Good morning backcountry travelers this is Wendy Wagner with the Chugach National Forest Avalanche Information Center on Sunday, February 6th 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 remains at MODERATE with pockets of CONSIDERABLE for large deep slab avalanches. These are most likely to be triggered in shallow snowpack areas and rocky steep terrain. A MODERATE danger exists for recent wind slabs that have formed overnight on ridges.
The primary concern for today is deep slab avalanches. It has been close to 4 days since the most recent storm ended and, as of 6 am this morning, yesterday was the first day we have not heard any reports of natural or human triggered avalanches in our advisory area. Unfortunately, this does not mean the deep slab problem has skipped town. In fact, the nature of buried weak layers is to go through cycles of activation and dormancy. They tend to activate with either the weight of new snow or the weight of a person or snowmachine in just the right spot.
Locations most prone for triggering a deep slab are thinner snowpack areas such as those south of Turnagain Pass, beginning around the Johnson Pass, Lynx Creek area and through the Summit Lake and Carter Lake region. CNFAIC Staff thin locations are steep, rocky and complex terrain, especially where it may be hard to identify shallow spots. Remotely triggering an avalanche or triggering one above you or adjacent to you is possible. Route selection is the key. Are you connected to slopes over 35 degrees? Slides recently have been triggered from lower angle terrain, around 30 degrees, and have propagated and broke where the angle increased into the upper 30’s. Obvious clues to look for include any recent avalanches, whoomphing and shooting cracks. However, the catch is, these types of slides are notorious for breaking without warning.
Though areas such as Turnagain Pass and the Glacier Valley have deeper snowpacks, and saw less natural activity after the last storm, they are not out of the woods. The two avalanches in Seattle Creek two days ago on February 4th are ‘bulls eye clues’ that deep slab instabilities exist here as well. One avalanche was likely triggered remotely by a snowmachine, around 8′ deep, while the CNFAIC Staff was skier triggered and 4-5′ deep. Both these slides were generally westerly facing between 2300′ and 3000′.
Deep slab avalanches are scary because they can be hard to trigger and the consequences can be very high. This is the type of avalanche problem where the 2nd, 3th or 10th person on the slope triggers the bowl and takes out all previous tracks, including potentially themselves. Kevin posted a great ‘anatomy of a deep slab’ the past couple days which is now in the photo gallery, along with CNFAIC Staff great avalanche photos sent in to us.
As a secondary concern, the winds picked up from the northeast last night and are currently gusting into the mid 40’s on the ridges. With plenty of snow to transport expect to see fresh wind drifts on leeward slopes. These likely will be small but easy to trigger, especially along ridges. Keep in mind any recent wind deposited snow adds additional weight to a snowpack. This can tip the balance further for an avalanche to potentially break into deeper weak layers.
Outside of our advisory area: A report came in yesterday from Eagle River of a 1.5′ deep and 100′ wide remotely triggered avalanche by a skier as much as 100 meters away on low angle terrain. While this was not a deep slab (likely a persistent slab) it does illustrate the touchiness of the snowpack in general.
Encyclopedia of avalanche terms.
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!
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It has been just over three days since the storm laid down 50 inches at upper elevations in Girdwood and only 10-15 inches in the Summit Lake area. Turnagain pass ended up in the middle with around 29 inches. The past couple days have been mostly sunny and dry with colder air in the teens pooling in the drainage bottoms and nice temperatures in the 20’s at upper elevations. The winds increased from the east yesterday and were gusting into the 40’s on the peaks overnight. Today mostly cloudy skies with temperatures in the 20’s are forecast. Expect winds to continue and be in the 20 mph range with gusts in the 40’s on the ridge tops. A chance of snow showers starts today but little accumulation is expected, a trace to an inch possibly.
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.
This concludes my first advisory with the CNFAIC. Thank you everyone for your warm welcome and good luck Lisa on all your adventures!
The NWS weather forecast for:
WESTERN PRINCE WILLIAM SOUND-
500 AM AKST SUN FEB 6 2011
.TODAY…CLOUDY WITH SNOW SHOWERS MAINLY ALONG THE COAST.
UP TO 1 INCH SNOW ACCUMULATION. HIGHS IN THE LOWER TO MID 30S.
LIGHT WINDS EXCEPT EAST WIND 15 TO 25 MPH THROUGH PORTAGE VALLEY
AND TURNAGAIN ARM IN THE MORNING.
.TONIGHT…MOSTLY CLOUDY IN THE EVENING WITH A CHANCE OF SNOW
SHOWERS…THEN BECOMING PARTLY CLOUDY. LOWS IN THE TEENS TO
LOWER 20S INLAND AND 25 TO 30 ALONG THE COAST. LIGHT WINDS.
NEAR WHITTIER…WEST WIND 15 TO 25 MPH WITH GUSTS TO 35 MPH.
.MONDAY…MOSTLY CLOUDY WITH A CHANCE OF SNOW SHOWERS.
HIGHS IN THE UPPER 20S TO MID 30S. VARIABLE WIND TO 10 MPH.
.MONDAY NIGHT…SNOW. LOWS IN THE LOWER 20S TO LOWER 30S.
NORTH TO EAST WIND 10 TO 25 MPH.
.TUESDAY…SNOW AND RAIN. HIGHS IN THE 30S. NORTH TO EAST WIND
15 TO 30 MPH. THROUGH PORTAGE VALLEY AND TURNAGAIN ARM…EAST
WIND 25 TO 35 MPH INCREASING TO 35 TO 50 MPH IN THE AFTERNOON.
TEMPERATURE / PRECIPITATION
SEWARD 35 26 32 / 60 30 40
GIRDWOOD 35 18 32 / 20 20 20
WEATHER STATION SUMMARY for Turnagain Pass:
-3800′ Sunburst Wx Station-
Temperature 18 deg., rising trend. Winds steady NE in the 20’s, gusting 40’s, overnight and decreasing to the teens, gusting 20’s, at 5am.
-2600′ Seattle Ridge Wx Station-
Temperature 21 deg. Winds steady SE in the 20’s, gusting 40’s overnight.
-1800′ Center Ridge Wx Station-
Temperature 26 degrees. No new snow.