Merry Christmas backcountry travelers! This is Kevin Wright with the Chugach National Forest Avalanche Information Center on Saturday, December 25th 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 and an increasing hazard trend if we get new snow predicted today. 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 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 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. We’ve been getting some reports from higher elevation terrain the last couple days. Expect 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 in that wind slab at 4200 feet 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. Traveling in these areas reaffirms my previous opinion: Right now you really have to look for instability to find it, but during the next major storm the stability will become dangerous. As we get more snow today be on the lookout for new windslab.
Yesterday I received a third hand report of a skier triggered slab in Goat Couloir above Girdwood. This is the type of terrain we’ve been worried about: high elevation, high consequence, steep, and wind loaded. The report said a 4-6 inch soft slab broke on the second turn down from the cornice at the top of the couloir. The skier was carried a short distance before skiing off the slab to the side and recovering. This apparently took all the soft snow out of the run, leaving the rain crust exposed, providing for very challenging skiing to get down the run. Any travelers in expert-only terrain like this should be prepared for little surprises. Fortunately no injuries were reported although I imagine there were some elevated heart rates! This area is at 6000 ft. and faces SSW.
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 standard 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. (Typical Turnagain is maritime, deep, dense, and stable snow. Hatcher pass is more intermountain climate with shallow, cold, light density snow with persistent instability.)
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:
Snow is finally predicted! It looks like just showers today, increasing to steady snow tonight. I don’t think this is the storm to cause widespread instability, but any new weight on the current snowpack adds to the stress and gets us closer to the tipping point. 2-8 inches of snow with 0.2 inches of water equivalent are predicted today. The CNFAIC Staff significant change today is warmer temperatures. It’s still well below freezing but any large temperature change stresses the snowpack and should be scrutinized. Wind was fairly minimal in the last 24 hours (max gust 22 on Fresno ridge). Expect the wind to pick up today.
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 SAT DEC 25 2010
.TODAY…CLOUDY WITH NUMEROUS SNOW SHOWERS. SNOW ACCUMULATION UP TO 2
INCHES. HIGHS ZERO TO 10 ABOVE EXCEPT IN THE LOWER 20S ALONG THE
COAST. NEAR SEWARD…NORTH WIND 20 TO 35 MPH. NEAR WHITTIER…WEST
WIND 15 MPH INCREASING TO 20 TO 35 MPH IN THE AFTERNOON.
.TONIGHT…CLOUDY. ISOLATED SNOW SHOWERS IN THE EVENING THEN
STEADY SNOW DEVELOPING OVERNIGHT. SNOW ACCUMULATION 1 TO 4 INCHES.
LOWS 5 BELOW TO 10 ABOVE EXCEPT AROUND 20 ALONG THE COAST. NEAR
SEWARD…NORTH WIND 20 TO 35 MPH. NEAR WHITTIER…WEST WIND
20 TO 35 MPH BECOMING VARIABLE 10 MPH AFTER MIDNIGHT.
.SUNDAY…SNOW. SNOW ACCUMULATION 3 TO 6 INCHES. HIGHS IN THE
TEENS TO MID 20S EXCEPT LOWER 30S ALONG THE COAST. NORTH TO
EAST WIND 10 TO 25 MPH.
.SUNDAY NIGHT…MOSTLY CLOUDY WITH A CHANCE OF SNOW SHOWERS.
LOWS 5 TO 20 ABOVE EXCEPT IN THE UPPER 20S ALONG THE COAST.
VARIABLE WIND TO 10 MPH.
.MONDAY…MOSTLY CLOUDY WITH A SLIGHT CHANCE OF SNOW SHOWERS.
HIGHS IN THE MID TEENS TO MID 20S EXCEPT LOWER 30S ALONG THE
COAST. LIGHT WINDS EXCEPT NORTH 10 TO 20 MPH NEAR SEWARD.
.MONDAY NIGHT…MOSTLY CLOUDY WITH A CHANCE OF SNOW SHOWERS.
LOWS IN THE TEENS.
.TUESDAY AND TUESDAY NIGHT…MOSTLY CLOUDY WITH A CHANCE OF SNOW.
HIGHS 15 TO 25. LOWS ZERO TO 15 ABOVE.
.WEDNESDAY THROUGH THURSDAY NIGHT…MOSTLY CLOUDY WITH A CHANCE
OF SNOW. HIGHS IN THE TEENS. LOWS ZERO TO 10 ABOVE.
.FRIDAY…SNOW LIKELY. HIGHS 5 TO 15 ABOVE.
TEMPERATURE / PRECIPITATION
SEWARD 20 18 31 / 40 80 80
GIRDWOOD 8 6 24 / 60 80 80
WEATHER STATION SUMMARY for Turnagain Pass:
-3800′ Sunburst Wx Station-
Temperatures rising. 17 degrees as of 0100. Light wind from the ENE.
-2600′ Seattle Ridge Wx Station-
Temperatures increasing. 13 degrees at 0100. Light and variable wind.
-1800′ Center Ridge Wx Station-
No new snow recorded (yet). Temperatures rising, currently 11 degrees.