Turnagain Pass Avalanche Forecast

Good morning backcountry travelers this is Matt Murphy with the Chugach National Forest Avalanche Information Center on Tuesday December 1st 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

More areas designated for snowmachines (except Placer and 20 Mile) on the Chugach National Forest will open today Dec 1 at 1200 noon. We are monitoring the snow at Placer and 20 Mile and will open those areas as soon as there is enough snow.

ATTENTION!!!

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 inherrant 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 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,Seward Ranger District and/or the Chugach National Forest Avalanche Information Center.

Thanks for being safe!

WEATHER ROUNDUP

Will recent weather affect avalanche conditions today?

Well, let’s take a closer look at the precip, winds, and temps.

Hindcast (Last 24 hours)

3800′ -Sunburst Wx Station-

Temp: 26 (11 degrees warmer than yesterday)

Wind: averaged 19-66 mph out of the East with a max gust of 92 mph

2600′-Seattle Ridge Wx Station-

Wind: averaged 16-39 mph out of the SE with a max gust of 73 mph

1800′-Center Ridge Wx Station-

Precip: 2.9 inches of water

34” of new snow for a total snowpack depth of 89”

Temp: 32 degrees (9 degrees warmer than yesterday)

Nowcast (OTW)

Temps are warmer at all weather stations from Girdwood to Summit Lake by 6-11 degrees. The temps range from 36 degrees at sea level to 31 degrees at 2800 feet; so, the freeze line is probably between 2000-2500 feet.

Rain is currently falling moderately in Girdwood, and the radar is full of moderate precip. Moderate to strong winds are still being recorded on ridgetops averaging as high as 31 mph on Sunburst

Forecast

WESTERN PRINCE WILLIAM SOUND-

INCLUDING…WHITTIER…SEWARD…GIRDWOOD…MOOSE PASS

520 AM AKST TUE DEC 1 2009

…STRONG WIND THROUGH THIS EVENING THROUGH PORTAGE VALLEY AND

TURNAGAIN ARM…

.TODAY…RAIN AND SNOW. SNOW ACCUMULATION 4 TO 8 INCHES IN THE HIGHER

ELEVATIONS. HIGHS IN THE LOWER 30S TO LOWER 40S. SOUTH AND EAST WIND

25 TO 35 MPH. THROUGH PORTAGE VALLEY AND TURNAGAIN ARM…SOUTHEAST

WIND 35 TO 50 MPH.

.TONIGHT…RAIN AND SNOW IN THE EVENING BECOMING SCATTERED RAIN AND

SNOW SHOWERS AFTER MIDNIGHT. SNOW ACCUMULATION 3 TO 6 INCHES. LOWS IN

THE MID 20S TO MID 30S. SOUTH AND EAST WIND TO 15 MPH. THROUGH

PORTAGE VALLEY AND TURNAGAIN ARM…EAST WIND 30 TO 45 MPH BECOMING

SOUTHEAST 15 TO 20 MPH AFTER MIDNIGHT.

.WEDNESDAY…MOSTLY CLOUDY WITH SCATTERED SNOW AND RAIN SHOWERS.

HIGHS IN THE MID 20S TO UPPER 30S. SOUTHEAST WIND 10 TO 20 MPH.

TEMPERATURE / PRECIPITATION

SEWARD 40 34 35 / 100 100 100

GIRDWOOD 40 29 36 / 100 100 80

The weather models are predicting about 2” of more water today for the area around the Kenai Mountains with the freeze line reaching as high as 3000′. Plus the NWS is still calling for strong wind today.

AVALANCHE DISCUSSION

The weather is contributing to the avalanche danger today, and the level of uncertainty with the snowpack is very high today. With that being said, I rate today’s avalanche hazard as CONSIDERABLE TO HIGH based on past and current weather and recent snowpit data. Very dangerous avalanche conditions exist today. There is potential for very large and deep slab avlanches today.

We’ve been trying to get a baseline of the snowpack with pits at different elevations on Tincan over the past week. The weather has been so intense since last Monday (Nov 23) and has been changing so frequently that it is difficult for me to say anything about the snowpack with too much confidence. I want to say that all this snow will create one of the best bases we have seen in years, and that it will be stable after the weather mellows out, but we can’t ignore the data we have seen in our snowpits.

In simple terms, we have a dense slab on top of a weak layer of facets. All the new storm snow seems to be bonding to itself (creating a slab) very well. This dense snow seems to be supporting the weight of skiers/snowboarders and snowmachiners and this part of the snowpack is strong. When we have isolated columns, however, we have found poor stability with easy failures all the way to the facets on the ground. I still have not been on a slope steeper than 35 degrees this year because I don’t completely trust our snowpack.