Good morning backcountry travelers this is Lisa Portune with the Chugach National Forest Avalanche Information Center on Sunday, February 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).
Yesterday a snowmachiner triggered a large avalanche on the west ridge of Grandview at approximately mile 43 of the railroad tracks between Portage and Moose Pass. Two riders were caught and buried, one was killed, and one is still missing. We have very limited information at this time. AnCNFAIC Staff avalanche off of Hiland Road north of Anchorage buried and killed a skier yesterday as well. Our sympathies and condolences go out to their family and friends.
Under partly cloudy skies yesterday, ridgetop winds averaged 10-20mph out of the east while mountain temps were in the mid 20’s to low 30’s. AnCNFAIC Staff 2 inches of new snow fell last night in Turnagain Pass, bringing our snowfall total for the last 9 days to around 4 feet of snow and 4 inches of water. Actual amounts vary with the southern end of the pass getting half that much snow and greater amounts falling at the upper elevations. It is currently raining at sea level and snowing above 1500 feet, with temps ranging from 25F at 3800 feet to 33F at sea level. Ridgetop winds have already started to ramp up ahead of the next low, averaging 30mph out of the east with gusts in the 40’s. AnCNFAIC Staff strong gulf low will impact us today, tonight, and tomorrow bringing gale to storm force easterly winds, rain at sea level, and up to 12 inches of new snow at the higher elevations.
The avalanche danger will rise to CONSIDERABLE today with pockets of HIGH hazard later this afternoon as this storm progresses. Human-triggered avalanches will be likely on steep windloaded slopes with natural avalanches possible on actively loading westerly aspects. Some of these avalanches may step down into deeper weak layers making very large and dangerous avalanches. We pretty much hit the tipping point the last few days, and this next storm will just add more stress to a snowpack with significant buried weak layers. Yesterday was the dangerous trifecta of 3-day weekend, bluebird day following a storm, and great powder. Two snowmachiners were buried in a large avalanche near Grandview, with one killed and one still missing.
We have some tricky instabilities in the snowpack right now, most notably several layers of buried surface hoar that formed in January and early February. Numerous natural and human-triggered avalanches failed on buried surface hoar layers this past week on leeward westerly aspects, including one that partially buried a skier last Saturday on Tincan. The entire southwest face of Pete’s North ripped out on a layer of small buried surface hoar 2-3 days ago. And I suspect the three medium sized natural avalanches that happened on Friday on Tincan’s northwest aspect failed on buried surface hoar layers as well (see photo gallery). We’re finding these feathery crystals buried anywhere from 1.5 to 3.5 feet deep up to 3000 feet elevation on both sides of the highway. In some areas the buried surface hoar sits on top of a crust, an especially dangerous combination. The Grandview avalanche yesterday most likely failed on this surface hoar/crust combo. Traveling collapses and whumphing were also reported as recently as yesterday in the Summit Lake area, an obvious sign of instability.
The beefy January 7 rain crust finally reared its ugly head in the upper Girdwood Valley 2 days ago when a small hand charge triggered a large avalanche on this layer. The fracture propagated over 1000 feet wide and broke 4-5 feet deep. New snow avalanches could easily step down to this deep weak layer today, creating a huge and most likely unsurvivable avalanche.
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.
The NWS weather forecast for:
WESTERN PRINCE WILLIAM SOUND-
500 AM AKST SUN FEB 14 2010
…STRONG WIND THIS AFTERNOON THROUGH MONDAY MORNING THROUGH PORTAGE
VALLEY AND TURNAGAIN ARM…
.TODAY…RAIN…MIXED WITH SNOW AT TIMES IN THE MORNING. SNOW
ACCUMULATION UP TO 1 INCH. HIGHS IN THE MID 30S TO LOWER 40S. NORTH
TO EAST WIND 10 TO 15 MPH INCREASING TO 15 TO 30 MPH IN THE
AFTERNOON. THROUGH PORTAGE VALLEY AND TURNAGAIN ARM…EAST WIND 15
TO 30 MPH INCREASING TO 30 TO 45 MPH IN THE AFTERNOON.
.TONIGHT…RAIN SHOWERS…HEAVY AT TIMES. LOWS IN THE MID 30S. EAST
WIND 20 TO 40 MPH EXCEPT EAST 45 TO 65 MPH THROUGH PORTAGE VALLEY
AND TURNAGAIN ARM.
.PRESIDENTS DAY…RAIN AND SNOW SHOWERS…HEAVY AT TIMES IN THE
MORNING. SNOW ACCUMULATION UP TO 3 INCHES. HIGHS IN THE MID 30S TO
LOWER 40S. SOUTH TO EAST WIND 20 TO 35 MPH. THROUGH PORTAGE VALLEY
AND TURNAGAIN ARM…EAST WIND 40 TO 55 MPH DECREASING TO 30 TO 40
MPH IN THE AFTERNOON.
TEMPERATURE / PRECIPITATION
SEWARD 42 36 40 / 100 100 100
GIRDWOOD 37 35 37 / 100 100 100
WEATHER STATION SUMMARY for Turnagain Pass:
-3800′ Sunburst Wx Station-
recorded light to moderate easterly winds yesterday averaging 10-20mph with gusts to 33mph. The current temp is 25F (2 degrees warmer than yesterday) with winds averaging 30mph out of the east.
-2600′ Seattle Ridge Wx Station-
is not working.
-1800′ Center Ridge Wx Station-
recorded 2 inches of new snow and 0.2 inches of water in the last 24 hours. The current temp is 31F (3 degrees warmer than yesterday) with a total snowpack depth of 90 inches.