Good morning backcountry travelers. This is Jon Gellings with the Chugach National Forest Avalanche Information Center on Wednesday, February 23rd at 7am. This will serve as a general backcountry avalanche advisory issued for Turnagain Arm with Turnagain Pass as the core advisory area (this advisory does not apply to highways, railroads, or operating ski areas).
We have a new survey for you to fill out, which would hopefully involve all backcountry skiers in North America. The focus is on the differences between all male, all female, and mixed gender ski groups, and is actually being conducted by a local APU student. Please fill it out, which should take about 10 minutes.
Click here to take survey
Today, the avalanche danger is MODERATE, with pockets of CONSIDERABLE. The strong winds from the past few days look as though they have finally settled down, and they have definitely affected our snowpack. The decreasing danger is aimed directly at this hazard, since loading processes have seemingly ceased in most areas, but human triggered avalanches are still likely. Slopes that have not received a wind load still contain a steady MODERATE danger for deep slabs, which are still possible to trigger on slopes steeper than 30 degrees in areas with a relatively shallow snowpack (less than 2 meters deep).
The snowpack surface in Turnagain Pass is very heavily wind affected in most places not protected by trees. Hard wind slabs, soft wind slabs, sastrugi, and wind crusts are the replacements for the “cold smoke powder” many people have been reporting over the past weeks. These surface features also make observing recent avalanches fairly difficult in some areas. We were able to see many things that looked like new avalanches in wind loaded areas yesterday, but the winds nearly obliterated their tracks, leaving a little feeling of doubt on how new they really were.
These avalanches in the same gulley on Seattle Ridge do not easily show their tracks, but the upper one was very crisp, meaning that it was quite recent and perhaps failed overnight. There is a pocket of deeper instabilities about halfway down the slope that pulled out down to the ground, which is the first slab breaking into these older weak layers in Turnagain Pass in several weeks. This goes to reiterate the fact that this instability can be triggered in Turnagain Pass, not just in CNFAIC Staff areas.
One person wrote in an observation for Hatcher Pass giving details of a slab avalanche that happened on Monday. Although this is outside of our advisory area, I feel it is worth mentioning. Two people were climbing a North-facing chute on Marmot when it broke 2-2.5ft deep, carrying them ~100 yards and partially burying one of them. There are no details of injuries, but it goes to show that instabilities are potentially everywhere this year. Collapses and shooting cracks were also observed in the Summit Lake area as recently as yesterday, so there is anCNFAIC Staff heads up.
Signs that you are travelling on a wind slab include seeing shooting cracks, and hearing hollow sounds on hard snow. A soft slab could be easily triggered near convex rollovers and/or ridgelines, while hard slabs are a bit more unpredictable. They tend to fracture when a person gets out in the middle of them, and break like glass sending travelers to the bottom of the slope. And the possibility still exists for a moving avalanche to break into deeper weak layers, creating a larger avalanche.
We are still concerned with the possibility of deep slab avalanches, and the slab near Twin Peaks is the largest one recently observed. It propagated fairly wide, and slid down to the ground in most areas. These deep slabs can possibly be triggered in regions with a snowpack generally less than two meters deep, and conditions are not likely to improve until we get a large storm with lots of water which causes these layers to fail and eventually strengthen. Until then, know the snow you are on to avoid this hazard.
Here are two side notes of information:
1. We have not seen a perceived LOW danger since between Christmas and New Years. We would all love to see stable conditions, but we simply cannot rule out the possibilities and/or likelihoods of triggering a life-altering slab avalanche.
2. The Western Chugach National Forest (our area) has several NRCS sites which measure snow-water equivalent, and all are recording 66-88% of normal for this time of year. This low-snow year is more comparable to an intermountain or continental snowpack, versus our normal maritime snowpack.
Encyclopedia of avalanche terms.
Wind sensors on weather stations are showing decreased winds, so hopefully they are done blowing for the time being. Temperatures should be similar to yesterday, with solar warming potentially starting up on Southern aspects. New precipitation is unlikely today, as radar, satellite, models and forecasts all show clear to partly cloudy weather.
Kevin will issue the next advisory tomorrow morning at 7am. If you get out in the backcountry give us a call at 754-2369 or send us your observations using the button at the top of this page. Thanks and have a great day.
NWS Turnagain Pass Weather Forecast
WEATHER STATION SUMMARY for Turnagain Pass:
-3800′ Sunburst Wx Station-
Temperature 15 F. West winds 5 mph gusting to 9 mph.
-2600′ Seattle Ridge Wx Station-
Temperature 15 F. Southwest wind 1 mph gusting to 6 mph.
-1800′ Center Ridge Wx Station-
Temperature 9 F. 0″ new snow. 86” total snow depth.