Turnagain Pass

Good morning backcountry travelers this is Lisa Portune with the Chugach National Forest Avalanche Information Center on Sunday, March 21st 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).

ANNOUNCEMENTS

Telepalooza & Alyeska World Comp March 23-28. Check out details at www.telepalooza.com. The event will have Telemark demos, lessons, races, beacon park games, and a raffle. The raffle has HUGE prizes with all proceeds going to the Friends of the Chugach National Forest Avalanche Center. See you there!

WEATHER ROUNDUP

The first day of Spring was a beauty yesterday…sunshine, warm temps, and light winds made for a great day in the mountains. Yesterday temperatures started off in the low to mid 20’s and warmed up to the low 40’s at 1800 feet, low 30’s at 2400 feet, and mid 20’s at 3800 feet. Winds averaged 5-10mph out of the east while skies were mostly sunny. Temperatures are a bit cooler this morning than this time yesterday, ranging from 18F@sea level to 23F@1800′ to 22F@3800′. Skies are currently clear while ridgetop winds are light and variable. AnCNFAIC Staff gorgeous spring day is on tap as high pressure dominates.

AVALANCHE DISCUSSION

The avalanche danger will rise to CONSIDERABLE this afternoon on steep sunny slopes. Natural and human-triggered slides are likely. Watch for indicators such as pinwheels, rollerballs, and point-release sluffs. These sluffs may gouge into the snowpack and cause slab avalanches on deeper weak layers. Human-triggered slab avalanches are also possible on sun baked slopes where the snowpack is thin and rocky and on shaded aspects where a layer of surface hoar is now buried under 1 to 1.5 feet of snow. We have several layers of buried sun crusts and facets that were reactive to human triggers this past week. Don’t overstay your welcome on steep southerly terrain today.

A few small natural slab avalanches happened yesterday afternoon up at the pass in addition to wet sluffs on steep southerly aspects. Jon saw several new wet slabs on southeast facing Sunnyside near sun-warmed rocky outcrops while I noticed a new soft slab avalanche on a west aspect of Pete’s North at 2000 feet that happened sometime between 11am and 4pm (see photo gallery).

Many new natural avalanches happened this past Friday after Thursday’s storm dumped 12-18 inches of new snow in Turnagain Pass. Most were small to medium sized slab avalanches on south and west aspects that were triggered by falling cornice chunks or wet sluffs. The biggest one was on the west facing headwall of Eddies (see photo below). The crown face was 1 to 3 feet deep and 450 feet wide, and the failure layer was the new snow/old snow interface (no crust). Thursday’s snow fell on a one inch thick sun crust that formed March 15-17 on south through southwest aspects. We got clean shears on this layer yesterday at 3300 feet on Tincan (CTM13,14Q2). A layer of surface hoar also formed March 15-17 on all aspects up to the ridgetops, so be careful if you venture onto more northerly aspects looking for softer snow.

Our most recent human-triggered avalanches occurred this past Tuesday March 16 when the weather was warm and sunny. These slides had several things in common…shallow trigger points on steep southerly aspects, propagation into deeper snow, and failure on buried crusts with small facets. All were triggered in the afternoon when the sun and temperatures were at their warmest.

When it snows again, our next weak link will be the current snow surface. A 1 inch thick breakable melt-freeze/rain crust extends up to 2000 feet elevation on all aspects and makes for some extra challenging skiing and riding conditions. Survival skiing at its finest. Just to keep us on our toes, a new batch of surface hoar is forming up to 2700 feet in addition to anCNFAIC Staff sun crust on southerly slopes.

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:

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKDT SUN MAR 21 2010

.TODAY…SKIES BECOMING MOSTLY CLOUDY. ISOLATED RAIN AND SNOW SHOWERS

IN THE AFTERNOON. HIGHS IN THE MID 30S TO LOWER 40S. LIGHT WINDS.

.TONIGHT…MOSTLY CLOUDY WITH A CHANCE OF SNOW SHOWERS. LOWS IN THE

LOWER 20S TO LOWER 30S. VARIABLE WINDS 5 TO 15 MPH.

.MONDAY…MOSTLY CLOUDY. A CHANCE OF SNOW SHOWERS IN THE

MORNING…THEN A CHANCE OF SNOW AND RAIN SHOWERS IN THE

AFTERNOON. HIGHS IN THE MID 30S TO LOWER 40S. VARIABLE WINDS 5 TO 15

MPH.

TEMPERATURE / PRECIPITATION

SEWARD 42 28 38 / 20 40 40

GIRDWOOD 41 25 38 / 0 20 40

WEATHER STATION SUMMARY for Turnagain Pass:

-3800′ Sunburst Wx Station-

recorded light winds yesterday averaging 5-10mph out of the east. The current temp is 22F (1 degree colder than this time yesterday) with winds averaging 1mph out of the northeast.

-2600′ Seattle Ridge Wx Station-

recorded light winds yesterday averaging 5-10mph out of the southeast. The current temp is 23F (2 degrees colder than this time yesterday) with winds averaging 4mph out of the northeast.

-1800′ Center Ridge Wx Station-

recorded no new snow in the last 24 hours. The current temp is 23F (3 degrees colder than this time yesterday) with a total snowpack depth of 132 inches (3 inches of settlement since yesterday).