Good morning backcountry travelers this is Lisa Portune with the Chugach National Forest Avalanche Information Center on Sunday, November 28th at 6am. 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).
Turnagain Pass and Johnson Pass North Trailhead motorized areas are open for snowmachine use. Adequate snow is present to prevent resource damage. These areas consist of the lands on the west side of the Seward Highway between the Turnagain Arm and Sixmile Creek and the drainage southwest of Bench Creek adjacent to the Johnson Pass North Trailhead south to Bench Lake. Center and Divide Creek drainages are closed to snowmachine use. All CNFAIC Staff areas of the Chugach NF are closed to motorized use until December 1st or until adequate snow falls to prevent resource damage.
Last night a weak low pressure system dropped 3 inches of new snow in Turnagain Pass. Ridgetop winds were light yesterday while mountain temperatures warmed up to the low 20’s. AnCNFAIC Staff inch or two of snow may accumulate in the mountains this morning, but skies should clear by afternoon. Winds are currently light and variable while mountain temps this morning are in the high teens. Cold arctic air will dive down into southcentral today as a strong ridge of high pressure moves over the mainland for the upcoming week. Mountain temperatures will continue to drop throughout the day and hit the single digits by this evening while ridgetop winds will increase this afternoon and average15-30mph out of the northwest.
Today the avalanche hazard will increase to MODERATE on steep windloaded slopes greater than 35 degrees while slopes not affected by the wind will have a LOW danger. New windslabs on top of a slick ice crust will be our main concern later today as the winds increase. By late this afternoon, small to medium sized natural and human-triggered avalanches will be possible on steep windloaded slopes if the north winds start cranking. Watch for crossloading down off the ridgelines where the snow is softer and more transportable. Lingering pockets of 2-day old windslab may also exist at the higher elevations this morning, so use extra caution before committing to steep lines. Glide cracks continue to avalanche unpredictably and remain a secondary concern today.
Our snow surface this morning consists of 7-10 inches of fluff on top of a super slick ice crust that formed during the freezing rain event last Monday. Matt and I toured up to the Sunburst weather station yesterday and confirmed that the ¼ inch thick ice crust extends to 4000 feet elevation and most likely higher. Right now the surface snow lacks cohesion and simply sluffs on steep slopes. Even moderate winds will drive this snow into dense slabs that will slide easily on the ice crust. I have a feeling we will be dealing with this stout ice layer for a long while, now officially dubbed the “Thanksgiving rain crust”.
The photo above shows a fresh glide avalanche on the south face of Tincan Proper. Notice the multiple runout paths. We are still in an active glide avalanche cycle that has been going on for the past 3 weeks. Be aware of your travel routes and try to avoid spending time below the gaping cracks.
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 SUN NOV 28 2010
…STRONG WIND THIS EVENING THROUGH TUESDAY AFTERNOON NEAR SEWARD AND
.TODAY…SNOW IN THE MORNING…THEN SCATTERED SNOW SHOWERS IN THE
AFTERNOON. SNOW ACCUMULATION UP TO 1 INCH. HIGHS IN THE LOWER 20S
TO LOWER 30S…COOLEST INLAND. NORTHWEST WIND 10 TO 15 MPH EXCEPT
NORTH 25 TO 35 MPH NEAR SEWARD.
.TONIGHT…PARTLY CLOUDY. LOWS 5 TO 20 ABOVE…COOLEST INLAND. WEST
WIND 35 TO 50 MPH NEAR WHITTIER. NORTH WIND 30 TO 45 MPH NEAR SEWARD.
NORTHWEST WIND 10 TO 20 MPH ELSEWHERE.
.MONDAY…PARTLY CLOUDY. HIGHS 10 TO 25 ABOVE. WEST WIND 35 TO 50 MPH
NEAR WHITTIER. NORTH WIND 30 TO 45 MPH NEAR SEWARD. NORTHWEST WIND 10
TO 20 MPH ELSEWHERE.
TEMPERATURE / PRECIPITATION
SEWARD 30 20 20 / 80 0 0
GIRDWOOD 25 13 15 / 70 0 0
WEATHER STATION SUMMARY for Turnagain Pass:
-3800′ Sunburst Wx Station-
recorded light west winds yesterday and temps ranging from 17-20F. The current temp is 18F with winds averaging 2-5mph out of the east.
-2600′ Seattle Ridge Wx Station-
recorded light north winds yesterday and temps ranging from 20-22F. The current temp is 17F with winds averaging 2-5mph out of the northeast.
-1800′ Center Ridge Wx Station-
recorded 3 inches of new snow and 0.2” water in the last 24 hours. Temps yesterday ranged from 20-25F. The current temp is 17F with a total snowpack depth of 47 inches.