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.
-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
Normal Caution with pockets of elevated caution is advised today. See the photo in the photo gallery of the Twin Peaks natural avalanche for an idea of what “pockets of elevated caution” means. Class 2 avalanches like the natural we observed on Twin Peaks are still possible for a human to trigger today. An avalanche this size has the potential to bury, injure, or kill a person. Use elevated caution in areas of convuluted terrain and slopes steeper than 38 degrees.
We got a report of a skier-triggered slab that was about 3 feet deep, although it is unclear where this happened. Nobody was caught or injured.
We played it conservative again yesterday and went back to Tincan. Once again, we jumped around on every steep test slope we could find, dug multple hand pits, dug one formal pit, and put in a ski cut on the steep rollover on Hippie Bowl. To sum it up, we have been finding good stability between the old snow/new snow interface. That glazed donut layer is still there and we did find several uneven Q3 shears slightly above that thin freezing rain crust that formed 3/5/09.
We had great visibility so we drove to the Hope Y and pulled out the binocs to look for natural activity. We also looked around from to top of Tincan. The most significant natural avalanche that we saw was on Twin Peaks (see photo gallery). This natural avalanche probably occured on Tuesday after the storm backed off. This is a HUGE piece of the avalanche puzzle. There are no indications of avalanches propogating across entire mountain faces right now, but it is very real and possible for a human to trigger an avalanche the size of the one on Twin Peaks. An avalanche that size is all it takes to bury and kill you especially over terrain traps. Use elevated caution on convuluted terrain and slopes steeper than 38 degrees.
As far as the deep instability with the Janurary Hurricane layer, the ingredients are there for big avalanches, but the balance has not been tipped yet. The question remains…. What is going to tip the balance? We don’t know, and there is a fairly high level of uncertainty with this layer. The trigger for this weak layer might be the sun, maybe it will require rain on snow. Either way the lower elevation slopes in areas like Placer/Skookum and the Seattle Creek bowls are likely areas for this weak layer to be dangerous because these areas have steep slopes below 2800 feet in elevation.
WESTERN PRINCE WILLIAM SOUND-
500 AM AKDT THU MAR 19 2009
.TODAY…MOSTLY CLOUDY WITH ISOLATED SHOWERS. HIGHS IN THE UPPER 20S
TO MID 30S. NORTH AND EAST WIND 5 TO 15 MPH.
.TONIGHT…PARTLY CLOUDY. LOWS IN THE MID TEENS TO LOWER 20S. NORTH
AND WEST WIND 5 TO 15 MPH.
.FRIDAY…MOSTLY SUNNY. HIGHS IN THE MID 20S TO LOWER 30S.
NORTH AND WEST WIND 5 TO 15 MPH.
.FRIDAY NIGHT…MOSTLY CLEAR. LOWS 5 TO 15 ABOVE. NORTH AND WEST WIND
5 TO 15 MPH.
TEMPERATURE / PRECIPITATION
SEWARD 33 22 30 / 0 0 0
GIRDWOOD 35 14 31 / 20 0 0
This concludes today’s avalanche advisory which will expire in 24 hours. The next advisory will be on Friday, March 20th. Thanks and have a great day.