Good morning backcountry travelers this is Kevin Wright with the Chugach National Forest Avalanche Information Center on Friday, December 24th 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).
Placer and Skookum river drainages are OPEN to motorized use. Be aware of thin snow cover in certain areas. 20 mile drainage is still CLOSED until we get further snow cover.
Today the avalanche hazard is LOW, with pockets of MODERATE. Natural avalanches and human triggered avalanches are unlikely. Small human triggered avalanches are still possible in steep upper elevation windloaded terrain. Be on the lookout for pockets of stubborn wind slab in isolated areas at upper elevations. Persistent weak layers are widespread through the region, but most areas lack a sufficient slab to cause avalanches.
It has now been 3 weeks since a significant snowfall. Generally a prolonged high pressure trend like this leads to good stability, and that is currently true. Most commonly traveled terrain is seeing few signs of avalanche potential right now. Yesterday we got a chance to look at some higher elevation terrain, up to 4500 feet. We found highly variable conditions with scoured slopes on the windward side, exposing the rain crust at the surface. The lee side has stiff wind slab. A column test showed moderate failure on the facets just below the rain crust. CTM 19 Q2+ In a few places a 1-2 inch knife hard slab would break easily on top of the rain crust. One slope we skied was quite large, steep, and planar with just a few inches of light density snow on top of the rain crust. Traveling in these areas reaffirms my previous opinion: Right now you really have to look for instability to find it, but during the next storm the stability will be dangerous.
The slow internal weakening process in the snowpack could be leading to spontaneous instability even without a new load on top. This is part of the reason why we keep emphasizing the possibility of isolated avalanches on wind slabs in steep upper elevation terrain. This is not something I’d be worried about on average terrain, but could be an issue in exposed terrain with bad consequences below. The main message is: don’t let your guard down. It’s easy to get complacent when the stability has been so good for so long. Changes are still happening. Use all the safe travel protocol and good judgement in high consequence terrain. The current Turnagain/Kenai snowpack is different than normal (shallower) and more similar to a mid-season Hatcher pass snowpack. It should be treated differently as well.
For the long term outlook on avalanche conditions: Expect dangerous conditions when we get our next storm. A good rule of thumb is that the longer the stretch of clear weather, the more difficult it will be for the next snowfall to stick. In CNFAIC Staff words, after three weeks of clear and cold weather the current snowpack is weakening and the surface hoar will provide a poor bonding surface for new snow. Which means that when we do get a storm load on top of our current snowpack it will likely have poor stability and an elevated avalanche risk. The last significant snowfall was 10 inches on December 3rd. Since then the layers have been faceting and surface hoar has been forming.
Encyclopedia of terms:
Temperatures are cold from the valleys to the peaks, being slightly colder in the lower areas. Portage is reading –16 currently with ridgetops in the low single digits. Colder temperatures make for a larger temperature gradient, so expect the faceting process to be faster. The last snowfall was one inch on Monday. Wind has been light to moderate at the ridges. Expect mostly sunny skies today and cold temperatures. There is a slight chance of snow tomorrow and predicted warmer temperatures for the weekend.
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:
500 AM AKST FRI DEC 24 2010
…STRONG WIND THROUGH LATE THIS MORNING NEAR WHITTIER…
.TODAY…MOSTLY SUNNY. HIGHS 5 BELOW TO 10 ABOVE EXCEPT 15 TO 20
ALONG THE COAST. NEAR SEWARD…NORTH WIND 15 TO 30 MPH. NEAR
WHITTIER…SOUTHWEST WIND 15 TO 30 MPH WITH GUSTS TO 45 MPH
IN THE MORNING. ELSEWHERE…LIGHT WINDS.
.TONIGHT…PARTLY CLOUDY. LOWS ZERO TO 15 BELOW EXCEPT IN THE
TEENS ALONG THE COAST. NEAR SEWARD…NORTH WIND 10 TO 25 MPH.
NEAR WHITTIER…SOUTHWEST WIND 15 TO 30 MPH. ELSEWHERE…LIGHT
.CHRISTMAS DAY…MOSTLY CLOUDY. A SLIGHT CHANCE OF SNOW SHOWERS
IN THE AFTERNOON. HIGHS ZERO TO 10 ABOVE EXCEPT IN THE MID 20S
ALONG THE COAST. LIGHT WINDS EXCEPT NORTH AND WEST WIND 10 TO 20
MPH NEAR SEWARD AND WHITTIER.
.SATURDAY NIGHT…MOSTLY CLOUDY WITH A SLIGHT CHANCE OF SNOW
SHOWERS. LOWS 5 BELOW TO 10 ABOVE EXCEPT IN THE 20S ALONG THE
COAST. VARIABLE WIND TO 10 MPH EXCEPT NORTH WIND 15 TO 25 MPH
.SUNDAY…CLOUDY WITH A CHANCE OF SNOW. HIGHS IN THE TEENS TO
MID 20S INLAND AND LOWER 30S ALONG THE COAST. NORTH TO EAST
WIND TO 15 MPH EXCEPT NORTH 15 TO 25 MPH NEAR SEWARD.
.SUNDAY NIGHT…MOSTLY CLOUDY WITH A CHANCE OF SNOW. LOWS IN
.MONDAY THROUGH TUESDAY…MOSTLY CLOUDY WITH A CHANCE OF SNOW.
HIGHS 15 TO 25. LOWS 5 TO 15 ABOVE.
.TUESDAY NIGHT THROUGH THURSDAY…MOSTLY CLOUDY WITH A CHANCE
OF SNOW. LOWS ZERO TO 10 ABOVE. HIGHS IN THE TEENS.
TEMPERATURE / PRECIPITATION
SEWARD 18 13 24 / 0 0 20
GIRDWOOD 6 -2 10 / 0 0 20
WEATHER STATION SUMMARY for Turnagain Pass:
-3800′ Sunburst Wx Station-
Temperatures 4-8 degrees in the last 24 hours, currently 6 degrees. Wind has been light from the West.
-2600′ Seattle Ridge Wx Station-
Current temperature 1 degree. Wind light to moderate from the North.
-1800′ Center Ridge Wx Station-
No new snow. Temperature currently 0.