Good Morning backcountry travelers, this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Friday, December 26, 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-
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 .4 inches of water and 2″ of new snow (I’ll bet there was more like 7-8 inches of snow). Current temp is 16 degrees F (2 degrees warmer than yesterday)
-Sunburst weather station at 3800 feet in Turnagain Pass-
Recorded light winds averaging 3-17 mph from the northwest with a strong gusts up to 29 mph. Current temperature is 10 degrees F (1 degree colder then yesterday)
-Surface Analysis Maps-
From 3 am Thursday to 9pm last night…
Yesterday’s storm went over the top of us and now its sitting to our east in Prince William Sound. There is some high pressure to our west.
The analysis from 9pm last night showed the main flow going west-east over the top of us. It is forecasted move to our south.
As of 6:00 am this morning…Does not show much going on over us. Looks like clear skies to the west.
The Middleton radar shows that storm south of Prince William Sound. Most of the green monster is to the east of Cordova heading away from us in a southeast direction.
The Kenai radar shows scattered precitp; except, for a wall of light precip stacked up against the western edge of the Kenai Mountains.
-General Weather Observations-
Compared to yesterday…Temps are warmer at sea level by 5-6 degrees F. Mid elevations to the ridgetops are colder than yesterday by 1-4 degrees. Winds averaged light to moderate with strong gusts up to 39 mph. Winds are increasing on ridgetops this morning.
PRIMARY AVALANCHE CONCERNS
-New snow and wind slabs
-October Facets on the ground
-Crust (about 3.5 feet deep) with Buried Surface Hoar on Top (found at elevations below 2500 feet)
-Latest surface hoar near top of snow pack
SECONDARY AVALANCHE CONCERNS
-Glide Cracks (see photos)
WATCH OUT SITUATIONS
-Steep rollovers with wind slabs
-Rocky terrain of any kind
-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.
-Glide cracks bridged over.
AVALANCHE AND SNOWPACK DISCUSSION
There are most likely going to be some small-medium sized wind slabs out there today. Watch out for pockets of snow that look fat, especially on steep rollovers that drop out of view. This past storm probably did not put enough new weight on the October layer of facets to create any natural avalanches on that weak layer. Weather stations around our area only recorded .1 to .4 inches of water and 2-7 inches of new snow.
This new snow should be sitting on top of soft powder, but we did see surface hoar (and rimed snow) before this latest load came in. This was a difficult layer to track because it got buried under 1-2 inches of snow last week. There is definately a high level of uncertainty with this latest batch of buried surface hoar. We mostly saw it at mid elevations up to 2800 feet. Watch out in the bowls off Seattle Ridge. They are at the elevation where the biggest surface hoar crystals were observed.
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. Stay away from rocks, gullies, or steep rollovers.
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 entire snowpack is a consolidated 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 may be a problem after the next big storm.
WESTERN PRINCE WILLIAM SOUND-
500 AM AKST FRI DEC 26 2008
…BLIZZARD WARNING IN EFFECT UNTIL 4 PM AKST THIS AFTERNOON
.TODAY…MOSTLY CLOUDY WITH A CHANCE OF SNOW IN THE MORNING.
BLOWING SNOW IN WHITTIER WILL REDUCE VISIBILITIES TO ONE QUARTER
MILE OR LESS AT TIMES. HIGHS IN THE TEENS INLAND TO 20S ALONG THE
COAST. NORTH TO WEST WIND 15 TO 30 MPH. GUSTS TO 50 MPH IN SEWARD
AND 75 MPH IN WHITTIER.
.TONIGHT…PARTLY CLOUDY. LOWS 5 TO 20 ABOVE…COLDEST INLAND.
NORTH TO WEST WIND 10 TO 25 MPH. GUSTS TO 40 MPH NEAR SEWARD
.SATURDAY…PARTLY CLOUDY IN THE MORNING THEN BECOMING MOSTLY
CLOUDY. HIGHS 10 TO 20 ABOVE. NORTH TO WEST WIND 10 TO 15 MPH
WITH GUSTS TO 30 MPH NEAR SEWARD AND WHITTIER.
TEMPERATURE / PRECIPITATION
SEWARD 24 15 18 / 20 0 0
GIRDWOOD 20 7 14 / 40 0 0
TEMPERATURE / PRECIPITATION
SEWARD 27 24 24 / 100 100 40
GIRDWOOD 24 18 22 / 100 100 60