Good morning backcountry travelers this is Carl Skustad with the Chugach National Forest Avalanche Information Center on Saturday December 12th at 7 am. 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).
All areas designated for snowmachines (except Placer and 20 Mile) on the Chugach National Forest are open. Please remember that Center and Divide Creek near the Johnson Pass Trailhead are always closed due to the current Forest Plan. These areas are periodically patrolled by law enforcement. We are monitoring the snow at Placer and 20 Mile and will open those areas as soon as there is enough snow, these colder temps down low are really helping these areas.
3800′ -Sunburst Wx Station-
Temps finally dropped below freezing yesterday morning. The current temp is 29 deg F, 3 deg cooler than yesterday. Winds are light 7-10 with moderate gusts 9-13 mph out of the SE
2600′-Seattle Ridge Wx Station-
Winds are light 1-6 with moderate guest 8-10 out of the NE.
1800′-Center Ridge Wx Station-
Precip: 0 inches of water and 0 inches of new snow
minus 1” of total snowpack due to settlement for total depth of 55 inches
Temperature: 21 deg F same as yesterday.
Expect more foggy conditions today. The satalite and radar images indicate anCNFAIC Staff clear sky day above the fog layer. The dominate high pressure over southcentral continues to deflect any lows moving into the area. Expect this ridge of high pressure to break up Sunday evening. At that time expect colder temperatures and the chance of snow to increase. Once again expect temperatures close to the freezing mark at ridgetop elevations today and cooler temperatures at lower elevations. Our current temperatures range from 10 deg F at sea level to 29 on top of Sunburst. Summit Lake and Moose Pass are cooler with 5.7 deg F and -5 deg F respectively.
WESTERN PRINCE WILLIAM SOUND-
500 AM AKST SAT DEC 12 2009
.TODAY…MOSTLY SUNNY EXCEPT MOSTLY CLOUDY WITH AREAS OF FOG
IN THE TURNAGAIN ARM AREA. HIGHS 5 TO 15 ABOVE INLAND AND
IN THE 20S ALONG THE COAST. VARIABLE WIND TO 10 MPH. NEAR
SEWARD AND WHITTIER…NORTH TO WEST WIND 15 TO 25 MPH.
.TONIGHT…MOSTLY CLEAR EXCEPT MOSTLY CLOUDY WITH AREAS OF FOG
IN THE TURNAGAIN ARM AREA. LOWS 5 BELOW TO 10 ABOVE INLAND AND
15 TO 25 ABOVE ALONG THE COAST. LIGHT WINDS EXCEPT NORTH TO 15 MPH
.SUNDAY…INCREASING CLOUDS. AREAS OF FOG IN THE MORNING ALONG
TURNAGAIN ARM. HIGHS IN THE TEENS TO LOWER 20S EXCEPT MID 20S
TO LOWER 30S ALONG THE COAST. LIGHT WINDS EXCEPT NORTH TO 15 MPH
.SUNDAY NIGHT…MOSTLY CLOUDY WITH A CHANCE OF SNOW. LOWS IN THE
TEENS TO LOWER 20S EXCEPT IN THE 20S ALONG THE COAST. LIGHT WINDS
EXCEPT NORTH TO 15 MPH NEAR SEWARD.
.MONDAY…MOSTLY CLOUDY WITH A CHANCE OF SNOW. HIGHS IN THE
LOWER 20S TO LOWER 30S…COLDEST INLAND. LIGHT WINDS EXCEPT
NORTH TO 15 MPH NEAR SEWARD.
TEMPERATURE / PRECIPITATION
SEWARD 25 18 27 / 0 0 0
GIRDWOOD 16 12 18 / 0 0 0
Not much change in avalanche discussion today. Although this is our sixth day with a heavily inverted atmosphere, temps are dropping. Remember that an inversion means cooler air is trapped under warmer air aloft. This is an indication of a very stable atmosphere. Since our avalanche danger is low again today I’ll take the chance to mention a few things we need to remember from this weeks weather. Surface hoar formation from sea level to ~1500 feet. Wind and or melt freeze crusts above 2000 feet. A temperature gradient in the upper 6-8 inches of snow that is most likely forming near surface facets. Lastly, a bomber slab of snow setting on depth hoar (at ground). These will be important factors to remember when we get additional snow fall.
Due to insignificant results in recent snowpits, a lack of recent natural or human-triggered avalanches since Monday around Summit Lake, and a similar weather forecast from the NWS, today’s avalanche danger level will remain LOW. LOW is defined as: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. Natural and human-triggered avalanches unlikely. Very small avalanches in widespread areas; or small avalanches in isolated areas.
A special note for Summit Lake travelers. Additional observations indicate that the avalanche hazard may be slightly elevated in that area. A thinner snowpack may be responsible for this. My confidence level in this area is less than the Turnagain Arm Area. I will check with our Seward rangers today to get more clarification.
Normal Caution is advised.
With the very warm inverted air this week we are seeing a temperature gradient in the upper 6-8 inches of snow. Even though the air temperature reached the mid 40’s the low angle of the sun and the long wave radiation from the snowpack kept the surface snow temperatures below freezing. This is why we have not seen wide spread surface snow instability. This is however why we may see near surface faceting and miner sun crusts that will be our next week layer and bed surface.
The secondary concern today are glide cracks. Tincan in particular has lots of these crevasse like features. People and dogs have fallen into these before in the past, and they can be very difficult to crawl out of. Make sure your partner knows where you are around these glide cracks.
Always remember that safe backcountry travel requires training and experience. You control your own risk by choosing where, when, and how you travel. Follow your time tested backcounry rituals. One at a time, watch your partner and be prepared.
This concludes today’ advisory. The next advisory will be tomorrow morning at 7 am. Thanks and have a sun capped foggy day.