Good morning backcountry travelers this is Lisa Portune with the Chugach National Forest Avalanche Information Center on Monday, December 7 at 7 am. This will serve as a general backcountry avalanche advisory issued for Turnagain Arm with Turnagain Pass as the core advisory area (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. We are monitoring the snow at Placer and 20 Mile and will open those areas as soon as there is enough snow.
A strong blocking ridge continues to deflect storms and keep the weather dry and mild. Our last significant snowfall was six days ago on Tuesday December 1st. Yesterday ridgetop winds averaged 5-20 mph out of the east in Turnagain Pass and 5-20 mph out of the northwest in the Summit Lake area. Mountain temperatures climbed to the mid to upper 30’s yesterday.
As of 4 am this morning, ridgetop winds are light and variable at all locations. Temperatures, however, are anCNFAIC Staff story. Unusually warm air aloft has caused a dramatic temperature inversion with temps in the teens at sea level but well into the low 40’s at the higher elevations. Many locations above 3000 feet have been at 40F or higher since midnight. Portage is currently 13F, Girdwood 18F, top of Max’s 40F, and Sunburst 41F. These crazy temps look like they will stick around at least through Tuesday. High level clouds should erode today as surface high pressure builds over the gulf, and the winds should remain light. This monster omega block looks like it will hold through the end of the week bringing continued clear and dry weather.
-The Center Ridge Wx Station at 1800 feet/Turnagain Pass-
recorded no new snow. The current temp is 34F (same as yesterday) with a total snowpack depth of 62 inches (2 inches of settlement since yesterday)
-The Sunburst Wx Station at 3800 feet/Turnagain Pass-
recorded light easterly winds yesterday averaging 5-15 mph with s few gusts in the 20’s. The current temp is 41F (11 degrees warmer than yesterday) with light and variable winds.
-The Summit Lake Wx Station at 1200 feet-
recorded no new snow. The current temp is 15F (12 degrees colder than yesterday) with a total snowpack depth of 27 inches (same as yesterday).
-The Fresno Ridge Wx Station at 3400 feet/Summit Lake-
recorded light to moderate northwest winds yesterday averaging 5-20 mph with gusts in the 20’s. The current temp is 39F (9 degrees warmer than yesterday) with light and variable winds.
The weather forecast for:
WESTERN PRINCE WILLIAM SOUND-
500 AM AKST MON DEC 7 2009
.TODAY…PARTLY CLOUDY IN THE MORNING THEN BECOMING SUNNY. HIGHS
IN THE UPPER 20S TO MID 30S. LIGHT WINDS EXCEPT WEST 10 TO 15 MPH
.TONIGHT…CLEAR. LOWS IN THE MID TEENS TO LOWER 30S…COLDEST
INLAND. VARIABLE WIND 10 MPH.
.TUESDAY…SUNNY. HIGHS IN THE UPPER 20S TO UPPER 30S. LIGHT
WINDS EXCEPT WEST 15 TO 20 MPH NEAR WHITTIER.
.TUESDAY NIGHT…MOSTLY CLEAR. LOWS IN THE MID TEENS TO LOWER
30S…COLDEST INLAND. LIGHT WINDS EXCEPT WEST 15 TO 20 MPH NEAR
.WEDNESDAY…MOSTLY SUNNY. HIGHS IN THE 30S. LIGHT WINDS.
.WEDNESDAY NIGHT…CLEAR. LOWS IN THE 20S.
.THURSDAY THROUGH FRIDAY…MOSTLY CLEAR. HIGHS IN THE 30S. LOWS
IN THE 20S.
TEMPERATURE / PRECIPITATION
SEWARD 34 28 37 / 0 0 0
GIRDWOOD 31 18 32 / 0 0 0
The avalanche danger remains at MODERATE today due to unseasonably warm temperatures in the 40’s at the higher elevations. A moderate danger level means that natural avalanches are unlikely but human-triggered avalanches are possible on slopes steeper than 35 degrees. Our main area of concern lies at the ground where we still see 4-10 inches of weak faceted crystals that formed during the cold snap in mid November. Numerous medium to large natural avalanches failed on this layer last Tuesday during the latest storm. Although it seems to have lost most of its reactivity, 40 degree temps at the higher elevations may stress this layer. The big unknown is how the snowpack will react, so keep a heads up. Evaluate the snow and terrain carefully and always use good travel habits.
Skiers and riders were inching back into steeper terrain this past weekend with generally stable conditions. We did not see or hear of any human-triggered avalanches, and the snowpack gave up no obvious signs of instability. Snow conditions vary from 4-8 inches of powder down low in the trees and alders to windbuffed powder, supportable windslab, and punchy breakable crust up high.
Matt and I toured up Sunburst yesterday to 3500 feet elevation and confirmed what many folks have been seeing in their snowpits…the November facet layer at the base of the snowpack is strengthening and has lost its reactivity. Our isolated column stability tests produced no failure on this layer or a low energy failure on the 30th tap. We also found that the windslabs that formed on Saturday quickly bonded to the old snow surface and were not reactive to ski cuts. Also, numerous glide cracks were reported in the north facing trees on Tincan. Be careful not to fall into one of these crevasse-like openings.
If you have observations for us please send them using the observations button at the top of the advisory page of our website. This concludes today’s advisory. The next advisory will be Tuesday, December 8th. Thanks and have a great day.