Turnagain Pass

Good morning backcountry travelers this is Carl Skustad with the Chugach National Forest Avalanche Information Center on Saturday December 19th 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 is open to snowmachineing. Twentymile remains closed.

WEATHER ROUNDUP

3800′ -Sunburst Wx Station-

Temperatures have risen from -11 to 2 degrees F with winds averaging 10-19 with gust of 29 out of the SE. Winds look to be increasing.

2400′-Seattle Ridge Wx Station-

Winds have been increasing averaging 18 with gust to 24 out of the SE

1800′-Center Ridge Wx Station-

Precip: 0 new snow

Total depth of 57 inches

Temperatures have have risen from -2 to 10.

Fresno Ridge-

Temperature: -9

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

Summit Lake-

Temperature: 3 degrees F

Precip: 0 new snow

Total depth of 28 inches

(12/17) weekly snow stake totals:

Eddies Lot: 12 ” for the week

Motorized Lot: 12 ” for the week

Sunburst Lot: 12 ” for the week

Johnson Pass North Lot: 11″ for the week

No snowfall overnight in the advisory area. The radar and satellite images show substantial precipitation moving our direction. However, the rotation of flow on the Prince William Sound radar has it heading north. We will see if it spins west into our area. The NWS is forecasting a Blizzard warning for this afternoon. Temperatures and winds have picked up in all areas. Ridge top winds are gusting near 30 mph. A 990 mb low in sliding up the cost and should be in our area later today.

Forecast

WESTERN PRINCE WILLIAM SOUND-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKST SAT DEC 19 2009

…BLIZZARD WARNING IN EFFECT FROM NOON TODAY TO 10 PM AKST THIS

EVENING FOR PORTAGE VALLEY ALONG TURNAGAIN ARM…

.TODAY…SNOW DEVELOPING THIS MORNING. AREAS OF BLOWING SNOW.

VISIBILITIES WILL BE REDUCED TO ONE QUARTER MILE OR LESS AT TIMES IN

BLOWING SNOW IN PORTAGE VALLEY AND TURNAGAIN ARM. SNOW ACCUMULATION 4

TO 10 INCHES. HIGHS 15 TO 25. NORTH TO EAST WINDS 10 TO 25 MPH.

THROUGH PORTAGE VALLEY AND TURNAGAIN ARM…EAST WIND 20 TO 30 MPH

INCREASING TO 35 TO 50 MPH IN THE AFTERNOON.

.TONIGHT…SNOW AND BLOWING SNOW. VISIBILITIES OCCASIONALLY REDUCED

TO ONE QUARTER MILE OR LESS IN BLOWING SNOW IN PORTAGE VALLEY AND

ALONG TURNAGAIN ARM IN THE EVENING. SNOW ACCUMULATION 3 TO 8 INCHES.

LOWS 15 TO 25. EAST WIND 10 TO 25 MPH. THROUGH PORTAGE VALLEY AND

TURNAGAIN ARM…EAST WIND 30 TO 50 MPH DECREASING TO 15 MPH BY

MIDNIGHT.

.SUNDAY…SNOW LIKELY IN THE MORNING BECOMING MIXED WITH RAIN IN THE

AFTERNOON. AREAS OF BLOWING SNOW. SNOW ACCUMULATION 1 TO 4 INCHES.

HIGHS AROUND 30. SOUTHEAST WIND 15 TO 30 MPH EXCEPT EAST 30 TO 45 MPH

THROUGH PORTAGE VALLEY AND TURNAGAIN ARM.

.SUNDAY NIGHT…MOSTLY CLOUDY WITH A CHANCE OF SNOW. LOWS IN THE

20S. SOUTHEAST WIND 15 TO 30 MPH EXCEPT EAST 25 TO 45 MPH THROUGH

PORTAGE VALLEY AND TURNAGAIN ARM.

TEMPERATURE / PRECIPITATION

SEWARD 23 23 31 / 100 100 60

GIRDWOOD 17 17 30 / 70 80 50

AVALANCHE DISCUSSION

Yesterday’s winds never really materialized. Today’s weather looks more significant and will effect the avalanche hazard. Today’s avalanche discussion is exactly like yesterday since yesterday ended up being a mellow weather day.

Today’s avalanche danger level will start at LOW and rise to MODERATE as winds materialize. 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.

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.

Jon and I hiked up Corn Biscuit yesterday, our pit showed easy failure on the newer snow interface as you would expect. Of interest was a moderate to hard sheer on the ground facets again. The snow pack was 3 ft deep. CTM/H 20 100cm, CTH29 100cm.

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 Sunday, December 20.