Turnagain Pass

Good morning backcountry travelers this is Lisa Portune with the Chugach National Forest Avalanche Information Center on Sunday, December 6 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).

ANNOUNCEMENTS

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.

WEATHER ROUNDUP

A strong blocking ridge has put the kibosh on new snow for now, but the winds have been a different story. Ridgetop winds picked up around 11am yesterday, averaging 20-35 mph out of the east in Turnagain Pass and 20-30 mph out of the NW in the Summit Lake area. Mountain temperatures climbed to the upper 20’s to low 30’s yesterday. Our last significant snowfall was five days ago on Tuesday December 1st. As of 4 am this morning, mountain winds have decreased a bit in Turnagain Pass averaging 10-20 mph out of the east and southeast. Ridgetop winds continue to average 20 mph out of the NW in the Summit lake area. Mountain temperatures are unseasonably warm and currently range from 27-36F with Portage coming in at a balmy 40F. Temps will remain above freezing at the higher elevations today, and the winds should diminish by afternoon. This omega block of high pressure 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 35F (9 degrees warmer than yesterday) with a total snowpack depth of 64 inches (3 inches of settlement since yesterday)

-The Sunburst Wx Station at 3800 feet/Turnagain Pass-

recorded moderate to strong east winds yesterday and last night averaging 20-35 mph with gusts in the 40’s and 50’s. The current temp is 30F (6 degrees warmer than yesterday) with 10 mph winds out of the east.

-The Summit Lake Wx Station at 1200 feet-

recorded no new snow. The current temp is 27F (8 degrees warmer than yesterday) with a total snowpack depth of 27 inches (1 inch of settlement since yesterday).

-The Fresno Ridge Wx Station at 3400 feet/Summit Lake-

recorded moderate to strong northwest winds yesterday and last night averaging 15-30 mph with gusts in the 20’s and 30’s. The current temp is 31F (2 degrees warmer than yesterday) with 20 mph winds out of the northwest.

The weather forecast for:

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKST SUN DEC 6 2009

.TODAY…MOSTLY CLOUDY IN THE MORNING THEN BECOMING PARTLY CLOUDY.

HIGHS IN THE LOWER 30S TO LOWER 40S. EAST WIND 5 TO 15 MPH. THROUGH

PORTAGE VALLEY AND TURNAGAIN ARM…SOUTHEAST WIND 20 TO 30

MPH…DIMINISHING IN THE AFTERNOON.

.TONIGHT…MOSTLY CLEAR. LOWS 15 TO 25…COLDEST INLAND. VARIABLE

WIND TO 10 MPH.

.MONDAY…MOSTLY SUNNY. HIGHS IN THE UPPER 20S TO MID 30S. LIGHT

WINDS. NEAR WHITTIER…LIGHT WINDS BECOMING WEST 15 MPH IN THE

AFTERNOON.

.MONDAY NIGHT…MOSTLY CLEAR. LOWS 15 TO 25. LIGHT WINDS. NEAR

WHITTIER…WEST WIND 15 MPH IN THE EVENING BECOMING LIGHT.

.TUESDAY…MOSTLY SUNNY. HIGHS IN THE UPPER 20S TO MID 30S. LIGHT

WINDS.

.TUESDAY NIGHT…MOSTLY CLEAR. LOWS 15 TO 25.

.WEDNESDAY THROUGH FRIDAY…MOSTLY CLEAR. HIGHS IN THE 30S. LOWS

15 TO 25.

TEMPERATURE / PRECIPITATION

SEWARD 38 22 32 / 0 0 0

GIRDWOOD 38 19 30 / 0 0 0

AVALANCHE DISCUSSION

The avalanche danger remains at MODERATE today which means that natural avalanches are unlikely but human-triggered avalanches are possible on slopes steeper than 35 degrees. Pockets of sensitive windslab may remain from yesterday’s and last night’s winds, but I would expect any avalanches on these surface layers to be small and not propagate very far. Additional windslab may develop this morning on leeward aspects with continued moderate to strong winds. Watch for crossloading midway down slopes that may catch you off guard.

Our main area of concern, however, lies at the ground where we still see weak faceted crystals from early November. Numerous medium to large natural avalanches failed on this layer this past Tuesday during the latest storm. (Check out our photo gallery for examples). Although it seems to have lost most of its reactivity, additional load from windblown snow may further stress this layer. Unusually warm temps above freezing today may also stress this layer by causing the surface slab to settle and creep more rapidly. In CNFAIC Staff words, I don’t think we can write off the facets just yet. There is always the possibility of triggering an avalanche on this layer, especially in areas where the snowpack is shallow.

Lots of folks were out and about yesterday in Turnagain Pass with groups on every ridge from Eddies to Lipps. Most of the groups I spoke with reported good skiing and riding conditions, especially down low off of the ridgetops, and no obvious signs of instability on the basal facet layer. Several groups reported no failures on the facet layer during their isolated column stability tests. One of our observers reported finding newly formed windslab midway down Cornbiscuit on a crossloaded terrain feature that was reactive to ski cutting. The depth of the slab varied from a few inches to 6-8 inches. The winds also seemed to be stronger on the south end of the pass with plumes and snow whirls visible on the ridgetops.

AnCNFAIC Staff one of our observers down at Summit Lake reported similar conditions on Tenderfoot Ridge (the old ski hill) with no signs of instability on the facet layer near the ground. AnCNFAIC Staff group skied a higher elevation north aspect of the old ski hill and reported good stability. High winds were also observed loading west aspects around Carter Lake and Lost Lake. 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 Monday, December 7th. Thanks and have a great day.