Good Morning backcountry travelers, this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Wednesday, January 28, 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 3-8 degrees or stayed the same as yesterday at most weather stations. Winds have been calm to light, but are showing signs of increasing this morning.
–The DOT weather station near the crest the highway at Turnagain Pass at 1000 feet–
Is recording a temp of 17 degrees (7 degrees warmer than 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 17 degrees (same as yesterday). Total snow depth is 62 inches. Zero new precip.
–Sunburst weather station along the ridge at 3800 feet in Turnagain Pass–
Recorded calm-light winds averaging 0-13 mph from variable directions with moderate gusts to 23 mph. Current temperature is 11 degrees F (1 degree warmer than yesterday)
-Surface Analysis Maps-
From 3 am Tuesday to 9pm last night…
Show a weak storm over the Aluetians getting slightly weaker as it slowly moves east (992-994).
The analysis from 9pm last night shows the main flow of the jet stream moving west to east just below us. It is forecasted to shift just slightly to our south moving west to east and point the firehose on SE Alaska.
Shows a bunch of warm moisture coming up from the south and hitting SE Alaska between Yakutat and Juneau. We are on the western edge of that flow, which looks like it is pulling moisture up toward us.
Shows a bunch of green precip outside of Prince William Sound moving NE. Some blue with a little green precip near Homer is making an appearance on the Kenai radar.
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 if weather forecast is accurate
-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. Those deep slabs remain are our main concern, even though it is unlikely to trigger that weak layer.
Last week, my level of uncertainty was high. Now, we have a lot more information. Basically, we have all been skiing and riding on a thick slab with a weak layer underneath it. Usually, that is not a smart thing to do. That weak layer of January facets, however, has NOT been reactive to human triggers.
Those facets WERE reactive to natural triggers during that last big storm. We continue to find and get reports of evidence that more avalanches ripped out during that storm. It appears that the entire upper cone of Eddies avalanched, and Superbowl or Goldpan had a good medium sized avalanche. Magnum still remains the largest avalanche where the majority of the west faced ripped out from the top down to tree line.
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 is good right now, even though the text books say a slab on top of facets is a terrible combination for avalanches. This weak layer might become a bigger concern during next large storm.
NOAA is forecasting 6-15 inches of snow for our area over the next 48 hours(see forecast below). This storm does not sound like it will pack a very large punch; so, I think the main concern if this storm hits us will be surface sluffs and wind slabs on top of that slippery supportable wind buffed layer on the steeper terrain at higher elevations that we have all been traveling on. It does not seem that snow is going to want to bond to that slippery layer, and I don’t think we will need to worry too much about avalanches stepping down to those January facets.
I keep mentioning the glide cracks as a secondary concern mostly because they are now bridged over and are difficult to see now. They could be a dangerous place to fall, like falling into a glacier crevasse. Be careful on the south side of Magnum. 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 WED JAN 28 2009
.TODAY…SNOW SPREADING NORTH THROUGH THIS MORNING. SNOW ACCUMULATION
2 TO 4 INCHES. HIGHS IN THE 20S. NORTH TO EAST WIND 15 MPH. PORTAGE
VALLEY AND EASTERN TURNAGAIN ARM…EAST WINDS TO 25 MPH. AREAS OF
BLOWING SNOW WITH VISIBILITIES TO ONE HALF MILE.
.TONIGHT…SNOW. SNOW ACCUMULATION 3 TO 6 INCHES. LOWS IN THE UPPER
TEENS TO MID 20S. NORTH TO EAST WINDS 15 MPH.
.THURSDAY…SNOW BECOMING MIXED WITH RAIN IN THE AFTERNOON. SNOW
ACCUMULATION 1 TO 5 INCHES. HIGHS IN THE UPPER 20S TO MID 30S.
VARIABLE WIND 10 MPH. NEAR SEWARD…LIGHT WINDS BECOMING SOUTH 15 MPH
IN THE AFTERNOON.
TEMPERATURE / PRECIPITATION
SEWARD 27 24 32 / 100 100 100
GIRDWOOD 25 21 30 / 100 100 100
Thanks for checking the CNFAIC avalanche advisory. Have a great day.