Good morning backcountry travelers this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Wednesday December 2nd 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 affect 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: 20 (6 degrees colder than yesterday)
Wind: averaged 10-62 mph out of the East with a max gust of 98 mph
2600′-Seattle Ridge Wx Station-
This station broke down at 11pm last night, but before that it recorded winds averaging 21-35 mph out of the SE with a max gust of 56 mph
1800′-Center Ridge Wx Station-
Precip: 2.0 inches of water
minus 5” of total snowpack due to heavy wet snow and temps up to 32 degrees
Temp: 25 degrees (5 degrees colder than yesterday)
Temps are colder at all weather stations from Girdwood to Summit Lake by 3-9 degrees. The temps range from 33 degrees at sea level to 20 degrees at 3800 feet.
Skies are clear in Girdwood as of 5am, and the radar is clear. Light to moderate winds are currently being recorded on ridgetops averaging as high as 24 mph on Sunburst
WESTERN PRINCE WILLIAM SOUND-
500 AM AKST WED DEC 2 2009
.TODAY…CLOUDY WITH SCATTERED RAIN AND SNOW SHOWERS. HIGHS IN THE
UPPER 20S TO UPPER 30S. SOUTH TO EAST WIND TO 15 MPH.
.TONIGHT…CLOUDY WITH NUMEROUS SNOW SHOWERS. LOWS IN THE MID 20S TO
LOWER 30S. SOUTHEAST WIND 10 TO 15 MPH.
.THURSDAY…DECREASING CLOUDS. SCATTERED SNOW SHOWERS IN THE
MORNING. HIGHS IN THE MID 20S TO LOWER 30S. VARIABLE WIND TO 10 MPH.
.THURSDAY NIGHT…MOSTLY CLEAR. LOWS 5 BELOW TO 20 ABOVE…
COLDEST INLAND. VARIABLE WIND TO 10 MPH.
TEMPERATURE / PRECIPITATION
SEWARD 37 30 31 / 40 40 60
GIRDWOOD 39 27 27 / 40 40 60
Some weather models are predicting .25” of more water today for the Kenai Mountains, with temps cooling off slightly, and moderate winds at 6000′.
Yesterday’s weather definitely contributed to today’s avalanche danger, but it looks like today’s weather should not pack a big enough punch to contribute any more additional stress today. The level of uncertainty with the snowpack is still very high today. Since the weather has backed off, the avalanche danger has also decreased from HIGH down to CONSIDERABLE today. Considerable means dangerous avalanche conditions exist, natural avalanches are possible, but human triggered avalanches are the area of main concern. Human triggered avalanches are still probable today on terrain steeper than 35 degrees especially around rocks, ridgelines, or anywhere the snow got tapered from the recent high wind and precip event. New storm snow from the last 48 hours will be the most likely snow to trigger an avalanche, but there is a deep slab instability lurking out there right now.
We drove up to Turnagain Pass yesterday, but did not go into the mountains for several reasons. The most important reason is that I have a strict rule of not putting myself in avalanche terrain during times of high avalanche danger and especially during intense storms. Snow science is not an exact science, but there is one fact from all the statistics on avalanche fatalities that can’t be ignored. That is…90% of avalanche accidents and fatalities occur DURING and WITHIN 24 HOURS of a storm. We are still in that time frame, don’t put yourself against the odds today. AnCNFAIC Staff fact that you can’t ignore is that most people die in avalanches when the avalanche hazard is rated CONSIDERABLE, just like it is today.
The reason why the level of uncertainty with the snowpack is high is because we have been slam dunked with weather for the past 9 days. We’ve been trying to get a baseline of the snowpack with pits at different elevations on Tincan over the past week. The weather has been changing so frequently that it is difficult for me to say anything about the snowpack with too much confidence.
The weird thing is that it has been difficult to feel or see any instability while skinning, making turns, or snowmachining. On the surface, the snow has felt good and strong, but we have been finding poor stability in ALL of our recent pits. These pits are a couple days old now, and they may not apply to the current conditions, but we have a scary deep slab instability out there. Take a couple minutes to click the You Tube button at the top of this page to see some of our recent isolated column tests. Deep slab instabilities can be difficult to trigger, but they go huge when they get triggered.
In simple terms, we have a dense slab on top of a weak layer of facets. All the new storm snow seems to be bonding to itself (creating a slab) very well. This dense snow seems to be supporting the weight of skiers/snowboarders and snowmachiners and this upper part of the snowpack is strong. When we have isolated columns, however, we have found poor stability with easy failures all the way to the facets on the ground.