Good morning backcountry travelers this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Thursday December 3rd 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.
Will recent weather effect avalanche conditions today?
Well, let’s take a closer look at the precip, winds, and temps.
Hindcast (Last 24 hours)
3800′ -Sunburst Wx Station-
Temp: 21 (1 degree warmer than yesterday)
Wind: averaged calm to moderate 2-25 mph out of the East with a strong max gust of 41 mph
2600′-Seattle Ridge Wx Station-
This station broke down at 11pm Dec 1. Sorry about that, we will fix it as soon as possible.
1800′-Center Ridge Wx Station-
Precip: .1 inches of water and trace of new snow
minus 8” of total snowpack due to settlement
Temp: 24 degrees (same as yesterday)
Temps are cooling slightly in valley bottoms 2-3 degrees (compared to yesterday), and temps are slightly warmer on all ridgetops by 1-3 degrees. The temps range from 32 degrees at sea level to 21 degrees at 3800 feet.
Skies are cloudy in Girdwood as of 5am, and the Middleton Radar is back on line showing scattered light precip moving NE toward Cordova. Winds are currently calm at all ridgetop wx stations.
WESTERN PRINCE WILLIAM SOUND-
500 AM AKST THU DEC 3 2009
.TODAY…MOSTLY CLOUDY WITH SCATTERED SNOW SHOWERS IN THE
MORNING…THEN PARTLY CLOUDY IN THE AFTERNOON. HIGHS IN THE MID
20S TO UPPER 30S. VARIABLE WIND TO 10 MPH.
.TONIGHT…PARTLY CLOUDY. LOWS ZERO TO 25 ABOVE…COLDEST INLAND.
LIGHT WINDS EXCEPT NORTH 10 MPH NEAR SEWARD.
.FRIDAY…PARTLY CLOUDY. A SLIGHT CHANCE OF SNOW IN THE
AFTERNOON. HIGHS IN THE LOWER 20S TO LOWER 30S. VARIABLE WIND TO 10
MPH. NEAR SEWARD…NORTH WIND 10 MPH.
TEMPERATURE / PRECIPITATION
SEWARD 34 10 27 / 40 0 20
GIRDWOOD 36 11 25 / 40 0 0
Short Term Weather Models for higher elevations for Kenai Mountains near Turnagain Pass
Sea-level: 0 to .1 inches of water forecasted today
3000′: temps forecasted below freezing today with winds 10-15mph
6000′: temps forecasted below freezing today with winds 10-25mph
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 has decreased from CONSIDERABLE to MODERATE today. MODERATE is defined as: Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
My confidence in the snowpack is improving; however, there is still a deep instability that could have massive consequences. We saw a couple of medium sized natural avalanches (see photo gallery) on Tincan yesterday that probably avalanched during the height of the storm on Tuesday. The avalanche in the usual spot on the corniced ridge “CFR” on Tincan failed all the way to the ground on the facet layer, but it did not propogate very wide. We have seen almost the entire upper bowl avalanche before; so, its interesting that this more recent avalanche stayed isolated to a smaller area. There were also reports of natural avalanches on Sunburst and Magnum. We had bad visibility; so, we were unable to see these, but the Magnum avalanche was described as a large avalanche on the western aspect that faces the highway. The Sunburst avalanche was described as medium sized on the southern aspect near the top cone.
We went back to one of our study plots at 2000′ on Tincan to compare notes to CNFAIC Staff tests in that same area. We dug an unusually deep isolated column because we wanted to test those facets on the ground. This pit was 8 feet deep which is usually enough snow to reduce the effects of the stress bulb of a human on a weak layer; so, the test has some basic methodical flaws. This test, however, raised some eyebrows with this deep instability and is DEFINITLY worth talking about. Click the button on the upper left corner of this page to watch the video of yesterday’s test (12/2/2009. The column failed on the backcut on two differet tests. Both times, it failed right when Carl’s saw hit the facets near the ground. There is also a shallower weak layer in the storm snow, but the big picture here is that we still have a deep instability. I guess it could be possible for a human to trigger this deep instability if you found a shallower part of the surface snow where the wind tapered the slope, which, is common on places like the southern aspect of Sunburst or along the aspect facing the highway on the motorized side near “Repeat Offender” above the standard snowmachine up track. AnCNFAIC Staff possible way to trigger this weak layer could be by hucking off a ridge or cliff with your snowmachine. I don’t think it’s a good idea to impact the snow too hard right now. Travel one at a time, stay spaced out, watch your partners, and try not to jump off anything especially near ridgelines.
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.