Turnagain Pass

Good morning backcountry travelers this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Friday, November 26th 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). This advisory will expire 24 hours from the posting date/time.

ANNOUNCEMENTS

Turnagain Pass and Johnson Pass North Trail Head motorized use areas are open for snowmobile use. Adequate snow is present to prevent resource damage. These areas consist of the lands on the west side of the Seward Highway between the Turnagain Arm and Sixmile Creek and the drainage Southwest of Bench Creek adjacent to the Johnson Pass North Trailhead south to Bench Lake. Center and Divide Creek Drainages are closed to snowmachine use.

All CNFAIC Staff areas of the Chugach NF are closed to motorized use until December 1st or adequate snow to prevent resource damage.

WEATHER ROUNDUP

-TEMPS: Are 8-10 degrees colder at most weather stations compared to yesterday morning and below freezing at all weather stations. Sometimes glide cracks react to temperature swings. A 10 degree change is fairly significant. Give the glide cracks extra space today.

-PRECIP: Turnagain Pass snotel was not working this morning, but CNFAIC Staff snotels in the surrounding region recorded 0.3-0.4 inches of water with 4-8 inches of new snow. There is 0.0 inches of water forecasted today; so, no additional load in the form of precip.

-WIND: I suspect that most ridgetop weather station anemometers are iced up and not functioning properly this morning; so its, tough the say exactly what the wind is doing right now. Seattle Ridge at 2400′ appears to be working fine recording light winds averaging 0-9mph with a light max gust of 14mph in the past 24 hours. The National Weather Service is calling for moderate to extreme winds near Whittier today between 25-40mph. Watch out if these winds make it over to the mountains around Turnagain Pass.

Todays forecast for wind could increase the avalanche danger.

AVALANCHE DISCUSSION

The avalanche danger rating will remain at MODERATE due to the potential for small to medium sized human-triggered avalanches in the form of wind slabs along ridges and natural avalanches in the form of glide cracks that are widespread throughout the region.

The size of avalanches could increase today, if the wind increases and transports snow.

There is a 1/4 inch thick rain crust that extends up to the ridgetops to at least 3500′ (most likely well above 4000′). It is widespread throughout the Turnagain Arm area. This crust has all the characteristic to become a very dangerous weak layer as soon as there is more snow on top of it. The snow on top of this crust seems to be bonding fairly well at lower to mid elevations where the snow fell at warmer temps. Above 2500′, however, the snow on top of the crust IS NOT bonding well because of drier colder snow at these higher elevations. One of our observers found perfectly round ice pellets on top of the rain crust on Sunburst.

The 3 ingredients for dangerous avalanche conditions are: 1.)a slab, 2.)on top of a slippery bed surface, 3.)with a weak layer on top of the bed surface. We have 2 out of those 3. We are only missing a slab on top. Right now, the snow on steep slopes along the ridges just sluffs right off that rain crust.

Use extra caution along ridges where there are newly formed wind slabs or pockets of snow that look fat. These isolated pockets will not bond to the ice crust very well today. Pockets like these will be the most likely areas for human-triggered avalanches today.

The glide cracks and glide avalanches continue to be present, with new ones being observed region-wide on a daily basis. Be aware of your travel routes and try to avoid spending time below the cracks. The only way to reduce your risk from glide avalanches is to avoid traveling below the obvious cracks. We just had a fairly signifcant drop in temperatures. Sometimes glide cracks react to big temperature swings.

This photo shows a good example of a glide crack and a glide avalanche on the South face of Cornbiscuit taken on 11-16-10. For scale take note that the crack is 4-6 feet deep. The glide crack on the left hand side of this photo has already avalanched; while, the glide crack on the right is still a hazard that could avalanche any day. Avoid traveling underneath glide cracks just like the one on the right hand side of this photo.

The Nation Weather Service weather forecast for:

WESTERN PRINCE WILLIAM SOUND-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKST FRI NOV 26 2010

.TODAY…MOSTLY CLOUDY IN THE MORNING THEN BECOMING PARTLY SUNNY.

HIGHS IN THE UPPER 20S TO MID 30S. WEST WIND 25 TO 40 MPH NEAR

WHITTIER. NORTH WIND 15 TO 30 MPH NEAR SEWARD. NORTHWEST WIND TO 15

MPH ELSEWHERE.

.TONIGHT…MOSTLY CLOUDY. PATCHY FOG AFTER MIDNIGHT. LOWS 5 TO

15 ABOVE. NORTHWEST WIND 15 MPH.

.SATURDAY…MOSTLY CLOUDY WITH ISOLATED SNOW SHOWERS. HIGHS IN

THE UPPER 20S TO MID 30S…COOLEST INLAND. LIGHT WINDS.

TEMPERATURE / PRECIPITATION

SEWARD 36 16 33 / 0 0 20

GIRDWOOD 29 12 28 / 0 0 20

WEATHER STATION SUMMARY for Turnagain Pass:

3800′-Sunburst Wx Station

Temp (4am): 14 (10 degrees colder than yesterday morning)

Winds: *Anemometer is probably iced up and not working properly*In last 24 hours winds have been light averaging 0-3mph with a light max gust of 5 mph

2400′-Seattle Ridge Wx Station

Temp (5am): 17 (10 degrees colder than yesterday morning).

Winds: In last 24 hours have been light averaging 0-9mph with a light max gust of 14mph.

1800′-Center Ridge Wx Station

Temp (8pm Thurs 11/25): Weather station not reporting this morning. CNFAIC Staff similar snotel sites in the region recored 0.3-0.4 inches of water and 4-8 inches of new snow.

The next advisory will be issued tomorrow Saturday morning 11/27/2010 at 7am. If you get out in the backcountry send us your observations using the button at the top of this page or call and leave a message at 907-754-2369. Thanks and have a great day.