Good morning backcountry travelers this is Lisa Portune with the Chugach National Forest Avalanche Information Center on Sunday, April 11th 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.
No new snow fell in the last 24 hours in Turnagain Pass. Under greybird skies yesterday, southeasterly ridgetop winds averaged 5-10mph on Sunburst and 15-20mph on Seattle Ridge. Mountain temperatures warmed up yesterday to the high 20’s at the upper elevations and 40F at the mid elevations. It is currently snowing lightly at sea level in Girdwood as of 4am this morning. The winds increased a bit last night and are currently averaging 15mph on Sunburst and 20mph on Seattle Ridge while temperatures this morning range from 20F@3800′ to 29F@1800′ to 35F@sealevel. The front associated with a large stacked low will bring widespread precip to our area today. We could get anywhere from 6-13 inches of new snow today and tonight at the higher elevations with a rain/snow mix at sealevel. Ridgetop winds will be moderate to strong today, averaging 15-30mph out of the east, while mountain temperatures will warm up to the mid 20’s to low 30’s.
Today the avalanche danger is rated MODERATE overall with pockets of CONSIDERABLE hazard developing later today on steep windloaded slopes greater than 35 degrees. If this storm comes in with a bit more punch, you will likely trigger new snow sluffs and shallow windslabs on steep slopes by this afternoon. Natural avalanches will also be possible on any actively loading slopes above treeline as well. Today’s new and wind-transported snow will bury a recently formed layer of surface hoar in addition to a slick suncrust on E-S-W aspects. An outside chance also remains of triggering a deeper slab avalanche in thin, rocky starting zones in the upper elevations.
Today’s new snow will bury a sizeable layer of surface hoar that formed this past Thursday and Friday. The crystals grew larger at the higher elevations, ranging from ¼ inch at 2500 feet to ½ inch at 4300 feet. On E-S-W aspects the surface hoar is sitting on a suncrust, an especially dicey combination. Jon and I noticed that yesterday’s high overcast skies kept the surface hoar from melting on southerly aspects.
No human-triggered avalanches were reported yesterday. One of our regular observers reported intentionally ski-cutting several recently formed windslabs in the north-facing chutes on Pete’s North on Friday. The largest one ran 900 feet and was 40 feet wide by 1.5 feet deep. AnCNFAIC Staff one of our regular observers reported finding 2 separate layers of buried surface hoar 3 ft. and 4 ft. down in the snowpack on a northeast aspect of Pastoral at 4400 feet. Compression tests showed that the layers had lost their reactivity on that particular slope (CTH25,28,29,30++,all Q2’s). Yesterday Jon and I toured up KoRnbiscuit and found a layer of buried surface hoar 1.5 feet deep in one of the north facing chutes at 3200 feet. We got full propagation across the column during 3 separate Extended Column Tests (ECTP12,15,27), so we backed off of riding that enticing line. On the flipside, many steep north facing lines were skied the last few days with no problems. Like we said before, the numerous layers of buried surface hoar that formed last month are highly variable in their distribution and sensitivity over aspect and elevation. Make sure to dig down and evaluate each individual slope before committing to a line.
Three glide cracks avalanched yesterday: a large one on the south face of Eddies (see photo below), one on the south side of Shark Fin, and one on a west facing slope in the Skookum Valley. That makes six glide cracks that have avalanched this past week. Everywhere I look there seems to be a new glide crack forming. Lucky for us, these things are easily avoidable. They have their own agenda so stay out from under them.
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 11 2010
.TODAY…SNOW…MIXING WITH OR CHANGING TO RAIN NEAR SEA LEVEL.
SNOW ACCUMULATION UP TO 4 INCHES. HIGHS IN THE 30S. SOUTH TO EAST
WIND 15 TO 30 MPH WITH GUSTS TO 40 MPH THROUGH PORTAGE VALLEY
AND TURNAGAIN ARM.
.TONIGHT…RAIN AND SNOW. SNOW ACCUMULATION UP TO 4 INCHES.
LOWS IN THE 30S. SOUTH TO EAST WIND 15 TO 30 MPH WITH GUSTS
TO 40 MPH THROUGH PORTAGE VALLEY AND TURNAGAIN ARM…DECREASING
TO 10 TO 20 MPH AFTER MIDNIGHT.
.MONDAY…SNOW AND RAIN LIKELY IN THE MORNING…THEN A SLIGHT
CHANCE OF RAIN AND SNOW SHOWERS IN THE AFTERNOON. SNOW ACCUMULATION
UP TO 1 INCH. HIGHS AROUND 40. VARIABLE WIND 10 MPH EXCEPT
SOUTHEAST 15 TO 25 MPH THROUGH PORTAGE VALLEY AND TURNAGAIN ARM.
TEMPERATURE / PRECIPITATION
SEWARD 38 33 41 / 100 100 50
GIRDWOOD 37 32 40 / 100 100 80
WEATHER STATION SUMMARY for Turnagain Pass:
-3800′ Sunburst Wx Station-
recorded light southeasterly winds yesterday averaging 5-10mph. The high temp yesterday was 27F at 3pm. The current temp is 20F with winds averaging 15mph out of the east.
-2600′ Seattle Ridge Wx Station-
recorded moderate southeasterly winds yesterday averaging 15-20mph with gusts to 28mph. The high temp yesterday was 26F at 1pm. The current temp is 24F with winds averaging 20mph out of the southeast.
-1800′ Center Ridge Wx Station-
recorded no new snow in the last 24 hours. The high temp yesterday was 39F at 1pm. The current temp is 29F with a total snowpack depth of 141 inches (2 inches of settlement/melting in the last 24 hours).