Good morning backcountry travelers, this is Lisa Portune with the Chugach National Forest Avalanche Information Center on Sunday, January 18, 2008 at 7am. This will serve as a general backcountry avalanche advisory issued 5 days a week Wednesday through Sunday for the Turnagain Arm area (Turnagain Pass is the core advisory area). Local variations always occur.
Due to warm temperatures and rain at sea level, Placer and 20-Mile are currently closed to motorized use.
MOUNTAIN WEATHER ROUND UP
In the last 24 hours…
-The Center Ridge weather station at 1800 feet in Turnagain Pass is down. Look for this station to be back online soon.
The Grandview weather station at 1100 feet along the railroad tracks recorded no new snow and 0.3 inches of water. The current temperature is 35 degrees F. The freezeline is hovering around 2000 feet and it is currently raining in Girdwood.
-The Sunburst weather station at 3800 feet in Turnagain Pass recorded winds averaging 10-15 mph with gusts in the 20’s out of the East for most of the day yesterday. Max’s weather station at 3200 feet in the Girdwood Valley recorded light winds averaging 5-15 mph with gusts as high as 52 out of the SE. Mountain winds in Turnagain Pass picked up around 1am and are currently averaging 30-40 mph with gusts to 59 out of the East. Ridgetop temps range from 26-29 degrees F.
This past week from Jan 13-16 we got walloped by a pineapple express that delivered over 8 inches of water and 2-5 feet of snow at the mid to higher elevations. Hurricane force easterly winds and torrential downpours at sea level flooded basements and turned roads into skating rinks. All of this followed a 15 day sub-zero cold snap from Dec. 27 to Jan. 10. Thankfully we are looking at some ”normal” weather for a change after a crazy start to the New Year. Expect temps to gradually drop the next few days with rain turning to snow down low. Ridgetop winds will remain strong today averaging 20-45 mph out of the East. We could pick up an additional 12 inches of snow by tomorrow night if we’re lucky.
A Considerable avalanche hazard exists on slopes steeper than 35 degrees above 1800 feet elevation. Use conservative decision making, careful route finding, and good travel habits as unstable slabs are probable on steep terrain.
1. This week’s 2-5 feet of heavy dense storm snow is sitting on a very weak layer of sugary faceted snow and surface hoar that formed during our cold snap. Avalanches triggered on this layer, or stepping down to this layer, will be large and deadly.
2. Sensitive windslab will exist at the higher elevations on leeward westerly aspects near ridgetops, under cornices, and along the sidewalls of subridges in channeled terrain. Visibly drifting snow, shooting cracks, and hollow drum-like hard snow are the most obvious clues to wind slab formation.
AVALANCHE AND SNOWPACK DISCUSSION
Four days of pounding rain, snow, and wind did not “clean out” the snowpack. Yesterday we easily found the January facets buried under the new storm snow above 1800 feet elevation. These facets were still cold and sugary, with the entire weak layer averaging about 1 foot thick. Rain runnels are prominent below 1800 feet where the snowpack is saturated, and once temps cool off to below freezing, these lower elevations will stabilize quickly. This week’s new storm snow should bond together fairly well and quickly because temps were warm and no weak layers had a chance to develop; however, this 2-5 ft. thick slab (and even thicker on windloaded slopes) is sitting on a very significant cold weak layer. This layer had 2 full weeks of cold clear weather to develop and is thus our most dangerous layer of the season so far. Unfortunately it is going to take some time for this layer to strengthen and stabilize.
We saw evidence yesterday of numerous natural avalanches that occurred during the storm, the most obvious one being the entire west face of Magnum (see photo gallery). This large avalanche probably occurred at the end of the storm on Friday. It ran down into the alders and stepped down to the October facets near the ground. We also saw three small class 1 avalanches on our tour up Tincan that were drifted over with snow, and a larger class 2 slide on a SW aspect at 2500 feet that ran down to the Tincan Creek valley floor. Numerous large debris piles were visible on Sunnyside and on Sunburst’s north aspect (see photo gallery)
Except for the recent natural avalanche activity, there were no CNFAIC Staff obvious signs of instability on Tincan yesterday like shooting cracks or whumphing. One of our observers had the thick facet layer settle but not break during her snow stability test. Myself and anCNFAIC Staff observer both got moderate but clean shears on top of the January facets at 2000′ and 2500′ (CTM13Q2@60cm, CTM19Q2@90cm). Ben and I did a Rutschblock test at 3000′ elevation with the facets 5-6 feet below us, but only the surface wind slabs fractured (RB4-5) Despite all of this, everyone chose to stick to low angle slopes knowing that the cold weak faceted layer still existed below.
This concludes today’s advisory; the next advisory will be Wednesday, January 21st. If you are out in the backcountry and have the chance, please send us your observations. Simply click on “Submit a snow observation online” at the top of the advisory page and fill in the blanks. Thanks and have a great day!
The weather forecast for:
WESTERN PRINCE WILLIAM SOUND-
500 AM AKST SUN JAN 18 2009
…STRONG WIND THIS AFTERNOON THROUGH PORTAGE VALLEY AND ALONG
.TODAY…RAIN ALONG THE COAST…TURNING TO SNOW INLAND. SNOW
ACCUMULATION UP TO 2 INCHES INLAND. HIGHS IN THE UPPER 20S TO UPPER
30S. EAST WIND 15 TO 30 MPH. THROUGH PORTAGE VALLEY AND TURNAGAIN
ARM…SOUTHEAST WIND 20 TO 35 MPH INCREASING TO 35 TO 45 MPH IN THE
.TONIGHT…RAIN ALONG THE COAST…TURNING TO SNOW INLAND. SNOW
ACCUMULATION UP TO 5 INCHES INLAND. LOWS IN THE LOWER 20S TO MID
30S…COOLEST INLAND. EAST WIND 10 TO 20 MPH. THROUGH PORTAGE VALLEY
AND TURNAGAIN ARM…EAST WIND 20 TO 35 MPH DECREASING TO 15 TO 20 MPH
.MARTIN LUTHER KING JR DAY…SNOW AND RAIN LIKELY. SNOW ACCUMULATION
UP TO 5 INCHES INLAND. HIGHS IN THE MID 20S TO UPPER 30S…COOLEST
INLAND. VARIABLE WIND TO 10 MPH.
.MONDAY NIGHT…MOSTLY CLOUDY. SCATTERED SNOW SHOWERS. LOWS IN THE
MID TEENS TO LOWER 30S…COOLEST INLAND. VARIABLE WIND TO 10 MPH.
.TUESDAY…PARTLY CLOUDY. HIGHS IN THE LOWER 20S TO MID 30S…COOLEST
INLAND. VARIABLE WIND 10 MPH.
TEMPERATURE / PRECIPITATION
SEWARD 38 35 38 / 100 80 60
GIRDWOOD 31 23 26 / 80 80 60