Good morning backcountry travelers. This is Jon Gellings with the Chugach National Forest Avalanche Information Center on Tuesday, February 15th 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).
The avalanche danger today is MODERATE for deep slab avalanches in steep rocky terrain, as well as on slopes with a shallow snowpack. The possibility exists that any triggered avalanche could step down to deeper weak layers, creating a larger avalanche. If the winds keep transporting snow like they have been in many areas, we may see a CONSIDERABLE danger develop for pockets of sensitive wind slabs in wind loaded areas.
A report came in about a recent skier-triggered avalanche on Raggedtop in the Girdwood Valley. Information is currently limited, but this is what we have gotten:
-NE aspect on Raggedtop on 4-13
-Shallow, slid on a crust (possibly Thanksgiving Rain Crust)
-Broke on a convex rollover
-No burial, but did get caught and carried for 600-800 ft
-125 ft wide, 1000-1500 ft long
We will keep you informed if we find out any more information about the incident.
We also received a report two days ago of a skier triggered deep slab avalanche near Bench Lake in the Johnson Pass area on Friday, Feb 11. The weak layer that failed was unconsolidated facets near the ground. The slide was on a northwest facing slope around 36 degrees with the crown estimated at 30 inches.
These are the most recent reports of deep slab avalanches that we have heard about, but it is still our most concerning type of avalanche. These deep slabs can possibly be triggered in regions with a thinner snowpack, like the ones in Johnson Pass and in Girdwood, as well as in Summit Lake and some areas of Turnagain Pass. These shallow areas may allow a backcountry traveler to get into the middle of the slab before triggering it. You may also be able to trigger these from below steeper slopes, so avoiding avalanche run-out zones is advisable.
Recent strong winds have blown our light fluffy snow off of many windward slopes, and deposited much of it in pockets on leeward terrain. While the ridgetop weather stations in Turnagain Pass were unable to account for high winds in CNFAIC Staff areas, be well aware that many slopes may be holding new sensitive wind slabs which have buried a cold layer of low density snow. These areas could have increased danger, which warrants increased cautiousness throughout alpine terrain. Signs that you are travelling on a wind slab include seeing shooting cracks running away from you, and hearing hollow, drum-like sounds on hard snow. Convex rollovers and areas near a ridgeline are spots where triggering a windslab would be easiest. We may be talking more about this instability in the coming days.
The 7-12 inches of light fluffy snow on the surface has been showing signs of new snow instability. Loose snow sluffs and shallow soft slabs have been showing recent activity within the new snow density changes. These types of slides are much less dangerous than the deep instabilities and hard wind slabs mentioned above, but they are still no joke. Getting knocked down and buried is unlikely, but staying aware of this possibility could help keep a person out of trouble.
Encyclopedia of avalanche terms.
Winds are producing the biggest change in our snowpack currently. The highest recorded gust yesterday on our Friends weather stations was 30mph at Seattle Ridge. However, it was blowing significantly faster in many areas. Alpine temperatures have been increasing, and are now out of the negative range. Precipitation is unlikely today, as radar, satellite, models and forecasts all show clear weather.
The Friends of the CNFAIC (FCNFAIC) needs your thoughts! With a new staff of forecasters and a list of previously completed goals, the program is growing and potentially heading in new directions. The FCNFAIC wants to know what you have to say about YOUR avalanche center, so please complete the following anonymous survey by February 20th. Thank you in advance for taking it! Click here to take survey or cut and paste the address directly: https://www.surveymonkey.com/s/THWXVCD
I 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.
The NWS weather forecast for:
WESTERN PRINCE WILLIAM SOUND-
500 AM AKST TUE FEB 15 2011
…STRONG WIND THROUGH LATE MORNING NEAR WHITTIER…
.TODAY…SUNNY. HIGHS 10 TO 20 ABOVE. NORTH TO WEST WINDS 10 TO 20
MPH. NEAR WHITTIER…SOUTHWEST WINDS 40 TO 60 MPH DIMINISHING 20 TO
35 MPH BY AFTERNOON. NEAR SEWARD…NORTH WINDS 15 TO 30 MPH.
.TONIGHT…PARTLY CLOUDY. LOWS 5 BELOW TO 15 ABOVE…COOLEST
INLAND. NORTH TO WEST WINDS 10 TO 20 MPH. NEAR WHITTIER…SOUTHWEST
WINDS 15 TO 30 MPH.
.WEDNESDAY…MOSTLY CLOUDY. HIGHS IN THE 20S. NORTHWEST WIND
15 TO 30 MPH.
TEMPERATURE / PRECIPITATION
SEWARD 22 12 28 / 0 0 0
GIRDWOOD 17 4 25 / 0 0 20
WEATHER STATION SUMMARY for Turnagain Pass:
-3800′ Sunburst Wx Station-
Temperature 5 F. Westerly wind 10 mph gusting to the upper teens.
-2600′ Seattle Ridge Wx Station-
Temperature 5 F. North wind 3 mph gusting into the low teens.
-1800′ Center Ridge Wx Station-
Temperature 4 F. 0″ new snow. 86” total snow depth.