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Issued
Fri, December 4th, 2009 - 7:00AM
Expires
Sat, December 5th, 2009 - 7:00AM
Forecaster
CNFAIC Staff
Avalanche risk The Bottom Line

Good morning backcountry travelers this is Carl Skustad with the Chugach National Forest Avalanche Information Center on Friday December 4th 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

All areas designated for snowmachines (except Placer and 20 Mile) on the Chugach National Forest are open. We are monitoring the snow at Placer and 20 Mile and will open those areas as soon as there is enough snow.

WEATHER ROUNDUP

Hindcast (Last 24 hours)

3800′ -Sunburst Wx Station-

Temp: 16 (5 degrees cooler than yesterday)

Wind: averaged calm to moderate 0-19 mph out of the SE with a gust of 0-28 mph

1800′-Center Ridge Wx Station-

Precip: 0 inches of water and 0 new snow

minus 5” of total snowpack due to settlement. Total snow depth is 70 ”

Temp: 22 degrees (5 degrees cooler than yesterday)

3400′-Frezno Ridge Wx Station-

Temp: 17 degrees

Wind: averaging 2-5 mph with gust to 10, south and northeast.

1200′-Summit Lake Wx Station-

Precip: 0 inches of water and 0 new snow

Total snow depth is 29 ”

Temp: 8.5 degrees (the cold hole)

Nowcast (OTW)

Temperatures continue to cool slightly. A slight inversion in the Summit Lake Area. Winds are light to moderate.

The satellites show high cloud cover and the radars show no precipitation. Expect pretty mellow weather today. Greybird. More of the same over the weekend as an Omega block of high pressure keeps the low pressure to the east. Continued clearing into the weekend.

Forecast

AKZ125-040100-

WESTERN PRINCE WILLIAM SOUND-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKST FRI DEC 4 2009

…STRONG WIND SATURDAY AFTERNOON THROUGH SUNDAY MORNING ALONG

PORTAGE VALLEY AND TURNAGAIN ARM…

.TODAY…MOSTLY CLOUDY. HIGHS IN THE LOWER 20S TO MID 30S.

VARIABLE WIND 10 MPH.

.TONIGHT…MOSTLY CLOUDY. LOWS IN THE MID TEENS TO LOWER 30S.

EAST WIND 10 TO 20 MPH.

.SATURDAY…MOSTLY CLOUDY. A SLIGHT CHANCE OF RAIN AND SNOW IN THE

AFTERNOON. HIGHS IN THE UPPER 20S TO UPPER 30S. EAST WIND 15 TO 30

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

MPH INCREASING TO 35 TO 50 MPH IN THE AFTERNOON.

.SATURDAY NIGHT…MOSTLY CLOUDY WITH A SLIGHT CHANCE OF RAIN AND

SNOW. LOWS IN THE LOWER 20S TO LOWER 30S. EAST WIND 25 TO 40 MPH

EXCEPT EAST 40 TO 55 MPH THROUGH PORTAGE VALLEY AND TURNAGAIN

ARM.

.SUNDAY…MOSTLY CLOUDY IN THE MORNING THEN BECOMING PARTLY

CLOUDY. HIGHS IN THE MID 20S TO MID 40S. EAST WIND 20 TO 35 MPH

DECREASING TO 10 TO 20 MPH IN THE AFTERNOON. THROUGH PORTAGE

VALLEY AND TURNAGAIN ARM…EAST WIND 40 TO 55 MPH DECREASING TO

20 TO 35 MPH IN THE AFTERNOON.

TEMPERATURE / PRECIPITATION

SEWARD 30 28 36 / 0 0 20

GIRDWOOD 20 16 29 / 0 0 0

AVALANCHE DISCUSSION

Today’s weather should not contribute to the avalanche danger. Natural avalanches will be unlikely, but small human triggered avalanches are still possible in specific areas like rocky areas near wind hammered ridges or anywhere the snowpack was tapered from the recent high wind event. Due to a current deep instability, there is still a chance for large avalanches in isolated areas. Due to time and lack of significant weather, the avalanche danger remains MODERATE today. MODERATE is defined as: Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

We have not seen or heard of any natural or human triggered avalanche activity since Tuesday’s storm. The usual suspect areas ripped out on Tin Can Ridge (south face), Sunburst (south face), and Magnum (west face) during that period. Since the snows subsided on Tuesday we have seen nice settlement and cooling temps. This process is making a more stable snowpack. The main area of concern lies at the ground where we still see faceted crystals from early November. This weak layer of snow is everywhere, from Anchorage to Seward. This is a typical setup for early winter in our area. Time should eliminate the reactivity of this deep weak instability. Both the lack of a temperature gradient and the pressure of the overlying snowpack will assist in this process. Areas we need to stay on our toes include thinner snowpacks. The sphere of influence (depth that a traveler’s weight will affect the snow) is about 3-4 feet deep for skiers and boarders, and 5-6 ft for snowmachiners. Snowpacks deeper than this have a stability advantage over shallower snowpacks. The sphere of influence will effect the weak faceted snow on the ground in shallower snows. Summit Lake, areas around Johnson Pass (Lips, Cornbiscuit, Silvertip) and all CNFAIC Staff areas with 3-5 foot snowpacks will have increased avalanche hazard.

As you plan your weekend keep this in mind. Shallower snow areas may bump the danger rating up to CONSIDERABLE. Take your time assessing shallower snowpacks. Send us your observations if you find good or poor stability. We have limited beta on Summit, Lost Lake, Johnson, and upper Glacier Valley.

There are also glide cracks opening up all over the place. These will continue to get wider and wider. People and dogs have fallen into these glide cracks in the past, and they can be very difficult to get out of.

This concludes today’s advisory. The next advisory will be December 5th. Thanks and have a great day.

Fri, December 4th, 2009
Alpine
Above 2,500'
0 - No Rating
Avalanche risk
Treeline
1,000'-2,500'
0 - No Rating
Avalanche risk
Below Treeline
Below 1,000'
0 - No Rating
Avalanche risk
0 - No Rating
1 - Low
2 - Moderate
3 - Considerable
4 - High
5 - Extreme
Avalanche risk Avalanche risk Avalanche risk Avalanche risk Avalanche risk
Travel Advice Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern. Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding, and conservative decision-making essential. Very dangerous avalanche conditions. Travel in avalanche terrain not recommended. Extraordinarily dangerous avalanche conditions. Avoid all avalanche terrain.
Likelihood of Avalanches Natural and human-triggered avalanches unlikely. Natural avalanches unlikely; human-triggered avalanches possible. Natural avalanches possible; human-triggered avalanches likely. Natural avalanches likely; human-triggered avalanches very likely. Natural and human-triggered avalanches certain.
Avalanche Size and Distribution Small avalanches in isolated areas or extreme terrain. Small avalanches in specific areas; or large avalanches in isolated areas. Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas. Large avalanches in many areas; or very large avalanches in specific areas. Very large avalanches in many areas.
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This is 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.