Turnagain Pass

Good morning backcountry travelers this is Lisa Portune with the Chugach National Forest Avalanche Information Center on Monday, November 30 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

Turnagain Pass snowmachine area is open to motorized use. All CNFAIC Staff areas including Johnson Pass, Placer, Twenty-Mile, and all areas on the Seward Ranger District will remain closed until there is more snow. The Turnagain Pass open riding area is on the west side of the highway from Bertha Creek Campground north to the Forest boundary near the Turnagain Arm.

ATTENTION SNOWMACHINERS!!! Avalanche danger may exist at any time in backcountry areas like Turnagain Pass on the Chugach National Forest, whether these areas are open or closed. The US Forest Service does not close areas due to avalanche danger. When areas designated for use by snowmachines on the Chugach National Forest are closed, a primary reason is for the protection of natural resources in accordance with the current Forest Plan. Similarly, on open sign does not mean that it is safe. There are many inherent dangers associated with traveling in the backcountry including avalanches. Safe backcountry travel requires training and experience. You Control Your Own Risk by choosing where, when and how to travel. The Chugach National Forest Avalanche Information Center provides pertinent information to assist you in making your own decisions for traveling in these backcountry areas. Opening of these motorized areas in the early season can be subject to immediate closure based on sufficient snow to prevent the tracks of a snowmachine from tearing up vegetation. If the weather changes and the snowpack gets too thin to prevent resource damage, then areas may be closed again. It is your responsibility to check the official open/closed status of these areas with the Chugach National Forest. CNFAIC Staff resources for information regarding these motorized areas can be found through the Glacier Ranger District, and/or the Chugach National Forest Avalanche Information Center.

An educational opportunity is coming up to learn more about mountain weather on Dec 5th: “Weather for the Backcountry Traveler” Lecture Series. Given by AK Avalanche School and the NWS 9am-5pm; visit www.alaskaavalanche.com for more info.

WEATHER ROUNDUP

In the last 24 hours, 4-8 inches of new snow fell in Turnagain Pass and the Girdwood Valley. Ridgetop winds were light and variable yesterday, and mountain temperatures dropped to the low to mid teens. As of 1 am this morning, mountain winds have increased significantly and will continue to get stronger as the day progresses. The front associated with the strong low in the Bering Sea will bring gale to storm force winds to the Turnagain Arm area with possible hurricane force gusts. Ridgetop winds are currently averaging 20-25 mph out of the east and southeast with gusts in the 40’s and 50’s. Mountain temperatures range from 23 deg F at 1800′ to 15 deg F at 3800′. Weather models are predicting over 1 inch of snow water equivalent today in the form of 5-12 inches of new snow. Temperatures will warm up to the 30’s this afternoon, and the winds will increase to 40 to 65 mph out of the south and east. A Winter Storm Warning is in effect from 9am this morning to 3am Tuesday.

-The NRCS Center Ridge weather station at 1800 feet in Turnagain Pass-

recorded 5 inches of new snow (my best guess) and 0.2 inches of water. The current temp is 23F (1 degree warmer than yesterday)

-The Sunburst weather station at 3800 feet in Turnagain Pass-

recorded light northwest winds all day yesterday. The winds picked up around midnight and are currently averaging 20-25 out of the east with gusts in the 40’s. The current temp is 15F (4 degrees colder than yesterday).

The weather forecast for:

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

500 AM AKST MON NOV 30 2009

…WINTER STORM WARNING IN EFFECT FROM 9 AM THIS MORNING TO 3 AM

AKST TUESDAY…

.TODAY…SNOW INCREASING THIS MORNING THEN BECOMING MIXED WITH RAIN

BELOW 1500 FT THIS AFTERNOON. SNOW ACCUMULATIONS 5 TO 12 INCHES WITH

HEAVIER AMOUNTS AT HIGHER ELEVATIONS. PRECIPITATION MAY

BE HEAVY AT TIMES IN THE AFTERNOON. BLOWING SNOW WILL OCCASIONALLY

REDUCE VISIBILITIES BELOW ONE QUARTER MILE AT TIMES THROUGH EARLY

THIS AFTERNOON FROM PORTAGE VALLEY TO TURNAGAIN PASS. HIGHS IN THE

30S. THROUGH PORTAGE VALLEY AND TURNAGAIN ARM…EAST WINDS 30 TO 50

MPH INCREASING 40 TO 65 MPH WITH GUSTS TO 80 MPH THIS AFTERNOON.

ELSEWHERE…SOUTH TO EAST WINDS 30 TO 50 MPH.

.TONIGHT…RAIN AND SNOW…HEAVY AT TIMES IN THE EVENING. SNOW

ACCUMULATIONS 1 TO 3 INCHES…HEAVIER AMOUNTS AT HIGHER ELEVATIONS.

LOWS IN THE 30S. THROUGH PORTAGE VALLEY AND TURNAGAIN…EAST WINDS 30

TO 50 MPH INCREASING 40 TO 65 MPH WITH GUSTS TO 80 MPH THIS

AFTERNOON.

TEMPERATURE / PRECIPITATION

SEWARD 38 37 37 / 100 100 100

GIRDWOOD 33 33 35 / 70 90 70

AVALANCHE DISCUSSION

Gale to storm force winds and up to a foot of new snow will increase the avalanche hazard today. Dangerous avalanche conditions will develop as this storm progresses. For today, the avalanche danger is rated CONSIDERABLE on all slopes steeper than 35 degrees. Cautious routefinding and conservative decision-making are essential. Today is the day to dial it back by sticking to low angle terrain and staying out from under big open steep slopes. Strong winds will easily transport this past week’s storm snow to leeward aspects where human-triggered avalanches will be likely on slopes steeper than 35 degrees, and natural avalanches will be possible on actively loading westerly slopes. Visibly drifting snow, shooting cracks, and hollow drum-like hard snow are the most obvious clues to wind slab formation.

Besides today’s danger from wind-loading, further instability is associated with a layer of weak faceted snow at the bottom of our snowpack that continues to show signs of instability. This weak layer is buried 4-5 feet deep in most locations. Keep in mind that additional load from new and wind-blown snow will further stress this layer today. A ski party on Eddies yesterday noticed collapsing of the snowpack, most likely on the facet layer. Matt, Kris, Heather, and I dug multiple snowpits on Tincan yesterday, and although we didn’t see or hear any obvious signs of instability during our tour, our compression test scores at 2000 feet elevation indicated CNFAIC Staffwise. Check out the YouTube video I took of Matt doing a compression test by clicking on the button at the top of this page. The facets failed easily after three measly taps (CTE3Q3@160cm). This definitely got our attention. At 3000 feet elevation, the facets failed after 16 taps (CTM16Q3@126cm). What does all of this mean? It means we chose a conservative line back down because we do not trust this layer yet.

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 1st. Have a great day.