Good Morning backcountry travelers, this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Thursday, January 29, 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…
-General Weather Observations-
Temperatures have increased 6-9 degrees at all weather stations. Ridge top winds have been light to moderate averaging 8-17 mph with a few strong gusts up to 27 mph. A dusting to an inch or two of new snow fell yesterday.
–The DOT weather station near the crest the highway at Turnagain Pass at 1000 feet–
Is recording a temp of 25 degrees (8 degrees warmer than yesterday), calm winds averaging 4mph and the same total snowpack depth of 41 inches (same as yesterday).
–The NRCS Center Ridge weather station at 1800 feet in Turnagain Pass–
Has a temp of 26 degrees (9 degrees warmer than yesterday). It looks like 1 inch of new snow fell but zero water was recorded. Total snowpack depth is 61 inches.
–The Friends of the Avy Center Sunburst weather station at 3800 feet in Turnagain Pass–
Is recording a temperature is 20 degrees F (9 degrees warmer than yesterday). Winds have been light to moderate averaging 8-17 mph with a strong gust of 27 mph.
-Surface Analysis Maps-
From 3 am Wednesday to 9pm last night…
Show that same weak storm (992) from yesterday that was over the Aluetians moving NE towards us. It looks like we are on its outer arm.
The analysis from 9pm last night shows the main flow of the jet stream moving west to east over the top of us and to our south. In the next 48 hours, it is forecasted to shift to our south moving west to east pointing at BC and Washington.
Shows that the firehose is still pointed at SE AK.
The Middleton radar shows moderate amounts of green precip inside Prince William Sound. The Kenai radar shows some moderate green precip over Cook Inlet.
Primary avalanche concerns
-Deep slabs 2-6 feet thick on top of January facets
Secondary avalanche concerns
-Glide Cracks (now they are bridged over, don’t fall in)
WATCH OUT SITUATIONS
-New surface wind slabs on top of those slippery crusts
-Slopes that do not have a clean run out
AVALANCHE AND SNOWPACK DISCUSSION
Normal caution is advised. The January 14-16 storm, “The Hurricane”, left behind 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 leaving behind a thick rain crust. Above 2800 feet, the wind really hammered the snow up to the ridges leaving behind a smooth wind crust. Those deep slabs continue to be our main concern today, even though it is unlikely to trigger that weak layer. The next big avalanche concern will be new snow on top of those slippery crusts.
That weak layer of January facets has NOT been reactive to human triggers.
We are still finding those facets just about everywhere that we dig. Almost every stability test shows that it is very difficult to get that weak layer to fail, and when it does it is very low quality Q2-Q3. Stability tests show good stability on this weak layer.
Those facets WERE reactive to natural triggers during that last big storm.
We continue to find and get reports that more avalanches ripped out during that January 14-16 storm. Most of them avalanched below 3000 feet where the storm snow was heavy. Elevations above 3000 feet remained cold and dry; so, those January facets are still very sugary at higher elevations.
The avalanche hazard is low right now below 3000 feet, even though the text books say a slab on top of facets is a terrible combination for avalanches. There are still some question marks and pockets of elevated caution above 3000 feet. The weak layer of January facets might become a bigger concern during next large storm, especially if warm temps or rain make it above 3000 feet.
NOAA is not forecasting any drastic changes today (see forecast below).
I keep mentioning the glide cracks as a secondary concern mostly because they are now bridged over and are now more difficult to see. They could be a dangerous place to fall, like falling into a glacier crevasse. Be careful on the south side of Magnum where we have seen several glide cracks. Plus, I don’t really understand glide cracks. They seem to want to avalanche a different times for different reasons; so, I always treat them like cornices and 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 29 2009
.TODAY…SNOW SHOWERS. SNOW ACCUMULATIONS 2 TO 4 INCHES. HIGHS IN THE
UPPER 20S TO MID 30S. SOUTH TO EAST WINDS 10 TO 20 MPH.
.TONIGHT…SNOW. SNOW ACCUMULATION 1 TO 3 INCHES. AREAS OF BLOWING
SNOW AFTER MIDNIGHT NEAR SEWARD AND WHITTIER. LOWS IN THE UPPER TEENS
TO MID 20S. LIGHT WINDS. NEAR SEWARD…LIGHT WINDS BECOMING NORTH TO
WEST 10 TO 20 MPH.
.FRIDAY…SNOW LIKELY IN THE MORNING…THEN A CHANCE OF SNOW IN
THE AFTERNOON. SNOW ACCUMULATION UP TO 1 INCH. HIGHS IN THE UPPER
TEENS TO MID 20S. NORTH TO WEST WINDS 15 MPH. SEWARD AND
WHITTIER…NORTH TO WEST WINDS 20 TO 30 MPH. AREAS OF BLOWING SNOW
REDUCING VISIBILITIES TO ONE HALF MILE AT TIMES.
TEMPERATURE / PRECIPITATION
SEWARD 32 22 25 / 80 60 40
GIRDWOOD 30 18 22 / 100 80 60
Thanks for checking the CNFAIC avalanche advisory. Have a great day.