Good morning backcountry travelers this is Lisa Portune with the Chugach National Forest Avalanche Information Center on Sunday, April 4th 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).
Skookum Valley and Skookum Glacier are closed to motorized vehicles (snowmachines, helicopters, ATVs) except for subsistence uses. This closure is directed in the current Chugach National Forest Land and Resource Management Plan. Placer River Drainage remains open for motorized use to Spencer Glacier.
Wow, what an incredible spring day we had yesterday! Sunny skies, light and variable winds, and afternoon temperatures in the mid 30’s to mid 40’s made it feel downright tropical for us sun-starved Alaskans. It stayed above 40F at the Center Ridge weather station from noon to 5pm yesterday. Our last significant snowfall was four days ago when Turnagain Pass got 20 inches of snow and 1.8 inches of water. As of 4am this morning, temperatures range from 36F@sealevel to 30F@1800′ to 22F@3800′. Skies are mostly cloudy right now, and ridgetop winds are averaging 10-15 mph out of the east. The main weather feature today will be the strong to gale force easterly winds associated with a gulf low. Ridgetop winds will increase as the day progresses, averaging 25-45mph and possibly higher by this afternoon. Turnagain Pass may see up to 6 inches of new snow by tomorrow morning if we’re lucky while mountain temperatures will warm up to the low to mid 20’s at the higher elevations and push 40 degrees at the mid elevations.
Today the avalanche danger is rated MODERATE overall with pockets of CONSIDERABLE hazard developing later today on steep upper elevation windloaded slopes greater than 35 degrees. Today’s strong winds will easily transport northerly powder to slick sun-crusted southerly aspects creating pockets of fresh windslab near the ridgetops. Human-triggered avalanches will be likely on any actively loading slopes. Of equal concern today are the multiple layers of buried surface hoar that formed last month in the top four feet of the snowpack. Buried surface hoar on shaded northerly aspects was responsible for several human triggered avalanches a week ago that fractured 2-3 feet deep. Avalanches triggered on or stepping down to these layers have the potential to go big.
Fortunately no human-triggered avalanches were reported yesterday, but there was one notable close call. Several glide cracks avalanched yesterday afternoon in Turnagain Pass in the heat of the day…one on the south face of Shark Fin and the CNFAIC Staff one on Sunnyside just above the snowmachine uptrack (see photo below). I turned around just in time to watch the flowing debris stop short of covering the main track. Scary stuff. Luckily no one was caught. Stay out from under those things, especially on hot sunny days.
Jon and I toured up Magnum yesterday and found a layer of buried surface hoar 2 feet down on a north aspect at 2400 feet. We got clean fast Q1 shears on this layer, a huge heads-up and an obvious sign of instability. We decided not to ride the steep powdery north chute because of what we found in our snowpit and instead took the low angle route down. On the flip side, many folks skied steep northerly aspects the last few days without triggering anything. The buried surface hoar is pockety, so make sure to dig down and evaluate each slope individually before diving in. Also of note yesterday, an explosive-triggered avalanche (2 lb. charge) on a north aspect in the Girdwood Valley broke 3 feet deep and stepped down an additional 3 feet to a deeper unknown weak layer.
Natural avalanche activity the last few days has been caused by daytime heating and intense sunshine. We mostly saw wet snow point releases on southerly aspects. However, two full-depth natural wet slabs avalanched in the upper Girdwood Valley at 2000 feet elevation on Thursday and Friday. Yesterday, Alex saw a very recent less-than-24-hour-old full-depth avalanche on a southeast aspect at mile 6 of the Hope Highway. This one was 150 feet wide by 600 feet long. He also saw a 600 ft. wide recent natural on a southwest aspect of Moose Pk. in the Summit Lake area that stepped down to deeper weak layers. These are all reminders to get off of south aspects on hot sunny afternoons.
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 APR 4 2010
…STRONG WIND THROUGH TONIGHT THROUGH PORTAGE VALLEY AND
ALONG TURNAGAIN ARM…
.TODAY…NUMEROUS SNOW SHOWERS IN THE MORNING…THEN NUMEROUS
RAIN AND SNOW SHOWERS IN THE AFTERNOON. SNOW ACCUMULATION
UP TO 2 INCHES. HIGHS IN THE UPPER 30S TO MID 40S. EAST WIND
10 TO 15 MPH INCREASING TO 15 TO 30 MPH IN THE AFTERNOON. THROUGH
PORTAGE VALLEY AND TURNAGAIN ARM…EAST WIND 30 TO 45 MPH.
.TONIGHT…RAIN AND SNOW IN THE EVENING…THEN SNOW LIKELY AFTER
MIDNIGHT. SNOW ACCUMULATION UP TO 4 INCHES. LOWS IN THE MID 20S
TO LOWER 30S. EAST WIND 20 TO 35 MPH EXCEPT EAST 35 TO 50 MPH
THROUGH PORTAGE VALLEY AND TURNAGAIN ARM.
.MONDAY…SNOW LIKELY IN THE MORNING…THEN RAIN AND SNOW LIKELY
IN THE AFTERNOON. SNOW ACCUMULATION UP TO 3 INCHES. HIGHS IN THE
MID 30S TO LOWER 40S. EAST WIND 10 TO 25 MPH EXCEPT EAST 25 TO
40 MPH THROUGH PORTAGE VALLEY AND TURNAGAIN ARM.
TEMPERATURE / PRECIPITATION
SEWARD 45 31 40 / 70 80 60
GIRDWOOD 44 26 38 / 50 50 60
WEATHER STATION SUMMARY for Turnagain Pass:
-3800′ Sunburst Wx Station-
recorded light westerly winds yesterday averaging 1-5mph. The high temp yesterday was 47F at 4pm. The current temp is 22F with winds averaging 10-15mph out of the east.
-2600′ Seattle Ridge Wx Station-
recorded light and variable winds yesterday averaging 1-10mph. The high temp yesterday was 35F at 11am. The current temp is 26F with winds averaging 15-20mph out of the southeast.
-1800′ Center Ridge Wx Station-
recorded no new snow in the last 24 hours. The high temp yesterday was 44F at 2pm. The current temp is 30F with a total snowpack depth of 138 inches (3 inches of settlement/melting in the last 24 hours).