Good morning backcountry travelers this is Carl Skustad with the Chugach National Forest Avalanche Information Center on Saturday March 27th, 2010 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).
This week is Telepalooza week at Alyeska Resort. There are lots of great events and a fundraiser for the Friends of the Chugach National Forest Avalanche Information Center. Check Alyeska Resort’s webpage or www.telepalooza.com for a detailed schedule of events.
AnCNFAIC Staff nice day yesterday has lead us to cloud covered skies today. The leading edge of a 966mb L has already passed over our area. Temperatures and winds are currently climbing. The freeze line is forecasted to rise to 1300 ft from it’s current location at sealevel. Winds are also forecasted to increase significantly today. An active weather system with multiple low pressure systems is forcasted for the next week. Snow switching to rain today with 2-5 inches of snow at higher elevations.
Today’s avalanche danger is MODERATE with an increasing danger trend. Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully. Natural avalanches unlikely; human triggered avalanches possible.
We have multiple weak layers in the upper 3 feet of our snowpack. These layers consist of surface hoar on all aspects, and suncrusts on southerly aspects.
A couple more good snow stability tests came in yesterday indicating that our weak layers are not going away. The very dynamic nature of a spring snowpack require diligent snow analysis. Good snow stability in one couloir means nothing about the snow stability right around the corner.
Likely areas to trigger avalanches today include: steep hanging alpine snowfields near ridgetops and steep convex rollovers.
There are three main problem layers in the snowpack right now:
1. A sun crust with surface hoar on top is buried under Tuesday’s new 4-6 inches of new snow. We observed surface hoar on top of this crust in multiple locations. This layer could create small human-triggered avalanches on steep slopes where wind has deposited deeper snow.
2. A sun crust that is buried 2-3 feet deep (we have observed surface hoar near this crust) We have been finding moderate to hard failures with smooth shear planes on top and underneath this crust. It might become more reactive with a heavier load on top of it, or small avalanches might step down to this layer making medium sized avalanches.
3. Multiple layers of buried surface hoar in the top 1-3 feet of snow
There is a lot of spatial variability in the snowpack right now including multiple layers of buried surface hoar and buried suncrusts in the top 3 feet of snow. At lower elevations, there is a 1 inch thick breakable crust on all aspects up to about 1500-2000′ which is now buried under 4-6 inches of wet snow. Mid elevations to ridge top elevations generally have multiple buried suncrusts on southern aspects, but these crusts are very aspect-dependent and do not wrap around to CNFAIC Staff aspects. The uppermost suncrust was thin but it had surface hoar on top of it. Northern aspects at Turnagain Pass are generally thin, cold, and faceted especially in rocky areas.
Glide cracks are secondary concern today. These crevasse like features are those cracks that go all the way to the ground. One of these glide cracks avalanched a week ago on the southern aspect of Tincan to the lookers left of Tincan Proper (see photo gallery).
WEATHER FORECAST (National Weather Service)
WESTERN PRINCE WILLIAM SOUND-
500 AM AKDT SAT MAR 27 2010
…STRONG WIND THIS AFTERNOON THROUGH THIS EVENING THROUGH
PORTAGE VALLEY AND TURNAGAIN ARM…
.TODAY…RAIN AND SNOW IN THE MORNING…THEN RAIN SHOWERS IN THE
AFTERNOON. SNOW ACCUMULATION UP TO 2 INCHES…MAINLY AT HIGHER
ELEVATIONS. HIGHS AROUND 40. EAST WIND 10 TO 20 MPH INCREASING
TO 20 TO 35 MPH WITH GUSTS TO 50 MPH THROUGH PORTAGE VALLEY AND
.TONIGHT…RAIN SHOWERS. LOWS IN THE 30S. EAST WIND 20 TO 35 MPH
DIMINISHING TO 10 TO 25 MPH AFTER MIDNIGHT. GUSTS TO 50 MPH
THROUGH PORTAGE VALLEY AND TURNAGAIN ARM IN THE EVENING.
.SUNDAY…RAIN SHOWERS. HIGHS IN THE LOWER TO MID 40S. EAST
WIND 10 TO 20 MPH.
.SUNDAY NIGHT…RAIN SHOWERS LIKELY AND A CHANCE OF SNOW SHOWERS.
LOWS IN THE 30S. NORTH TO EAST WIND 10 TO 15 MPH.
.MONDAY…CLOUDY WITH A CHANCE OF RAIN AND SNOW SHOWERS.
HIGHS IN THE UPPER 30S TO MID 40S. NORTH TO EAST WIND 10 TO 15 MPH.
TEMPERATURE / PRECIPITATION
SEWARD 41 35 43 / 100 80 80
GIRDWOOD 39 36 41 / 100 80 80
WEATHER STATION SUMMARY for last 24 hours at TURNAGAIN PASS
3800′-Sunburst Wx Station
19 degrees F, 19 mph wind averages with gust to 32. Winds are increasing and easterly.
2600′-Seattle Ridge Wx Station
23 degrees F, 14 mph wind averages with gusts to 27. Winds are increasing and southeasterly.
1800′-Center Ridge Wx Station
26 degrees F, 0 new snow, 128 inches of total snowpack.
Thanks for checking today’s avalanche advisory. Lisa will update this advisory tomorrow morning by 0700. Thanks and have a great day.