Good Morning backcountry travelers, this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Wednesday, March 4, 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 does not apply to operating ski resorts or highways/railroads.
MOUNTAIN WEATHER ROUND UP FOR THE LAST 24 HOURS
-General Weather Observations-
Nothing too drastic is going on. Temps are warmer at most weather stations from Summit Lake to Turnagain Arm with the biggest change at sea-level with an increase of 11-15 degrees compared to yesterday morning. Winds have been light to moderate. The SNOTEL sites from Summit, Grandview, Turnagain Pass: recorded 0.0-0.2 inches of water and 1 inch of new snow.
–The DOT weather station near the crest the highway at Turnagain Pass at 1000 feet–
Is recording a temp of 34 degrees (5 degrees warmer than yesterday) with light winds and 1 inch of new snow.
–The NRCS Center Ridge weather station at 1800 feet in Turnagain Pass–
Has a temp of 11 degrees (3 degrees colder than yesterday). Zero inches water and zero inches of new snow has been recorded. Total snowpack depth is 69″.
–The Sunburst weather station at 3800 feet in Turnagain Pass–
Shows a temperature of 19 degrees (1 degrees warmer than yesterday). Winds have been calm to moderate averaging 1-11mph from variable directions with a max gust of 17mph.
-Surface Analysis Maps-
Between 3am and 9pm yesterday….Show a medium sized storm near the tip of the Aluetians getting weaker (972-979mb) as it heads in a NE direction toward Bristol Bay.
Not much going on near us on the Kenai or Middleton Radars. It looks like all the precip is on the west coast of AK near Bethel. That storm is pulling up a big arm of moisture from the south, but the NOAA forecasters are only calling for .25 inches of water for our location over the next 24 hours.
Primary avalanche concerns
-Below 3000 feet. 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 still finding moderate to hard instability on top of this crust in our stability tests. This crust is showing signs of being a very persistent weak layer.
-Above 3000 feet. Variable pockets of instability. Yeah, I know…Thats pretty generic, but we have had a report of a human-triggered class 2 slab up high.
AVALANCHES AND SNOWPACK
Normal Caution is advised in most areas, but there are some pockets of moderate avalanche hazard. The rain crust below 3000 feet is not likely to avalanche right now but it is still a serious concern and has the most potential for large avalanches. A big red flag for this lower elevation weak layer will be new rain on the existing snow.
We heard a fuzzy report of a human-triggered class 2 avalanche out in Skookum Valley on Monday above 4000 feet in elevation. Nobody was caught or injured in this avalanche but it shows that there are still a few suprises out there. We definatley do not have the best snowpack I’ve ever seen in my short time studying snow, but its not showing signs of widespread problems today. We are being haunted with the dreaded “isolated pockets of instability” right now. This is NOT one of those times when you can wildly attack the mountains without any worries. You really need to take the time to stick your head in the snow before you go. Its not a good time to do anything radical either. Strict travel rituals like skiing one at a time, watching your partners, and staying spaced out are always smart, but these strategies are essential right now.
That sugary snow (mixed forms facets) on top of that rain crust is still a problem. On Monday, Lisa found decreased stability on that layer compared to a pit from last week at a study plot on Tincan. Yesterday, we looked at that same weak layer on Eddy’s and found hard failures (CTH29Q2@68cm) but this test shows that this weak layer is still showing signs of life. It will become a problem with any big weather event, especially rain on snow.
Up high, we continue to see multiple density changes in the surface snow and there have been pockets of buried surface hoar reported. The most likely place to find these landmines will be in areas that are consistantly protected from wind. Our pit yesterday had a very clean and quick failure about a foot deep (CTM16Q2@28cm). I thought that screamed of buried surface hoar, but I did not see any signs of it through my magnifying glass. It doesn’t really matter. We know that there are multiple layers in the top 3 feet of snow, and some of those layers are failing on clean quality shears. These types of weak layers can heal up fairly fast, but they probably will not like a rapid heavy load of snow from wind or new precip.
500 AM AKST WED MAR 4 2009
.TODAY…CLOUDY WITH A CHANCE OF SNOW. HIGHS AROUND 30. VARIABLE WIND
TO 10 MPH. NEAR WHITTIER…WEST WIND 25 TO 35 MPH DECREASING TO 15
MPH IN THE AFTERNOON. NEAR SEWARD…NORTH WIND 20 TO 30 MPH
DECREASING TO 15 MPH IN THE AFTERNOON.
.TONIGHT…SNOW AND AREAS OF BLOWING SNOW. SNOW ACCUMULATION 1 TO 2
INCHES. LOWS IN THE MID 20S TO LOWER 30S. SOUTHEAST WIND 10 TO 15 MPH
EXCEPT EAST 20 TO 35 MPH THROUGH PORTAGE VALLEY AND TURNAGAIN ARM.
.THURSDAY…RAIN AND SNOW. SNOW ACCUMULATION 1 TO 2 INCHES. HIGHS IN
THE 30S. SOUTHEAST WIND 10 TO 15 MPH. THROUGH PORTAGE VALLEY AND
TURNAGAIN ARM…EAST WIND 25 TO 40 MPH DECREASING TO 15 TO 25 MPH IN
.THURSDAY NIGHT…SNOW LIKELY. LOWS 15 TO 25. WEST WIND 10 TO 20 MPH.
TEMPERATURE / PRECIPITATION
SEWARD 31 28 36 / 60 60 80
GIRDWOOD 29 27 33 / 60 60 80
This concludes today’s avalanche advisory the next advisory will be on Thursday, March 5th. Thanks and have a great day.