Good morning backcountry travelers this is Lisa Portune with the Chugach National Forest Avalanche Information Center on Sunday, January 23rd 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 avalanche danger rating remains at MODERATE this morning but will increase to CONSIDERABLE later today if we get the high-end estimate of 11 inches of new snow the NWS is forecasting for the higher elevations. The east winds are already starting to ramp up this morning and are expected to hit gale force by mid day. At the least we’ll see POCKETS OF CONSIDERABLE hazard today due to windloading. The winds, coupled with almost a foot of new snow, will most certainly create dangerous avalanche conditions in the backcountry. If this storm pans out, human-triggered avalanches will be likely on windloaded terrain with long running fractures possible.
Our primary concern right now is the new snow/old snow interface. The 4-6 inches of new snow that fell over the past four days buried some formidable weak layers…the most notable being the widespread surface hoar that formed during the 2 week cold snap January 5-18. The new snow also buried wind crusts, hard windslab, exposed ice crusts, and sugary faceted snow….all poor bonding surfaces for the light density snow that fell this past week. No doubt about it, anCNFAIC Staff foot of snow and gale force winds will equal dicey avalanche conditions.
This past Thursday skiers were able to trigger some highly reactive soft slabs in the upper Girdwood Valley. The slabs were no more than a foot deep, but one propagated over 130 feet wide and failed on the buried surface hoar. Every ski cut they performed resulted in a small avalanche, and even their dog triggered a 20 ft. wide slab on a small roll. They stuck to manageable terrain and avoided deeper windloaded areas. I think this was a small preview of things to come once we get a decent snow load in Turnagain Pass.
Our deeper slab instabilities are now a secondary concern. It has been two weeks since the last reported human-triggered avalanche on one of these layers. These persistent weak layers consist of buried surface hoar that formed in December and facets above and below the Thanksgiving Rain Crust. Although they have seemingly lost their reactivity, a slim chance always remains of triggering an avalanche on one of these layers. We’ll probably see some avalanches stepping down to these deeper layers during our next big avalanche cycle.
Encyclopedia of terms: www.fsavalanche.org/Encyclopedia.aspx
No new snow fell in the last 24 hours in Turnagain Pass. Under cloudy skies yesterday, winds were light with mountain temperatures in the teens to mid 20’s. Ridgetop winds started to increase early this morning and are currently averaging 15-30mph out of the east gusting to 50. A strong front will bring gale-force easterly winds today with possibly up to a foot of new snow above 1000 feet. We’ll see temperatures climb to the mid to upper 20’s at the higher elevations and upper 30’s at sea level.
I will issue my last 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 AKST SUN JAN 23 2011
…STRONG WIND THROUGH TONIGHT…
.TODAY…SNOW…MIXED AT TIMES WITH RAIN. AREAS OF BLOWING SNOW
INLAND WITH VISIBILITIES REDUCED TO ONE HALF MILE AT TIMES. SNOW
ACCUMULATIONS 2 TO 6 INCHES…HIGHEST INLAND AND AT HIGHER
ELEVATIONS. HIGHS IN THE LOWER 30S TO LOWER 40S. NORTH TO EAST WINDS
INCREASING TO 15 TO 30 MPH WITH LOCAL GUSTS TO 45 MPH. THROUGH
PORTAGE VALLEY AND TURNAGAIN ARM…EAST WINDS 25 TO 45 MPH WITH GUSTS
TO 60 MPH BY AFTERNOON.
.TONIGHT…SNOW AND RAIN. SNOW ACCUMULATION UP TO 5 INCHES. LOWS
IN THE LOWER TO MID 30S. SOUTH TO EAST WINDS 15 TO 30 MPH WITH LOCAL
GUSTS TO 45 MPH DECREASING TO 10 TO 25 MPH AFTER MIDNIGHT. THROUGH
PORTAGE VALLEY AND TURNAGAIN ARM…EAST WIND 30 TO 45 MPH WITH GUSTS
TO 60 MPH DIMINISHING 20 TO 40 MPH AFTER MIDNIGHT.
.MONDAY…RAIN AND SNOW IN THE MORNING…THEN A CHANCE OF RAIN AND
SNOW IN THE AFTERNOON. SNOW ACCUMULATION UP TO 1 INCH. HIGHS IN THE
LOWER TO MID 30S. SOUTHEAST WIND 10 TO 20 MPH. THROUGH PORTAGE VALLEY
AND TURNAGAIN ARM…EAST WIND 30 TO 40 MPH DECREASING TO 15 TO 20 MPH
IN THE AFTERNOON.
TEMPERATURE / PRECIPITATION
SEWARD 36 35 35 / 80 80 80
GIRDWOOD 40 31 33 / 60 70 70
WEATHER STATION SUMMARY for Turnagain Pass:
-3800′ Sunburst Wx Station-
recorded light winds averaging 5-10mph out of the northwest yesterday and temps ranging from 13F to 22F. The winds picked up last night and are now averaging 15-20mph out of the NE. Temp is currently 17F.
-2600′ Seattle Ridge Wx Station-
recorded light and variable winds yesterday with temps ranging from 17F to 25F. The winds picked up last night and are now averaging 20-30mph out of the SE. Temp is currently 21F.
-1800′ Center Ridge Wx Station-
recorded no new snow in the last 24 hours. Temps yesterday ranged from 18F to 27F. The current temp is 26F.