Good morning backcountry travelers this is Lisa Portune with the Chugach National Forest Avalanche Information Center on Sunday, March 14th at 7am. This will serve as a general backcountry avalanche advisory issued for Turnagain Arm with Turnagain Pass as the core advisory area (this advisory does not apply to highways, railroads, or operating ski areas).
The weather has been fairly quiet this past week after Monday’s big storm dumped 30-40 inches in 24 hours. Yesterday skies were sunny in the afternoon while mountain temperatures warmed up to the mid teens to upper 20’s. Ridgetop winds averaged 10-20mph out of the east on Sunburst but were light and variable on Seattle Ridge. Two inches of new snow fell last night in Turnagain Pass and three inches fell in Grandview and the Girdwood Valley. As of 4am this morning, ridgetop winds are averaging 5-10mph out of the northeast and temperatures range from 14F at 3800 feet to 20F at sea level. We could get 7-12 inches of additional snow at the higher elevations today and tonight as a frontal system moves across southcentral. Snowfall will vary in intensity as bands of precip spin off the low in the gulf. Ridgetop winds will increase to 15-25mph out of the east today while mountain temperatures will warm up to the mid to upper 20’s.
Today the avalanche danger is rated MODERATE with pockets of CONSIDERABLE hazard developing later today on windloaded slopes greater than 35 degrees. A sun crust formed yesterday on southerly aspects and is now being buried under the new snow. Sensitive windslab will be our primary concern today, especially on leeward southerly aspects where the buried sun crust will act as a slick bed surface. AnCNFAIC Staff concern is higher elevation windswept aspects where the snowpack remains shallow and weak. Human-triggered avalanches are possible near rock outcrops and scoured ridges where older weak layers are closer to the surface and thus more easily impacted by skis, boards, or snowmachines. A large skier-triggered avalanche happened three days ago on such a slope.
Skiers and riders have been out in force hitting big lines the last three days without incident. The one glaring exception was the large skier-triggered avalanche this past Thursday on the south face of Cornbiscuit. This large avalanche was triggered near some exposed rocks on the high point of the ridge while the group was skinning. The slope had already been skied 7-10 times that day with no obvious signs of instability observed. It propagated 300-500 feet wide and ran 1500 feet down and 100 ft. up the north side of Lipps. The crown face ranged from 1 foot deep at the trigger point to 6 feet deep in the windloaded areas. It failed on a 1-3 cm thick crust with small facets. Some thoughts on this slide…Although it was over 48 hours after the big storm, below zero temperatures at the higher elevations may have caused instabilities to linger longer than usual. It caught a lot of people by surprise. If you dig a snowpit, use your probe to find shallow areas of the snowpack to test where crust/facet layers may be more reactive. Three to four feet deep total snowpack depth is ideal.
We received a report of a natural avalanche yesterday on Kickstep around 4:30pm. It’s unclear whether this was sluffing from solar radiation or windslab from strong winds. The group also reported 1-8 inch thick windslab on top of softer snow while booting up the west ridge as well as moderate sluffing running the length of the face.
I will issue the next advisory tomorrow morning at 7am. If you get out in the backcountry give us a call at 754-2369 or send us your observations using the button at the top of this page. Thanks and have a great day.
The NWS weather forecast for:
WESTERN PRINCE WILLIAM SOUND-
500 AM AKDT SUN MAR 14 2010
.TODAY…SNOW. SNOW ACCUMULATION 2 TO 6 INCHES. HIGHS IN THE 30S.
NEAR WHITTIER…WEST WIND 25 TO 35 MPH DIMINISHING TO VARIABLE 15 MPH
BY AFTERNOON. NEAR SEWARD…NORTH WIND 30 MPH DECREASING TO 15 MPH IN
THE AFTERNOON. NORTH WIND 10 TO 15 MPH ELSEWHERE.
.TONIGHT…SNOW LIKELY. SNOW ACCUMULATION UP TO 4 INCHES. LOWS IN
THE MID 20S TO LOWER 30S. NORTHEAST WIND 10 TO 15 MPH.
.MONDAY…NUMEROUS SNOW SHOWERS IN THE MORNING…THEN SCATTERED
SNOW SHOWERS IN THE AFTERNOON. SNOW ACCUMULATION UP TO 2 INCHES.
HIGHS IN THE MID 30S TO LOWER 40S. NORTHEAST WIND 10 TO 15 MPH.
.MONDAY NIGHT…MOSTLY CLOUDY. LOWS IN THE MID 20S TO LOWER 30S.
VARIABLE WIND 10 MPH.
TEMPERATURE / PRECIPITATION
SEWARD 35 28 40 / 90 70 80
GIRDWOOD 34 28 37 / 80 60 60
WEATHER STATION SUMMARY for Turnagain Pass:
-3800′ Sunburst Wx Station-
recorded light to moderate winds yesterday averaging 10-20mph out of the east with gusts to 30mph. The current temp is 14F (6 degrees warmer than yesterday) with winds averaging 5-10mph out of the northeast.
-2600′ Seattle Ridge Wx Station-
recorded light and variable winds yesterday. Winds are currently averaging 2mph out of the north.
-1800′ Center Ridge Wx Station-
recorded 2 inches of new snow in the last 24 hours. The current temp is 15F (1 degree warmer than yesterday) with a total snowpack depth of 128 inches.