Good Morning backcountry travelers, this is Carl Skustad with the Chugach National Forest Avalanche Information Center on Saturday, January 31, 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.
MOUNTAIN WEATHER ROUND UP
In the last 24 hours…
-General Weather Observations-
Temperatures have cooled off again this morning with many single digits being reported. Winds picked up yesterday afternoon around the Girdwood Valley and was actively transporting snow, less wind was reported in Turnagain Pass. In the past 4 days we have received 4-6 inches of new snow. Snow showers are forecasted for the area.
–The DOT weather station near the crest the highway at Turnagain Pass at 1000 feet–
Is recording a temp of 9 degrees (13 degrees cooler than yesterday), calm winds averaging 2 mph from the west.
–The NRCS Center Ridge weather station at 1800 feet in Turnagain Pass–
Has a temp of 3 degrees (16 degrees cooler than yesterday). It looks like we received approx. 3-4 ” of new snow in the last 24 hours and .2″ of water equivalent. Total snowpack depth is 64″.
–The Sunburst weather station at 3800 feet in Turnagain Pass–
Is showing increasing winds with gust from 21-32 out of the east. The temperature is 0 deg F.
-Surface Analysis Maps-
The 990 mb low responsible for or current snow activity is slowly spinning out of Prince William Sound to the east.
The radar images are not showing a lot of precip activity on tap for us today. These very light snow showers do not show up very good on the radar as I realized yesterday.
Primary avalanche concerns
-Surface wind slabs on alpine ridges
AVALANCHE AND SNOWPACK
Below Tree line the avalanche hazard is low, normal caution is advised. Keep in mind if the wind snuck into small glades or onto terrain features you will find small wind slabs.
Above treeline we have a slightly increased avalanche hazard. Natural wind slab avalanches are possible and human triggered avalanches are probable on leeward aspects were wind is actively transporting snow. These pockets of increased avalanche potential hold 2-12 inch wind slabs. Most of the snow you find today will be light and fluffy, no problem. If you find snow that is stiffer and drum like you have found a wind slab. If the angle of your new found wind slab is greater than 35 degrees it will avalanche and zoom down the hill. Most of these are harmless but the larger wind slabs you could find near ridge tops would be dangerous if you unexpectedly triggered one and it carried you over complex terrain like cliff bands or into terrain traps.
On Thursday we intentionally triggered multiple small windslabs on Tincan Ridge. Most of the south aspect windslabs were small, 2 to 10 inches, and were being actively formed from northerly winds. The north facing aspects held deeper wind slabs from Tuesdays winds. The notable wind slab we released ran 1000 feet down Todd’s Run. This slab was 2 to 12 inches deep and 50 ft wide. Triggering small avalanches from cornices or wind slabs can work as good slope stability tests. Advanced experience is required.
Tincan Ridge, notice the northerly winds actively loading the south faces
We dug a pit at 3800 ft (refigured my elevation) and found all the weak layers from the season. None of them were that responsive. CT scores in the mid 20’s to 30 plus. We found January facets and even October facets and surface hoar. We haven’t heard of any easy test results on any weak layers in over a month. No human triggered avalanches have been reported. My discussion is not the green light for everything. You will find varying conditions above tree line and I am sure you could find avalanches that could ruin your day on complex alpine terrain. Localized winds will be important to watch.
A wind slab we kicked loose ran from 3800 ft to 2700 ft, see the toe of the debris down in the bowl
WESTERN PRINCE WILLIAM SOUND-
500 AM AKST SAT JAN 31 2009
.TODAY…SNOW SHOWERS IN THE MORNING NORTH OF MOOSE PASS WITH
ADDITIONAL SNOW ACCUMULATION UP TO 1 INCH. CNFAIC StaffWISE…MOSTLY CLOUDY
WITH SCATTERED SNOW SHOWERS. HIGHS 10 TO 20 ABOVE. NORTHWEST WIND
10 TO 15 MPH BECOMING VARIABLE IN THE AFTERNOON. NEAR
SEWARD…NORTH WIND 20 TO 30 MPH DECREASING TO 15 MPH IN THE
.TONIGHT…MOSTLY CLOUDY WITH SCATTERED SNOW SHOWERS. LOWS ZERO
TO 15 ABOVE…COOLEST INLAND. NORTH TO WEST WIND 10 TO 15 MPH.
.SUNDAY…MOSTLY CLOUDY WITH SCATTERED SNOW SHOWERS. HIGHS 15 TO
25 ABOVE…COOLEST INLAND. NORTH TO WEST WIND 5 TO 15 MPH. GUSTS TO
25 MPH NEAR SEWARD AND WHITTIER.
.SUNDAY NIGHT…PARTLY CLOUDY. LOWS 5 BELOW TO 15 ABOVE…COOLEST
INLAND. NORTHWEST WIND 10 TO 25 MPH.
.MONDAY…PARTLY TO MOSTLY CLOUDY WITH ISOLATED SNOW SHOWERS. HIGHS
10 TO 20 ABOVE. NORTHWEST WIND 10 TO 25 MPH.
TEMPERATURE / PRECIPITATION
SEWARD 18 12 20 / 40 40 40
GIRDWOOD 14 3 15 / 80 20 20
This concludes today’s avalanche advisory the next advisory will be on Sunday, February 1st. Thanks and have a great day.