Turnagain Pass

Good morning backcountry travelers this is Jon Gellings with the Chugach National Forest Avalanche Information Center on Tuesday, December 14th 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

Today the avalanche hazard will remain MODERATE overall. Natural avalanches are unlikely, but small human triggered avalanches are possible in steep terrain in upper elevation areas, where we have 3 different layers of surface hoar buried above the Thanksgiving Rain Crust. If one of these layers fails and starts sliding, the possibility exists for layers further down in the snowpack to be affected and fail as well.

AVALANCHE DISCUSSION

A few days ago, we received a report of a small skier triggered avalanche somewhere in the Magnum/Cornbiscuit area. Although the windslab which failed was only 6 inches deep, it entrained a comparatively large amount of snow on the way down. No investigation has taken place, but it seems more likely that the weak layer which failed was one of the surface hoar layers buried above the Thanksgiving Rain Crust. The surface hoar layers formed from the valley bottoms to the ridgetops nearly everywhere in Turnagain Pass and were covered up by small amounts of snow here and there over the last week. For the most part the deepest layer a few inches above Thanksgiving crust seems to have lost most of its reactivity, and the newer layers in non wind-affected terrain are buried between new snow layers of equal density and are not buried deep enough yet to be a problem. If the winds pick up, remember that surface hoar tends to survive lower on slopes in wind-protected areas than near windswept ridges, so be prepared for buried pockets midslope and always have an escape route.

On anCNFAIC Staff issue, the Thanksgiving Rain Crust is continuing to show signs of the faceting process both above and below it. There are many varying observations coming in, but the overall trend is decreasing strength with low energy. It is currently buried at all elevations and aspects, and is between 4 inches and 1.5 feet deep. Collapses, as well as no failures are observed in random terrain areas when doing stability tests. As of right now, no avalanches have been reported that have broken down to this layer, but it is definitely a persistent instability of concern. In its current state, it will need a much bigger snow load before it starts becoming a major concern in most areas.

WEATHER ROUNDUP

Yesterdays skies started off fairly unobstructed, but soon became more and more cloudy. The Girdwood valley received a thick cloud bank last night, and it is currently still with us at 6 am. Yesterday, the winds were light out of the northwest, while mountain temperatures dropped into the single digits and low teens. Our inversion has corrected itself, which has left the alpine several degrees colder than the valley bottoms. Expect fog down low this morning giving way to high clouds this afternoon from a weak low pressure in the gulf. Winds should remain on the light side except near Whittier where west winds are forecasted to be between 35-50mph. Keep this in mind if you decide to head to Portage Valley today or tomorrow.

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-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKST TUE DEC 14 2010

…STRONG WIND THROUGH THURSDAY NEAR WHITTIER…

.TODAY…NUMEROUS SNOW SHOWERS IN THE MORNING…BECOMING PARTLY

CLOUDY IN THE AFTERNOON. HIGHS 10 TO 20 ABOVE…COOLEST INLAND.

NORTHWEST WIND 10 TO 15 MPH EXCEPT NORTH 25 TO 40 MPH NEAR SEWARD.

NEAR WHITTIER…WEST WIND 35 TO 50 MPH WITH GUSTS TO 65 MPH NEAR

WHITTIER.

.TONIGHT…PARTLY CLOUDY. LOWS ZERO TO 15 BELOW. NORTHWEST WIND

10 TO 25 MPH EXCEPT NORTH 30 TO 40 MPH NEAR SEWARD. NEAR

WHITTIER…WEST WIND 35 TO 50 MPH WITH GUSTS TO 65 MPH.

.WEDNESDAY…MOSTLY SUNNY. HIGHS 5 BELOW TO 15 ABOVE. NORTHWEST

WIND 10 TO 20 MPH EXCEPT NORTH 25 TO 40 MPH NEAR SEWARD. NEAR

WHITTIER…WEST WIND 35 TO 50 MPH WITH GUSTS TO 65 MPH.

TEMPERATURE / PRECIPITATION

SEWARD 17 -7 11 / 40 0 0

GIRDWOOD 13 -2 0 / 60 0 0

WEATHER STATION SUMMARY for Turnagain Pass:

-3800′ Sunburst Wx Station-

recorded light northwest winds yesterday averaging 5-9mph and temps dropping from 15F to 9F. The current temp is a balmy 5F with light winds out of the north.

-2600′ Seattle Ridge Wx Station-

recorded light north winds yesterday averaging 2-7mph, with temps dropping from 17F to 8F. The current temp is 9F with light winds out of the northwest.

-1800′ Center Ridge Wx Station-

recorded no new snow, and 1″ of settlement in the last 24 hours. Temps yesterday increased from 6F to 13F, but then started dropping again. The current temp is 10F with a total snowpack depth of 53 inches.