Good Morning backcountry travelers, this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Thursday, January 22, 2009 at 7am. This will serve as a general backcountry avalanche advisory issued 5 days a week Wednesday-Sunday for the Turnagain Arm area (Turnagain Pass is the core advisory area). Local variations always occur.
MOUNTAIN WEATHER ROUND UP
In the last 24 hours…
–The DOT weather station near the crest the highway at Turnagain Pass at 1000 feet–
Is recording a temp of 24 degrees (same as yesterday), calm winds and a total snowpack depth of 41 inches.
–The Center Ridge weather station at 1800 feet in Turnagain Pass–
Has a temp of 26 degrees (7 degrees warmer than yesterday). Total snow depth is 63 inches after 2 inches of settlement from yesterday.
–Sunburst weather station along the ridge at 3800 feet in Turnagain Pass–
Recorded calm winds averaging 1-14 mph from variable directions with gusts to 19 mph. Current temperature is 22 degrees F (5 degrees colder then yesterday)
-Surface Analysis Maps-
From 3 am Wednesday to 9pm last night…
Mostly shows a high pressure hovering to our south. These maps also show a bunch of low pressures near the Aluetians just hanging out and not doing much, but it looks like a pretty solid new storm just develeped out there. Maybe that one will head out direction.
The analysis from 3pm yesterday shows the main flow snaking around all over the place. Basically, its flows west to east then banks a big left turn toward us moving south to north then turns again and heads south toward SE Alaska. It is forecasted to mellow out above us and hang out to our south in a west to east flow over the next day or two.
Looks like a bunch of scattered clouds over us. Its also kind of interesting because you can clearly see the high pressure to our south spinning clouds clockwise, and the new low pressure storm near the Aleutians spinning counter clockwise.
Mostly clear, but there is a little precip creeping in from the south.
-General Weather Observations-
Temps got a little colder or stayed the same on the valley floors, and got a little warmer or stayed the same up to the ridges. For some reason, Sunburst is the oddball again today with a temp colder than yesterday. Winds have been calm.
Primary avalanche concerns
-Deep slabs 2-6 feet thick on top of Januray facets
Secondary avalanche concerns
-Glide Cracks (now they are bridged over, don’t fall in)
WATCH OUT SITUATIONS
-Higher elevations above 3,000 feet
-Slopes that do not have a clean run out
AVALANCHE AND SNOWPACK DISCUSSION
This past storm left behind deep slabs about 2-6 feet deep on top of a weak layer of facets that formed in early January. Rain and wet snow saturated the top 1-2 feet of the snowpack up to elevations of about 2800 feet. The wind really hammered the elevations above 2800 feet up to the ridges. Deep slab instability is our biggest concern.
My level of uncertainty has come down a little. We have a few more pieces of the puzzle, and new information has come to light. We confirmed the large avalanche that occured on Magnum failed at the bottom of the January facet layer. The stability tests on the crown profile looked very similar to most of the pits we have dug and matches reports from several CNFAIC observers from various locations. It is difficult to get those facets to fail, but they still do when you really hammer on them and they break out with lower quality shears between Q2 and Q3. I’m still confused why Magnum went big when nothing else did from that last storm.
We have found those facets on the both the motorized and non-motorized sides of Turnagain Pass, and they are still dry and well defined above 3000 feet. Below 3000 feet, these facets have been showing signs of rounding out possibly due to the heavy wet snow that fell on top of them. With that being said, its possible that these facets are still a dangerous weak layer above 3000 feet where ever they did not get destroyed by the strong winds from the last storm. There are still some question marks out there.
There are plenty of places to stay safe in the backcountry today, but we all need to work hard at keeping our human factors in check. Deep slab instabilities are bad. You probably will not trigger them, but if you do it will be a huge avalanche.
I keep mentioning the glide cracks as a secondary concern mostly because they are now bridged over and could be a dangerous place to fall. Plus I don’t really understand glide cracks. They seem to want to avalanche a different times for different reasons; so, I always try to avoid them. I don’t think we’ve seen the last of those things this year.
WESTERN PRINCE WILLIAM SOUND-
500 AM AKST THU JAN 22 2009
.TODAY…MOSTLY CLOUDY. A SLIGHT CHANCE OF SNOW SHOWERS IN THE
AFTERNOON. HIGHS IN THE LOWER 20S TO LOWER 30S. NORTH TO EAST
WIND TO 15 MPH EXCEPT EAST 15 TO 25 MPH THROUGH PORTAGE VALLEY
AND TURNAGAIN ARM.
.TONIGHT…CLOUDY WITH A CHANCE OF SNOW IN THE EVENING…THEN SNOW
LIKELY AFTER MIDNIGHT. SNOW ACCUMULATION UP TO 1 INCH. LOWS IN THE
20S. NORTH TO EAST WIND TO 15 MPH EXCEPT EAST 20 TO 35 MPH THROUGH
PORTAGE VALLEY AND TURNAGAIN ARM.
.FRIDAY…SNOW. SNOW ACCUMULATION 1 TO 3 INCHES. HIGHS IN THE
MID 20S TO MID 30S. NORTH TO EAST WIND 10 TO 20 MPH EXCEPT
EAST 25 TO 35 MPH THROUGH PORTAGE VALLEY AND TURNAGAIN ARM.
TEMPERATURE / PRECIPITATION
SEWARD 30 25 32 / 20 60 80
GIRDWOOD 28 26 30 / 0 40 80
Thanks for checking the CNFAIC avalanche advisory. Have a great day.