Turnagain Pass

Good morning backcountry travelers this is Lisa Portune with the Chugach National Forest Avalanche Information Center on Monday, January 24th 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).

BOTTOM LINE

The avalanche danger rating remains at CONSIDERABLE today. Yesterday’s storm dropped 9 inches of new snow accompanied by gale force easterly winds. An additional 5 inches of snow is possible for the higher elevations today along with continued strong winds. Human-triggered avalanches will be likely today on windloaded terrain with long running fractures possible.

AVALANCHE DISCUSSION

Numerous folks reported dicey avalanche conditions yesterday in Turnagain Pass as the storm ramped up in intensity. Bad visibility kept most everyone out of the higher elevations, so most observations came from treeline and below. By late afternoon, skiers were able to trigger some highly reactive soft slabs on small windloaded test slopes. One broke 20 inches deep and propagated over 80 feet wide. I suspect many of these avalanches failed on the large layer of buried surface hoar that formed during our 2 week cold snap. Remember that surface hoar is famous for producing long running fractures that pull back onto mellow slope angles, so be extremely cognizant of the terrain around you.

A total of 12-16 inches of upside-down snow has fallen over the past five days burying some significant weak layers…the most notable being the widespread surface hoar that formed January 5-18. This new snow also buried wind crusts, hard windslab, exposed ice crusts, and sugary faceted snow….all poor bonding surfaces for the lighter density snow that fell first. While only 0.7 inches of water weight was added to the snowpack yesterday, keep in mind that windloaded slopes at the higher elevations probably have over twice that amount and that avalanches up to 2 feet deep are possible.

Our deeper slab instabilities remain a secondary concern, but a concern nonetheless, especially now that we’re getting new snow. These persistent weak layers consist of buried surface hoar that formed in December and facets above and below the Thanksgiving Rain Crust. Although it has been two weeks since the last reported human-triggered avalanche on one of these layers, the weight and added energy of our new snowfall has the potential to ‘reactivate’ these layers. Avalanches triggered today could certainly step down to one of these deeper layers as well, creating a much larger avalanche.

Encyclopedia of terms: www.fsavalanche.org/Encyclopedia.aspx

WEATHER ROUNDUP

Yesterday’s storm dropped 9 inches of new snow at Turnagain Pass (finally!) accompanied by gale force easterly winds. Mountain temperatures warmed up to the mid to upper 20’s while the rain line hovered around 500 feet elevation. The winds backed off last night but are still averaging 20-25mph out of the east this morning. Temps currently range from 40F at sea level to 26F at 3800 feet. Predicted snowfall amounts are all over the board right now for the next 24 hours, so I’ll make an educated guess of 5 inches at the higher elevations in the next 12 hours. We’ll see. Expect continued strong winds today out of the east, rain below 1000 feet, and mountain temps in the upper 20’s to mid 30’s.

Jon 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:

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKST MON JAN 24 2011

…STRONG WINDS TONIGHT THROUGH PORTAGE VALLEY AND ALONG TURNAGAIN

ARM…

.TODAY…RAIN MIXED AT TIMES WITH SNOW. LITTLE SNOW ACCUMULATION.

HIGHS IN THE MID 30S TO LOWER 40S. SOUTH TO EAST WINDS 15 TO 30 MPH

DIMINISHING 10 TO 20 MPH THIS AFTERNOON. THROUGH PORTAGE VALLEY AND

TURNAGAIN ARM…EAST WIND 30 MPH…WITH GUSTS TO 40 MPH THIS MORNING.

.TONIGHT…RAIN AND SNOW SHOWERS LIKELY. SNOW ACCUMULATION 1 TO 3

INCHES. LOWS IN THE LOWER 20S TO LOWER 30S. NORTH TO EAST WINDS 15 TO

30 MPH. THROUGH PORTAGE VALLEY AND TURNAGAIN ARM…EAST WINDS 35 TO

50 MPH.

.TUESDAY…RAIN AND SNOW IN THE MORNING…THEN A CHANCE OF SNOW AND

RAIN IN THE AFTERNOON. SNOW ACCUMULATION UP TO 5 INCHES. HIGHS IN THE

UPPER 20S TO MID 30S. EAST WIND 20 TO 35 MPH BECOMING SOUTHEAST 10 TO

15 MPH IN THE AFTERNOON. THROUGH PORTAGE VALLEY AND TURNAGAIN ARM…

EAST WIND 35 TO 45 MPH DECREASING TO 20 TO 35 MPH IN THE AFTERNOON.

TEMPERATURE / PRECIPITATION

SEWARD 40 26 33 / 80 70 80

GIRDWOOD 36 29 31 / 70 60 70

WEATHER STATION SUMMARY for Turnagain Pass:

-3800′ Sunburst Wx Station-

recorded gale-force winds yesterday averaging 30-55mph gusting to 78 out of the NE. Temps increased from 19F to 25F during the day. The winds decreased last night but are still averaging 20mph out of the NE. Temp is currently 25F.

-2600′ Seattle Ridge Wx Station-

recorded strong to gale-force winds yesterday averaging 30-45mph gusting to 67 out of the SE. Temps increased from 22F to 28F during the day. The winds backed off just a bit last night but are still averaging 20-25mph out of the SE. Temp is currently 29F.

-1800′ Center Ridge Wx Station-

recorded 9 inches of new snow and 0.7 inches of water in the last 24 hours. Temps yesterday increased from 28F to 31F during the day. The current temp is 32F.