Good morning backcountry travelers this is Carl Skustad with the Chugach National Forest Avalanche Information Center on Friday February 12th at 7 am. This will serve as a general backcountry avalanche advisory issued for Turnagain Arm Area with Turnagain Pass as the core advisory area (this advisory does not apply to highways, railroads, or operating ski areas).
Friday February 12th, 7:00 pm, at the APU Campus – Backcountry Film Festival!Benifits Alaska Avalanche School. more info at: www.alaskaavalanche.com
More of the same weather in store for us today. A ridge over Central AK extending to the lower 48 has lows grinding along it’s edge. These lows are spinning short wave precip into our area from the gulf. There are eight lows lined up to provide more damp, greybird weather through the weekend. Most of the precipitation will be rain at lower elevations and snow above 1500 ft. Amounts of precip are low. Only .5 inches a water forecasted today. The jet stream is to our south and not a large player in our local weather today. The satellites show three lows spinning counter clockwise in the gulf. The radar shows moderate precip coming across PWS. It is splitting into two fronts. One goes ashore near Seward and the second just north of Whittier, extending down the eastern shoreline of PWS to Cordova.
In the last 24 hours we received .4 to .7 inches of water. Above 1500 ft this came as snow. My best estimate this morning for new snow above the snowline is 4-10 inches. The higher the more snow. It is actively raining in the Girdwood Valley this morning and has been for the last 4 hours. Winds are strong with gusts in the 40’s to 60’s. Averages are 13 to 31 mph. All prevailing winds are out of the east.
Today’s avalanche hazard is MODERATE with pockets of CONSIDERABLE. This means that natural avalanches are unlikely, human triggered avalanches are possible. The pockets of considerable exist in areas near ridge tops where strong winds and or new snow is actively loading steep terrain. That means that natural avalanches may be possible in those pockets.
We don’t have a lot of intel on higher elevation stability yet. We need to continue to practice good route finding and snowpack evaluation skills in these areas. When we see storms trickling in over a longer period of time we see more spacial variability. This is the case today. Some areas see the wind, some don’t; some areas see snow or rain, some don’t. It is apparent that we are seeing an improvement in stability since the onset of this storm cycle last Friday. However, we have active weather adding wind, rain, and snow to the equation. This is the coastal weather building the coastal snowpack we all love. Stay heads up during this weather cycle.
There are two main weak layers in our snowpack. (Matt summed them up nicely so we’ll leave them posted today for review).
1.A thin breakable melt-freeze crust with surface hoar on top of it. We have seen this weak layer up to 3000′ on multiple aspects on both sides of highway at Turnagain Pass. This weak layer is generally buried 1 ½ to 2 ½ feet deep. Of course it will be buried deeper in areas where wind slabs formed. We were getting moderate failures with clean fast shears on this layer along Seattle Ridge on Monday 2/8/2010, but this weak layer was not reactive to human-triggers in certain locations on Monday (see forecasters video link for “backcountry artillery). Surface hoar has been observed on top of this layer in several pits. Not all pits show the surface hoar, and these feathery crystals get smaller as you gain elevation. This is the same weak layer that was responsible for the skier-triggered avalanches on Tincan on Saturday 2/6/2010. Plus I suspect this was the same weak layer that failed creating a natural avalanche on Widowmaker on Saturday 2/6/2010 as well (see photo gallery). This particular weak layer will be the likely culprit for human-triggered avalanches today.
2.The Jan 7 rain crust is generally buried 3-5 feet deep and it qualifies as a deep slab instability. As of yesterday 2/10/2010, it was still showing moderate failures with clean smooth shears. This weak layer is still showing significant signs of instability, but the question is what kind of trigger could create an avalanche on this weak layer? It appears that this weak layer will require a big trigger or more weight on top of it. This weak layer is widespread on all aspects between 2000-3000 feet.
WEATHER FORECAST (National Weather Service)
WESTERN PRINCE WILLIAM SOUND-
500 AM AKST FRI FEB 12 2010
…STRONG WIND THROUGH THIS AFTERNOON THROUGH PORTAGE VALLEY
AND TURNAGAIN ARM…
.TODAY…RAIN…EXCEPT RAIN AND SNOW THROUGH TURNAGAIN PASS.
SNOW ACCUMULATION UP TO 1 INCH. HIGHS IN THE UPPER 30S TO MID 40S.
NORTH TO EAST WIND 15 TO 30 MPH BECOMING SOUTH TO EAST 10 TO 20 MPH
IN THE AFTERNOON. THROUGH PORTAGE VALLEY AND TURNAGAIN ARM…EAST
WIND 35 TO 50 MPH DECREASING TO 25 TO 35 MPH LATE THIS AFTERNOON.
.TONIGHT…RAIN AND SNOW SHOWERS IN THE EVENING…THEN SCATTERED
SNOW AND RAIN SHOWERS AFTER MIDNIGHT. LITTLE OR NO SNOW ACCUMULATION.
LOWS IN THE UPPER 20S TO MID 30S. VARIABLE WIND 5 TO 15 MPH.
THROUGH PORTAGE VALLEY AND TURNAGAIN ARM…EAST WIND 20 TO 35 MPH
DECREASING TO 10 TO 20 MPH AFTER MIDNIGHT.
.SATURDAY…MOSTLY CLOUDY. ISOLATED RAIN AND SNOW SHOWERS
IN THE MORNING. HIGHS IN THE 30S. NORTH TO EAST WIND TO 15 MPH
EXCEPT NORTH WIND INCREASING TO 15 TO 25 MPH NEAR SEWARD.
.SATURDAY NIGHT…RAIN AND SNOW LIKELY. LOWS IN THE MID 20S TO
MID 30S. NORTH TO EAST WIND TO 15 MPH EXCEPT NORTH 15 TO 30 MPH
.SUNDAY…RAIN LIKELY. HIGHS IN THE MID 30S TO LOWER 40S. NORTH
TO EAST WIND 15 TO 30 MPH. THROUGH PORTAGE VALLEY AND TURNAGAIN
ARM…EAST WIND 15 TO 25 MPH INCREASING TO 25 TO 40 MPH IN THE
.SUNDAY NIGHT…RAIN AND SNOW LIKELY. LOWS IN THE 30S.
TEMPERATURE / PRECIPITATION
SEWARD 40 33 37 / 90 70 20
GIRDWOOD 39 29 38 / 90 70 0
Thanks for checking today’s avalanche advisory. The next one will be posted tomorrow Satuday February 13th.