Good morning backcountry travelers, this is Lisa Portune with the Chugach National Forest Avalanche Information Center on Sunday, February 8, 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.
MOUNTAIN WEATHER ROUND UP
In the last 24 hours…
-The DOT weather station near the crest of the highway in Turnagain Pass at 1000 feet-
is recording a current temp of 3F (2 degrees colder than yesterday) with calm winds.
-The NRCS Center Ridge weather station at 1800 feet in Turnagain Pass-
recorded no new snow. The current temp is 4F with a total snowpack depth of 63 inches.
-The Sunburst weather station at 3800 feet in Turnagain Pass-
recorded light winds averaging 5-10 mph out of the NW with gusts in the teens all day yesterday. The current temp is 5F (7 degrees colder than yesterday)
-General Weather Observations-
Early this morning, ridgetop temperatures were in the single digits F with light winds blowing 5-10 mph out of the NW, except at 43 Mile Peak where they were blowing 10-20 mph out of the NW. Portage is currently 0F, Girdwood 10F, and Summit Lake -10F. Today, mountain temperatures will remain in the single digits, and northwesterly ridgetop winds will blow 10-15 mph with stronger winds closer to the coast. Mostly clear skies and continued cool temps are on tap for the next two days with patchy fog down low.
Primary avalanche concerns
-Wind slabs on a hard dense bed surface above 2800 feet
Secondary avalanche concerns
-Consolidated soft slab and denser wind slab sitting on a rain crust below 2800ft
AVALANCHE AND SNOWPACK DISCUSSION
Human triggered avalanches are possible today on slopes steeper than 38 degrees. Natural avalanches are unlikely. Pockets of sensitive wind slab up to 12 inches deep exist near ridgetops and along crossloaded gullies on all aspects. Ski cuts are very effective with these soft slabs if you know how to do them safely. The main hazard would be unexpectedly triggering one above steep complex terrain and getting caught. At the lower elevations instabilities also exist, especially from 800-1500′ where numerous small skier triggered avalanches occurred this past week on the buried January rain crust.
This week 1-2 inches of snow fell in Turnagain Pass and 5-7 inches fell in the Girdwood Valley. This snow was deposited on 12-18 inches of light density snow that fell the last 2 weeks of January. Localized strong winds this past Tuesday and Thursday created 6-12 inch thick windslabs above treeline on a variety of leeward aspects. In areas that were not wind-affected, all of this light density snow is consolidating and settling into more of a slab. Instead of just sluffing away on steep slopes, this slab is now producing fractures.
All of this snow is sitting on a slippery bed surface that formed during the mid-January pineapple express. Above 2800 feet, this bed surface is a hard dense slab of snow. Below 2800 feet, a thick rain crust surrounded by weak facets exists 10-16 inches below the surface. In my snowpit stability tests yesterday these facets produced easy to moderate clean Q2 shears above and below the crusts. A majority of the skier triggered avalanches this past week ran on this January layer on slopes steeper than 38 degrees. Most of these slides were either intentionally triggered or so small that the person skied right through the slab; however, the ones triggered high on the ridgetops with long steep runouts entrained quite a bit of snow as they ran to the flats below…certainly enough to injure or bury a person.
Here’s a recap of the most recent slides in Turnagain Pass(check out the photo gallery for pics of these slides):
-Skier caught in a shallow slide and carried over some rocks on the backside of Superbowl Peak (Goldpan) at 3700′. It was triggered between rock outcroppings on a 40ish degree slope. The slide was 50 feet wide, 6 inches deep, and ran 150 feet. The skier was not buried and is OK.
-1 small skier-triggered soft slab on the south face of Cornbiscuit at approx. 3000 feet.
-2 small skier-triggered soft slabs on the east face of Sunnyside above the snowmachine uptrack at approx. 1800 feet.
-2 skier triggered wind slabs on the west face of Lipps at 3200 and 2800 feet. The largest of these slides ran 1000 feet to the flats below and pulled out an additional surface slab below some rocks halfway down. The crown face averaged 1 to 1.5 feet deep. The lower slide appeared to have stepped down to anCNFAIC Staff weak layer. These were intentional ski cuts and no one was caught.
-1 small skier triggered windslab at 1500 feet on the east face of Sunnyside across from the Sunburst parking lot. This failed within recently deposited wind layers.
-Skier triggered wind slab on south aspect of Tincan Proper at 3900 feet. This 12″ deep wind slab ran the whole length of the slope for 2000 feet sending debris onto the lower valley flats. The skier was able to ski off the slab and was not caught.
-Skier triggered wind slab on the south face of Eddies near the ridgetop (unknown elevation)
– Skier triggered soft slab on SW aspect of Tincan at 3100 feet. This 6 inch deep x 75 ft. wide surface soft slab was triggered on a steep convex rollover.
-Skier triggered windslab on north side of Tincan (Todd’s Run) at 3900 feet. This slide was 12 inches deep, 50 feet wide, and ran 1000 feet down the slope. This was an intentional ski cut and no one was caught.
Use good travel habits above steep complex terrain, especially on runs that roll to angles pushing 40 degrees or steeper. Have escape routes planned and avoid skiing above cliff bands or terrain traps where the consequences of a slide are greater.
This concludes today’s advisory; the next advisory will be Wednesday, February 11th. 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 FEB 8 2009
.TODAY…MOSTLY SUNNY. HIGHS 15 TO 25. NORTHWEST WIND 10 TO
15 MPH EXCEPT NORTHWEST 20 TO 30 MPH NEAR SEWARD AND WHITTIER.
.TONIGHT…MOSTLY CLEAR. LOWS 5 TO 20 ABOVE…COOLEST INLAND.
VARIABLE WIND TO 10 MPH. NEAR SEWARD…NORTHWEST WIND 15 TO 25 MPH
DECREASING TO 10 MPH AFTER MIDNIGHT.
.MONDAY…PARTLY CLOUDY IN THE MORNING THEN BECOMING MOSTLY
CLOUDY. SCATTERED SNOW SHOWERS. HIGHS 15 TO 25. LIGHT WINDS.
.MONDAY NIGHT…MOSTLY CLOUDY IN THE EVENING THEN BECOMING PARTLY
CLOUDY. SCATTERED SNOW SHOWERS. LOWS 10 TO 20 ABOVE. VARIABLE WIND TO
.TUESDAY…PARTLY CLOUDY IN THE MORNING THEN BECOMING MOSTLY
CLOUDY. HIGHS IN THE LOWER TO MID 20S. VARIABLE WIND TO 10 MPH. NEAR
SEWARD…NORTH WIND 10 MPH.
TEMPERATURE / PRECIPITATION
SEWARD 23 11 22 / 0 0 40