Good Morning backcountry travelers, this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Wednesday, December 31, 2008 at 7am. This will serve as a general backcountry avalanche advisory issued for the Turnagain Arm (Turnagain Pass is the core advisory area). Local variations always occur. Note: We issue advisories 5 days a week Wednesday-Sunday.
MOUNTAIN WEATHER ROUND UP
In the last 24 hours…
-The Center Ridge weather station at 1800 feet in Turnagain Pass-
Still no data. This weather station is down; so, let’s look at similar location at Grandview.
-The Grandview weather station at 1100 feet along the railroad tracks-
Recorded 0 inches of water or new snow. Current temp is -10 degrees F (4 degrees colder than yesterday)
-Sunburst weather station at 3800 feet in Turnagain Pass-
Recorded light winds averaging 1-6mph from the WNW with a light gust of 9 mph. Current temperature is 6 degrees F (3 degrees colder then yesterday)
-Surface Analysis Maps-
From 3 am Tuesday to 9pm last night…
Shows high pressure to our west getting slightly weaker. Doesn’t look like any storms are lined up fo us.
The analysis from 9pm last night showed the main flow going west-east toward Washington and Oregon. There is also a wierd north-south flow just to our west that looks like it would deflect any storm trying to head toward us. The jet stream is forecasted to stay below us over the next couple days.
As of 6:00 am this morning…Does not show much going on over us. Looks like clear skies to the west.
-General Weather Observations-
Compared to yesterday…Ridgetop temps are colder by 3-6 degrees F. Winds have been very light.
PRIMARY AVALANCHE CONCERNS
-October Facets on/near the ground
SECONDARY AVALANCHE CONCERNS
-Glide Cracks (see photos)
WATCH OUT SITUATIONS
-Big steep rollovers
-Shallow snow connected to deeper snow (photo gallery)
-If you hear any “whumpfing” or feel any collapsing, then get to safe terrain immediately and call it a day.
AVALANCHE AND SNOWPACK DISCUSSION
Went up Seattle Ridge to Main Bowl yesterday to investigate a shooting crack that was reported on Sunday as 2 feet deep and 60-80 feet long on an eastern aspect (Thanks for the observation Kevin). That was the biggest human-triggered activity reported or observed in the past couple days; so, we wanted to take a closer look.
The surface snow along Seattle Ridge was variable ranging from soft snow to stiff slabs due to last wind event. Before those winds came in, surface hoar and rimed snow were observed on the surface; so, my best guess is that this shooting crack was wind deposited snow on those old surface weak layers that are now buried in many places. There are still some slabs out there that are holding some energy, that could create small human-triggered avalanches on steep isolated terrain features.
Terrain management remains the key to safety with our existing snowpack. Thin early season snowpacks (like what we have right now) are not ready for the big lines that Alaska is famous for. We all need to keep our human factors in check and stick to planar slopes with clean runouts, and avoid steep or complex terrain. Use extra caution around rocks, gullies, or steep rollovers.
We have a grab bag of weak layers near the surface that will become a problem when the next big storm comes in….
-The recent clear weather, calm winds and cold temps have created a new batch surface hoar from the highway to the ridgetops in certain areas. Try to take note of where you see these feathery crystals especially on top of those old stiff wind slabs. Let us know where you see this; so, we can pass the word on to everybody else, and have a better idea of where the most dangerous areas will be after the next big storm.
-This cold weather has also created a bad temperature gradient in the top 1-2 feet (~40cm) of snow. Snow temperatures taken on Saturday on Sunburst (Thanks Bill) jive with snow temps taken in Main Bowl yesterday. Basically, this means that facets are forming in the current surface snow, which can become anCNFAIC Staff bad weak layer in the near future
-There is also a mystery layer of buried surface hoar that formed about 10 days ago that got buried under a couple inches of new snow on 12/24 and 12/25. This layer was most widesread at mid elevations up to 2800 feet, but was also observed on ridgetops up to 3800 feet.
Although the loose sugary facets that formed on the ground in October are showing signs of improved stability, this layer is still a concern for avalanches. Every snowpit this season shows that our snowpack consists of a dense slab on top of a weak layer of facets. Most of our stability tests show good stability on that layer of October facets right now. However, snow pits do not tell the whole story.
The weak layer of October facets failed during the last big storm (12/8/08) and resulted in large avalanches that propogated across very wide areas. This weak layer also failed with human-triggers 5 days after that storm near rocky and complex terrain near steep rollovers. These human-triggered avalanches where small relative to the entire slope and did not propogate very wide. They stayed isolated to specific terrain features, but these were very dangerous for people. I’m not sure, but these facets on the ground might still be an avalanche problem after the next big storm. What do you think?
WESTERN PRINCE WILLIAM SOUND-
500 AM AKST WED DEC 31 2008
.TODAY…PARTLY CLOUDY IN THE MORNING THEN BECOMING MOSTLY SUNNY.
HIGHS ZERO TO 15 BELOW EXCEPT 10 TO 15 ABOVE NEAR SEWARD AND
WHITTIER. NORTHWEST WIND 10 TO 15 MPH EXCEPT 25 TO 35 MPH NEAR SEWARD
AND WHITTIER. WIND CHILLS 15 BELOW TO 30 BELOW.
.TONIGHT…MOSTLY CLEAR. LOWS 10 BELOW TO 25 BELOW EXCEPT AROUND
5 ABOVE NEAR SEWARD AND WHITTIER. NORTHWEST WIND 10 TO 15 MPH.
WIND CHILLS 15 BELOW TO 30 BELOW.
.NEW YEARS DAY…PARTLY CLOUDY IN THE MORNING THEN BECOMING
MOSTLY CLOUDY. HIGHS 5 BELOW TO 10 ABOVE…COOLEST INLAND.
VARIABLE WIND TO 10 MPH. NEAR WHITTIER…WEST WIND 20 TO 30 MPH.
TEMPERATURE / PRECIPITATION
SEWARD 12 4 10 / 0 0 0
GIRDWOOD -2 -9 3 / 0 0 0