Turnagain Pass

Good morning backcountry travelers this is Lisa Portune with the Chugach National Forest Avalanche Information Center on Sunday, December 27 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

Placer River Drainage and Twentymile are closed to snowmachining due to heavy rain and warm temps at sea level.

WEATHER ROUNDUP

Yesterday 2-4 inches of new snow fell at the higher elevations of Turnagain Pass while the rain/snow line hovered around 1500-2000feet. Ridgetop winds averaged 10-20mph out of the east and southeast while mountain temperatures ranged from the mid 20’s to mid 30’s.

As of 4 am this morning, ridgetop winds have increased and are currently averaging 25-30mph out of the east to southeast with gusts in the 40’s and 50’s in Turnagain Pass. It is raining steadily in Girdwood right now with temperatures ranging from 42F at sea level to 27F at 3800 feet. The rain/snow line looks to be around 2000-2300 feet this morning.

Warm southeasterly flow will continue today bringing more rain to the lower elevations. Today should hopefully be the last day of our weeklong meltdown as high pressure begins to build in from the east on Monday. Expect strong east to southeast winds averaging 25-35mph this morning gradually decreasing by late this afternoon. Mountain temperatures will remain on the warm side, ranging from the mid 20’s to mid 30’s.

-The Center Ridge Wx Station at 1800 feet/Turnagain Pass-

recorded 2-4 inches of new snow and 0.2 inches of water in the last 24 hours. The current temp is 33F (2 degrees warmer than yesterday) with a total snowpack depth of 65 inches.

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

recorded light to moderate east winds yesterday averaging 10-20mph with gusts in the 20’s. The current temp is 27F (2 degrees warmer than yesterday) with winds averaging 30 mph out of the east.

-The Summit Lake Wx Station at 1200 feet-

recorded 0 inches of new snow in the last 24 hours. The current temp is 35F (3 degrees warmer than yesterday) with a total snowpack depth of 31 inches.

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

recorded moderate southeasterly winds yesterday averaging 15-20mph with gusts in the 20’s. The current temp is 27F (1 degree warmer than yesterday) with winds averaging 20mph out of the southeast.

The weather forecast for:

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKST SUN DEC 27 2009

…STRONG WIND THROUGH SUNDAY AFTERNOON FOR PORTAGE VALLEY AND ALONG

TURNAGAIN ARM…

.TODAY…RAIN AND SNOW SHOWERS. NO SNOW ACCUMULATIONS. HIGHS AROUND

40. NORTH TO EAST WIND TO 15 MPH EXCEPT EAST 30 TO 45 MPH THROUGH

PORTAGE VALLEY AND TURNAGAIN ARM.

.TONIGHT…SCATTERED RAIN AND SNOW SHOWERS. NO SNOW ACCUMULATION.

LOWS IN THE UPPER 20S TO MID 30S. NORTH TO EAST WIND TO 15 MPH EXCEPT

EAST 20 TO 35 MPH THROUGH PORTAGE VALLEY AND TURNAGAIN ARM.

.MONDAY…MOSTLY CLOUDY. ISOLATED RAIN AND SNOW SHOWERS

IN THE MORNING…THEN ISOLATED RAIN SHOWERS IN THE AFTERNOON.

HIGHS IN THE 30S. NORTH AND EAST WIND TO 10 MPH EXCEPT

EAST 10 TO 20 MPH THROUGH PORTAGE VALLEY AND TURNAGAIN ARM.

TEMPERATURE / PRECIPITATION

SEWARD 42 29 37 / 60 40 20

GIRDWOOD 39 21 34 / 60 40 0

AVALANCHE DISCUSSION

The avalanche danger remains MODERATE today on slopes steeper than 35 degrees. Human-triggered avalanches are possible on the new storm snow/windslab above 2000 feet and on the buried surface hoar below 2000 feet. Natural avalanches are unlikely today.

We have two distinct snowpacks going on right now: the one above 2000 feet and the one below 2000 feet. Below 2000 feet, conditions range from wet glop to breakable rain crust. The surface hoar that formed the second week of December is now buried 1-2 feet deep at these lower elevations. It was reactive as recently as 3 days ago when numerous natural and human-triggered avalanches occurred on this layer. Most were small in size, up to 50 feet wide, and confined to steep rollovers below treeline. Jon and I toured up Sunburst yesterday and found the surface hoar buried 1 ft. deep. Although it fractured cleanly in our stability tests, it lacked the energy to propagate a fracture. (Check out our video of an extended column test on this layer by clicking on the button at the top of this page). Despite this lack of reactivity, I would still approach these lower elevation steep slopes with caution, especially on the northern end of Turnagain Pass where the surface hoar is buried deeper and thus more protected from the warm temps and rain.

Above 2000 feet, the conditions are dramatically different. The snow is actually quite good. Surface instabilities from the new storm snow and windslab still exist in the top foot or so, but these should stabilize quickly whenever the temps cool off. I would approach steep unsupported convexities with caution and stay off of the big open slopes in the meantime.

Jon and I found a nice shallow spot to dig yesterday at 2400 feet and unfortunately found that the November facets at the ground (remember those?) are becoming less stable. In the last 3 weeks our compression test scores have been gradually decreasing on this layer, from CT30 to 24 to 20 to 13. We shot anCNFAIC Staff little video yesterday of our test results. Although the facets look to be rounding out and strengthening, our snowpit results say CNFAIC Staffwise.

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.