Good morning backcountry travelers this is Carl Skustad with the Chugach National Forest Avalanche Information Center on Saturday December 5th 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).
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.
Hindcast (Last 24 hours)
3800′ -Sunburst Wx Station-
Temp: 25 (8 degrees warmer than yesterday)
Wind: averaged light to moderate 8-10 mph out of the ESE with gust of 24-40 mph
1800′-Center Ridge Wx Station-
Precip: 0 inches of water and 0 new snow
minus 3” of total snowpack due to settlement. Total snow depth is 67 ”
Temp: 25 degrees (3 degrees warmer than yesterday)
3400′-Frezno Ridge Wx Station-
Temp: 28 degrees (11 degrees warmer than yesterday)
Wind: averaging 8-11 mph with gust 19-24, northwest.
1200′-Summit Lake Wx Station-
Precip: 0 inches of water and 0 new snow
Total snow depth is 28 “, (down 1 due to settlement)
Temp: 19 degrees
Temperatures warmed back up a bit overnight. Temperatures range from 24 to 29 degrees with Summit Lake the out lier,19 deg. Winds are light to moderate out of the southeast.
The satellites show high cloud cover and the radars show no precipitation. Expect pretty mellow weather again today. Greybird. A 1055 mb high is sitting in central AK deflecting lows to our north. Expect this blocking high to be in place through most of the week.
WESTERN PRINCE WILLIAM SOUND-
500 AM AKST SAT DEC 5 2009
.TODAY…MOSTLY CLOUDY WITH SCATTERED SNOW SHOWERS. HIGHS IN THE
MID 20S TO LOWER 30S. NORTH TO EAST WINDS 5 TO 15 MPH. THROUGH
PORTAGE VALLEY AND TURNAGAIN ARM…WIND 15 TO 30 MPH.
.TONIGHT…MOSTLY CLOUDY WITH SCATTERED SNOW SHOWERS. LOWS IN THE
MID 20S TO LOWER 30S. NORTH TO EAST WIND 10 TO 20 MPH EXCEPT
SOUTHEAST 25 TO 35 MPH THROUGH PORTAGE VALLEY AND TURNAGAIN ARM.
.SUNDAY…MOSTLY CLOUDY WITH ISOLATED SNOW SHOWERS IN THE
MORNING…THEN PARTLY CLOUDY IN THE AFTERNOON. HIGHS IN THE 30S.
NORTH TO EAST WIND WIND TO 15 MPH EXCEPT SOUTHEAST WIND 15 TO 30 MPH
THROUGH PORTAGE VALLEY AND TURNAGAIN ARM.
.SUNDAY NIGHT…MOSTLY CLEAR. LOWS IN THE LOWER 20S TO LOWER 30S.
VARIABLE WIND TO 10 MPH.
.MONDAY…MOSTLY SUNNY. HIGHS IN THE UPPER 20S TO MID 30S. VARIABLE
WIND TO 10 MPH.
TEMPERATURE / PRECIPITATION
SEWARD 33 28 36 / 20 20 20
GIRDWOOD 31 25 32 / 0 20 0
Todays conditions are very similiar to yesterday. 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.
One more feature of concern includes ridge tops were wind is building wind slabs. These wind slabs are present and could take a person for a ride. These areas are considered complex terrain and careful routfinding needs to be executed.
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 6th. Thanks and have a great day.