Good morning backcountry travelers, this is Lisa Portune with the Chugach National Forest Avalanche Information Center on Sunday, February 1, 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 NRCS Center Ridge weather station at 1800 feet in Turnagain Pass-
recorded no new snow. The current temp is 5F with a total snowpack depth of 65 inches.
-The Sunburst weather station at 3800 feet in Turnagain Pass-
recorded winds averaging 10-15 mph out of the East with gusts in the 20’s.
-Max’s weather station at 3200 feet in the Girdwood Valley-
recorded winds averaging 5-10 mph out of the SE and East with gusts in the teens and 20’s.
-General Weather Observations-
As of 4:00 am this morning, mountain temperatures were in the single digits F with light winds blowing 5-10 mph out of the N and W, except at 43 Mile Peak where they were blowing 15-20 mph out of the N. Today, a weak low pressure system in the gulf will influence our weather. 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 cloudy skies will produce some scattered snow showers this morning with skies clearing by afternoon.
Primary avalanche concerns
-Surface wind slabs above treeline
AVALANCHE AND SNOWPACK DISCUSSION
This week 6-10 inches of snow fell in Turnagain Pass and the Girdwood Valley. Localized strong winds blew this low-density new snow into 2-12 inch windslabs above treeline on a variety of aspects. Most of these windslabs are small, soft, manageable slabs that will fracture right under your skis, board, or sled. At the higher elevations closer to the ridgetops, thicker windslabs exist. On Thursday, Matt intentionally triggered a soft windslab on the north side of Tincan at 3900 feet. This slab was up to 12 inches deep and 50 feet wide and ran 1000 feet down Todd’s Run. Ski cuts are very effective with these new soft slabs if you know how to do them safely. The main hazard would be unexpectedly triggering one above steep complex terrain. Harder, drum-like slabs also exist, especially at the higher elevations above 3000 feet. These are the ones to look out for because they are not manageable and will fracture unexpectedly above you.
Yesterday, 12 of our observers braved the sunny skies and blower powder all in the name of science. A BIG thank you goes out to the Friends of the CNFAIC and all of our observers for their valuable time and energy! Carl’s group on Tincan found pockets of 12 inch deep soft slab with 20 ft. shooting cracks near the ridgetops above 3500 feet. Ben triggered a 6 inch deep, 75 ft. wide surface soft slab on a steep convex rollover at 3100 feet on a SW aspect. I also triggered a small soft shallow wind slab on a convex rollover on Sunburst. These slides were easy to ski through and pretty much harmless. Matt’s group checked out the back bowls on the motorized side and found good stable skiing that was more protected from the winds.
On long steep unsupported slopes, especially those approaching 40 degrees or steeper, it is certainly possible to trigger loose snow avalanches. These sluffs may be large enough to catch and carry a person in steep terrain, and they can pile up fairly deep if given a chance to run.
On slopes below 2800 feet elevation, the new snow is sitting on a thick crust that formed during our mega-meltdown two weeks ago. Right now this is not much of a concern because the new snow is so light. Once we get more of a load, however, the crust will be an excellent bed surface for future avalanches.
Deep slab instabilities may exist at the higher elevations above 3000 feet where temps are colder and the facets remain weak and sugary. An unlikely, but outside chance remains of triggering a deep slab avalanche in thin, rocky starting zones in these higher elevations.
This concludes today’s advisory; the next advisory will be Wednesday, February 4th. 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 1 2009
.TODAY…MOSTLY CLOUDY IN THE MORNING THEN BECOMING PARTLY
CLOUDY. ISOLATED SNOW SHOWERS EXCEPT LIGHT SNOW NEAR PORTAGE IN THE
MORNING. SNOW ACCUMULATION UP TO 2 INCHES. HIGHS 10 TO 20 ABOVE.
NORTHWEST WIND 10 TO 15 MPH EXCEPT NORTH TO WEST 20 TO 35 MPH NEAR
SEWARD AND WHITTIER.
.TONIGHT…PARTLY CLOUDY. LOWS 5 BELOW TO 15 ABOVE…COOLEST
INLAND. NORTHWEST WIND 10 TO 15 MPH EXCEPT NORTH TO WEST 15 TO 30 MPH
NEAR SEWARD AND WHITTIER.
.MONDAY…PARTLY CLOUDY IN THE MORNING THEN BECOMING MOSTLY
CLOUDY. SCATTERED SNOW SHOWERS. HIGHS 5 TO 15 ABOVE. NORTHWEST
WIND 10 TO 15 MPH EXCEPT NORTH 15 TO 25 MPH NEAR SEWARD. WIND
CHILLS 5 BELOW TO 20 BELOW IN THE MORNING.
.MONDAY NIGHT…MOSTLY CLOUDY IN THE EVENING THEN BECOMING PARTLY
CLOUDY. LOWS 10 BELOW TO 10 ABOVE…COOLEST INLAND. NORTHWEST
WIND 10 TO 15 MPH EXCEPT NORTH 15 TO 25 MPH NEAR SEWARD.
.TUESDAY…PARTLY CLOUDY. HIGHS 5 TO 15 ABOVE. VARIABLE WIND TO 10
TEMPERATURE / PRECIPITATION
SEWARD 19 5 13 / 20 0 0
GIRDWOOD 13 -2 9 / 20 0 40