Turnagain Pass

Good morning backcountry travelers this is Carl Skustad with the Chugach National Forest Avalanche Information Center on Friday December 18th at 7 am. 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

Placer River Drainage will open for snowmachining today at 12 noon. Twentymile remains closed.

WEATHER ROUNDUP

3800′ -Sunburst Wx Station-

Temperatures have dropped from 2 to -11 degrees F with winds averaging 4-6 with gust of 11 out of the SW. Wind look to be increasing.

2400′-Seattle Ridge Wx Station-

Winds have been increasing averaging 3-6 with gust to 10 out of the N

1800′-Center Ridge Wx Station-

Precip: 0 new snow

Total depth of 57 inches, down 3 inches

Temperatures have dropped from 4 to -2.

Frezno Ridge-

Temperature: -9

Winds: averaging 11-13 with gusts to 21 out of the NNW, winds are increasing

Summit Lake-

Temperature: -4.2

Precip: 0 new snow

Total depth of 30 inches

Yesterday (12/17) afternoon’s snow stake totals

Eddies Lot: 4″ new, 12 ” for the week

Motorized Lot: 6″ new, 12 ” for the week

Sunburst Lot: 4″ new, 12 ” for the week

Johnson Pass North Lot: 3″ new, 11″ for the week

Only a trace of new snow in the advisory area last night. The radars show super light snow showers over the Cook Inlet and moderate snow showers heading toward Cordova over PWS. The satellite show partial clearing over the area. The NWS has forecasted wind to increase and become significant today. The chance of snow showers remains over the weekend. Temperatures warming to near 30 by the end of the weekend.

Forecast

WESTERN PRINCE WILLIAM SOUND-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKST FRI DEC 18 2009

…STRONG WIND THROUGH PORTAGE VALLEY AND ALONG TURNAGAIN ARM

SATURDAY…

.TODAY…MOSTLY CLOUDY WITH SCATTERED SNOW SHOWERS. LOCAL SNOW

ACCUMULATIONS AROUND 2 INCHES. AREAS OF BLOWING SNOW IN THE MORNING

NEAR SEWARD AND WHITTIER. HIGHS ZERO TO 15 ABOVE…COLDEST INLAND.

NEAR WHITTIER…WEST WIND 15 TO 25 MPH. GUSTS TO 40 MPH THIS MORNING.

NEAR SEWARD…NORTH WINDS 10 TO 20 MPH. GUSTS TO 30 MPH THIS MORNING.

ELSEWHERE…WEST WINDS 5 TO 15 MPH.

.TONIGHT…CLOUDY WITH A CHANCE OF SNOW AFTER MIDNIGHT. LOWS 10 BELOW

TO 10 ABOVE…COLDEST INLAND. VARIABLE WIND TO 10 MPH.

.SATURDAY…SNOW LIKELY. BLOWING SNOW REDUCING VISIBILITIES TO ONE

HALF MILE AT TIMES ALONG TURNAGAIN ARM AND THROUGH PORTAGE VALLEY.

SNOW ACCUMULATION 2 TO 5 INCHES. HIGHS 15 TO 25. EAST WIND 10 TO 20

MPH EXCEPT EAST 35 TO 45 MPH THROUGH PORTAGE VALLEY AND TURNAGAIN

ARM.

.SATURDAY NIGHT…SNOW LIKELY. AREAS OF BLOWING SNOW. LOWS 10 TO 20

ABOVE. EAST WIND 10 TO 15 MPH. THROUGH PORTAGE VALLEY AND TURNAGAIN

ARM…EAST WIND 15 TO 25 MPH DECREASING TO VARIABLE 10 MPH AFTER

MIDNIGHT.

.SUNDAY…SNOW LIKELY. HIGHS IN THE MID 20S TO LOWER 30S. SOUTHEAST

WIND 15 TO 25 MPH EXCEPT EAST 25 TO 35 MPH THROUGH PORTAGE VALLEY AND

TURNAGAIN ARM.

TEMPERATURE / PRECIPITATION

SEWARD 6 4 23 / 40 20 60

GIRDWOOD 0 -2 16 / 30 20 40

AVALANCHE DISCUSSION

Today’s avalanche danger level will start at LOW and rise to MODERATE if and when winds materealize. Moderate avalanche hazard is described as heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully, identify features of concern. I would go as far as to say areas that are being actively wind loaded by strong winds could see CONSIDERABLE avalanche danger. On those leeward slopes you may see natural avalanches occurring.

If avalanches are triggered today they will be small to moderate in size. The main instability is approximately 12 inches deep. This is the interface of this week’s snow and last week’s surface hoar or wind and sun crusts. A 12 inch deep avalanche is nothing to mess with. This is the small side of the possible depth range. Leeward aspects will see this 12 inch slab increase in depth very rapidly as a result of wind loading.

This week’s snow has had time to settle. This is good and bad. In today’s scenario, it may be bad. The blower light snow we saw this week, is settling into a slab. This means it is actually forming some energy to move as a slab on last week’s snow surface. Last week’s snow included wind and sun affected surfaces above 2000 ft and surface hoar below 2000 ft.

My main area of concern today would be on alpine ridge tops where wind is actively loading leeward aspects. Hanging snow fields and fat new wind slabs forming in couloirs reek of avalanche dragon habitat.

Recent stability test have been showing easy shears on this week/last week’s snow interface.

AnCNFAIC Staff concern today continues to be the glide cracks. Tincan in particular has lots of these crevasse like features which will be hidden due to recent wind. Watch your partners. We had a report of a guy who fell into a four foot glide crack this week.

Always remember that safe backcountry travel requires training and experience. You control your own risk by choosing where, when, and how you travel.

Thanks for checking today’s avalanche advisory. The next one will be posted tomorrow Saturday December 19.