Good morning backcountry travelers this is Lisa Portune with the Chugach National Forest Avalanche Information Center on Monday, February 8th 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).
AnCNFAIC Staff 3 inches of new snow fell in the last 24 hours in Turnagain Pass, bringing our snowfall total for the last 2 ½ days to around 16 inches of snow and 1.2 inches of water. Most of this snow fell Friday night through Saturday morning and was accompanied by strong easterly winds. Yesterday ridgetop winds were light, averaging 5-15mph out of the east, while mountain temps were in the mid teens to low 20’s. As of 4am this morning, temps range from 8F at 3800 feet to 23F at sea level. Ridgetop winds are currently light out of the north while sea level winds are averaging 20mph. A brief spell of high pressure will bring partly cloudy skies today before we get walloped by a big storm tonight and tomorrow. Expect cooler mountain temps in the single digits and teens today with light ridgetop winds.
Today the avalanche danger is rated MODERATE, which means that human-triggered avalanches are possible on windloaded slopes steeper than 35 degrees. Natural avalanches are unlikely today. The new storm snow from this past weekend has lost most of its energy, but I would still approach big steep unsupported slopes with caution. Evaluate the snow and terrain carefully before jumping in, especially windloaded rollovers and crossloaded gullies where pockets of buried surface hoar and/or sensitive windslab may still be lingering and reactive to a human trigger. We have several different layers of buried surface hoar that formed in January that are highly variable over elevation and terrain in regard to size and sensitivity. That, combined with slabby surface snow, means human triggered avalanches are possible.
Matt and I toured up Tincan yesterday to take a closer look at the avalanche that partially buried a skier on Saturday at 3000 feet on a southwest aspect. On our way up, we noticed a new skier-triggered slide at 2600 feet on a northwest aspect that looked similar in size to the CNFAIC Staff avalanche…150 feet wide, 200 feet long, 1 to 1.5 feet deep at the crown face. I’m guessing this slide happened late in the day on Saturday as well. Both of these avalanches failed underneath recently formed windslabs on a very small layer of buried surface hoar sitting on top of a thin melt-freeze crust. The wind was actively loading these leeward slopes on Saturday which added a significant amount of energy to the snowpack at that time. Once the wind stopped, the snowpack was able to gradually adjust to its new load and become less reactive over time. Matt and I stomped on and ski cut several 38-40 degree slopes next to the slides yesterday and got no signs of instability. Regardless, we stuck to simple manageable terrain and agreed that we would not feel comfortable skiing big open steep slopes. One of our observers reported finding windslabs up to 1 ft. thick on Sunburst that failed easily during his snowpit tests but no CNFAIC Staff signs of instability. His group stuck to the lower angle west aspect of Sunburst where the snow was not as wind affected.
None of the recent avalanche activity at the pass stepped down to the buried Jan. 7 rain crust, now buried 2-4 feet deep and even deeper on leeward aspects. It’s certainly possible, however, that a big enough avalanche could easily step down to this persistent weak layer and create an even bigger slide, especially on the northern end of the pass where we found buried surface hoar lurking on top of this slick crust and clean fast Q1 shears in our stability tests.
Always remember that safe backcountry travel requires training and experience. You control your own risk by choosing where, when, and how you travel.
Matt 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 MON FEB 8 2010
…STRONG WIND TONIGHT THROUGH TUESDAY AFTERNOON THROUGH PORTAGE
VALLEY AND TURNAGAIN ARM…
.TODAY…BECOMING PARTLY CLOUDY. AREAS OF BLOWING SNOW NEAR WHITTIER
IN THE MORNING. HIGHS IN THE MID TEENS TO LOWER 30S. LIGHT WINDS.
NEAR WHITTIER…WEST WIND 30 MPH BECOMING BECOMING VARIABLE 10 MPH IN
.TONIGHT…SNOW. SNOW ACCUMULATION 3 TO 7 INCHES. AREAS OF BLOWING
SNOW WILL REDUCE VISIBILITIES TO LESS THAN A MILE THROUGH PORTAGE
VALLEY AND TURNAGAIN ARM. NEAR STEADY TEMPERATURES IN THE MID TEENS
TO LOWER 30S…COLDEST INLAND. NORTH TO EAST WIND 10 TO 20 MPH
INCREASING TO 20 TO 30 MPH AFTER MIDNIGHT. THROUGH PORTAGE VALLEY
AND TURNAGAIN ARM…EAST WIND 25 TO 40 MPH INCREASING TO 40 TO
55 MPH AFTER MIDNIGHT.
.TUESDAY…SNOW IN THE MORNING…THEN SNOW AND RAIN IN THE
AFTERNOON. SNOW ACCUMULATION UP TO 6 INCHES. AREAS OF BLOWING SNOW
WILL REDUCE VISIBILITIES TO LESS THAN A MILE THROUGH PORTAGE VALLEY
AND TURNAGAIN ARM IN THE MORNING. HIGHS IN THE 30S. NORTH TO EAST
WIND 20 TO 30 MPH EXCEPT SOUTHEAST 45 TO 60 MPH THROUGH PORTAGE
VALLEY AND TURNAGAIN ARM.
TEMPERATURE / PRECIPITATION
SEWARD 24 24 38 / 0 100 80
GIRDWOOD 26 26 33 / 0 80 80
WEATHER STATION SUMMARY for Turnagain Pass:
-3800′ Sunburst Wx Station-
recorded light easterly winds yesterday averaging 5-15mph with gusts in the 20’s. The current temp is 8F (5 degrees colder than yesterday) with winds averaging 3mph out of the northwest.
-2600′ Seattle Ridge Wx Station-
recorded light southeasterly winds yesterday averaging 5-15mph with gusts in the 20’s. Winds are currently averaging 4mph out of the north.
-1800′ Center Ridge Wx Station-
recorded 3 inches of new snow and 0.1 inches of water in the last 24 hours. The current temp is 15F (3 degrees colder than yesterday) with a total snowpack depth of 72 inches.