Good morning backcountry travelers this is Kevin Wright with the Chugach National Forest Avalanche Information Center on Friday, December 31st 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 hazard rating is CONSIDERABLE today. We have a little bit of new snow and high wind overnight. Wind slabs at upper elevations are the primary concern. Natural avalanches will be possible and human triggered avalanches likely in certain terrain. Expect smaller avalanches in many areas.
We’re in the middle of a tough prediction cycle right now. The snowfall has generally fallen short of predictions, bringing 10-12 inches to Turnagain Pass the last few days. High wind has redistributed that snow up high, so wind slabs are a concern today.
Yesterday I predicted dangerous avalanche conditions and that never really happened. The storm broke early and left only 3 inches new snow by late morning. If you did make it into the backcountry you were treated to relatively safe conditions and good visibility. Since then the wind has continued and we have gotten a little more snow.
Primary concern: Wind slab. Wind blowing into the 50s, predominately from some variation of east at the ridges, means the western slopes will be loaded. Intense wind like this can sometimes drop the snow a little bit lower onto the slope, so be cognizant of depth early as you approach the ridges.
Secondary concern: Persistent weak layers. This new snow is sitting on top of many different suspect layers ranging from the Thanksgiving rain crust, facets, and buried surface hoar.
Added weight equals added stress. Any new stress on top of known persistent weak layers needs to be treated with respect, especially during the storm. If anyone notices avalanches breaking into these old weak layers please send us your observations.
During a storm cycle is a great time to use good terrain management to stay safe in the backcountry. Pay close attention to the wind distribution patterns and relative snow depth as you travel. Caution should be high at upper elevations, near ridges, and in any steep, high consequence terrain.
The problem with this setup is that it makes snow assessment difficult. We could be looking at moderate to considerable danger ratings for a while as the hazard never
really spikes and never really drops. We’re dealing with lots of unreliable weak
layers that are just waiting for that right amount of stress before they fail and
cause an avalanche. As our new snow has time to set up the slab we’re worried about gains strength and cohesiveness. Strength in the slab means that triggering becomes more difficult but potential avalanche size becomes larger.
Encyclopedia of avalanche terms.
Yesterday’s predicted storm fizzled out pretty early. Turnagain pass received only 3 inches of slightly heavier snow, added to Wednesday’s 7 inches of light powder. During the day we got good visibility and saw very little evidence of avalanche activity. Overnight the wind picked up, gusting into the 50s in some areas. The temperature has also risen significantly. The freezing line is around 1500 feet, which means rain at lower elevations. Right now the storm continues but looks like it isn’t producing much in the Turnagain/Girdwood region. Flow is from the south, putting us in the rain shadow and giving Seward a direct hit. Today the same weather is predicted, with precipitation as rain or snow depending on elevation. High wind is expected to diminish this afternoon.
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 FRI DEC 31 2010
…STRONG WIND THIS MORNING THROUGH PORTAGE VALLEY AND TURNAGAIN
…STRONG WIND SATURDAY THROUGH SUNDAY AFTERNOON THROUGH PORTAGE
VALLEY AND TURNAGAIN ARM…
.TODAY…RAIN…MIXED AT TIMES WITH SNOW OVER HIGHER ELEVATIONS AND
INLAND AREAS. ISOLATED AREAS OF LIGHT FREEZING RAIN INLAND. MOSTLY
CLOUDY THIS AFTERNOON WITH SCATTERED RAIN AND SNOW SHOWERS. LITTLE
SNOW ACCUMULATION. HIGHS IN THE LOWER TO MID 30S. THROUGH PORTAGE
VALLEY AND TURNAGAIN ARM…EAST WIND 35 TO 55 MPH DIMINISHING 10 TO
20 MPH BY AFTERNOON. ELSEWHERE…SOUTH TO EAST WINDS 15 TO 30 MPH
DIMINISHING TO 15 MPH THIS AFTERNOON.
.TONIGHT…SNOW LIKELY AFTER MIDNIGHT. SNOW ACCUMULATION UP TO 2
INCHES. LOWS IN THE LOWER 20S TO LOWER 30S. VARIABLE WIND 10 MPH
INCREASING TO EAST 15 TO 30 MPH AFTER MIDNIGHT.
.NEW YEARS DAY…SNOW IN THE MORNING…THEN RAIN AND SNOW IN THE
AFTERNOON. PRECIPITATION MAY BE HEAVY AT TIMES IN THE AFTERNOON.
SNOW ACCUMULATION 2 TO 6 INCHES…HIGHEST AMOUNTS INLAND AND AT
HIGHER ELEVATIONS. HIGHS IN THE 30S. THROUGH PORTAGE VALLEY AND
TURNAGAIN ARM…EAST WIND 35 TO 45 MPH INCREASING TO 50 TO 60 MPH IN
THE AFTERNOON. SOUTHEAST WINDS 20 TO 40 MPH ELSEWHERE.
.SATURDAY NIGHT…RAIN AND SNOW LIKELY. LOWS IN THE UPPER 20S TO
MID 30S. THROUGH PORTAGE VALLEY AND TURNAGAIN ARM…EAST WIND 50 TO
60 MPH. ELSEWHERE…SOUTH TO EAST WINDS 20 TO 40 MPH.
.SUNDAY…RAIN AND SNOW LIKELY. HIGHS IN THE LOWER TO MID 30S.
SOUTHEAST WIND 15 TO 30 MPH EXCEPT EAST 35 TO 50 MPH THROUGH
PORTAGE VALLEY AND TURNAGAIN ARM.
.SUNDAY NIGHT…CLOUDY WITH A CHANCE OF SNOW. LOWS IN THE 20S.
.MONDAY THROUGH TUESDAY…MOSTLY CLOUDY WITH A CHANCE OF SNOW.
HIGHS IN THE 30S. LOWS IN THE 20S.
.TUESDAY NIGHT THROUGH THURSDAY…MOSTLY CLOUDY WITH A CHANCE OF
SNOW. LOWS 15 TO 25. HIGHS 25 TO 35.
TEMPERATURE / PRECIPITATION
SEWARD 35 27 36 / 90 80 80
GIRDWOOD 32 24 34 / 90 60 60
WEATHER STATION SUMMARY for Turnagain Pass:
-3800′ Sunburst Wx Station-
Temperatures into the mid 20s. Wind gusting to 58, consistently from the ENE and strongest the last few hours.
-2600′ Seattle Ridge Wx Station-
Temperatures to 27 degrees. Max gust 52 from the ESE
-1800′ Center Ridge Wx Station-
About 0.3 inches of snow water equivalent fell since yesterday. Temperatures at or near freezing, so expect an inch or two of wet heavy snow.