Good Morning backcountry travelers, this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Thursday, March 12, 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. This advisory expires in 24 hours and does not apply to operating ski resorts or highways/railroads.
MOUNTAIN WEATHER ROUND UP FOR THE LAST 24 HOURS
-General Weather Observations-
Most of the weather stations are down this morning. The SNOTEL sites are still working though, and they show a trace to 0.1 inches of precip in past 24 hours for Summit, Grandview, Turnagain Pass, and Girdwood. Temps are about the same as yesterday. It warmed up to 38 degrees at the Portage Lake Visitors Center yesterday. The NOAA models are forecasting .1 inch of precip for our area today.
–The NRCS Center Ridge weather station at 1800 feet in Turnagain Pass–
Has a temp of 25 degrees (1 degree colder than yesterday). 0.0-0.1 inches new water and a trace to 1 inch of new snow. Total snowpack depth is 68″.
–The Sunburst weather station at 3800 feet in Turnagain Pass–
….is down this morning
-Surface Analysis Maps-
Between 3am and 9pm yesterday….Not much going on. It looks like there are a couple of weak lows surrounding us.
The radars are not working this morning either, but the satellite shows moisture heading toward SE Alaska, but not toward us.
Primary avalanche concerns
-Below 3000 feet. The “Janurary Hurricane” rain crust buried under 1-4 feet of surface snow. There is a layer of weak sugary faceted snow on top and below this hard rain crust. We are finding DECREASING stability in spots on top of this crust. This weak layer is still showing signs of life, and probably will become very dangerous if it gets any sort of rapid load, especially rain.
-Sea-level up to at least 3800 feet (Probably higher). The thin “glazed donut” freezing rain crust that formed 3/5/09 has been observed in Girdwood, Turnagain Pass and Summit Lake. It was everywhere on all aspects and could become a bad weak layer if it gets buried under slaby snow.
AVALANCHES AND SNOWPACK
Normal Caution is advised above 3000 feet. Isolated pockets of Elevated Caution on slopes steeper than 35 degrees below 3000 feet is still advised today. We have a deep weak layer with that January Hurricane rain crust that is showing signs of decreasing stability. This weak layer has been reactive to human triggers in isolated areas, but it will probably require a big trigger like some serious weather especially rain to get it to avalanche.
That January Hurricane rain crust continues to adjust to the small amounts of weight that we continue to get slowly over time; although, the facets on top of this crust are growing. Don’t test your luck with this layer. Lisa has been digging pits every Monday for the past couple weeks at a study plot on Tincan. She has been finding decreasing stability with her shovel compression tests on top of the January Hurricane rain crust. The facets on top of that crust have become more sugary. Plus we got a report of frequent collapsing between 1200-1800 feet on Pete’s South at the southern end of Turnagain Pass. This party investigated these shooting cracks that propogated up to 70 feet long. They dug in the snow, and found that these cracks were failing on top of the Janurary Hurricane layer (see photo gallery). I was suprised on Tuesday to see how much the facets have developed at a study plot in Main Bowl along Seattle Ridge where I have been digging pits all season.
Eventually, the balance will get tipped and that layer will most likely create big avalanches. The question is where and when will this happen? The Seattle Creek Bowls and Placer/Skookum Valley slopes will be likely areas for that January Hurricane rain crust to avalanche if we every get hit with a big storm. Natural avalanches on this weak layer are unlikely today, but human-triggered avalanches are possible in the right spot. Watch out for super steep pockets below 3000 feet. Keep in mind that there is a a certain level of uncertainty with this weak layer. There is a chance the balance could get tipped with enough of these small increments of precip.
Once again, the NOAA weather forecast below does not sound like its going to pack a huge punch today, but that is exactly what we need to watch out for. Our snowpack has not had a major load for a while and it will probably not react very well whenever if it ever gets one.
WESTERN PRINCE WILLIAM SOUND-
500 AM AKDT THU MAR 12 2009
.TODAY…SNOW AND RAIN. SNOW ACCUMULATION UP TO 1 INCH. HIGHS IN THE
30S. NORTH TO WEST WINDS 10 TO 20 MPH.
.TONIGHT…SNOW LIKELY. SNOW ACCUMULATIONS UP TO 2 INCHES. LOWS IN
THE 20S. NORTH TO WEST WINDS 10 TO 20 MPH. LOCAL AREAS OF BLOWING
.FRIDAY…SNOW LIKELY IN THE MORNING…THEN A CHANCE OF SNOW IN
THE AFTERNOON. SNOW ACCUMULATION UP TO 1 INCH. HIGHS IN THE UPPER
20S TO MID 30S. NORTHWEST WIND 10 TO 15 MPH EXCEPT NORTH 25 MPH
TEMPERATURE / PRECIPITATION
SEWARD 37 26 33 / 80 60 60
GIRDWOOD 36 25 33 / 80 60 40
This concludes today’s avalanche advisory which will expire in 24 hours. The next advisory will be on Friday, March 13th (ooga booga). Thanks and have a great day.